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Nathan Smith

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The Nutrition Source - Harvard Chan School

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Salt, also known as sodium chloride, is about 40% sodium and 60% chloride. It flavors food and is used as a binder and stabilizer. It is also a food

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Nutritional Strategies for Enhancing Performance and Training 

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Nutritional Strategies for Enhancing Performance and Training 

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How to strategically and nutritionally enhance your training.

Brady Barnett

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Nutritional Strategies for Enhancing Performance and Training Adaptation in Weightlifters

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Weightlifting demands explosive power and neuromuscular coordination in brief, repeated intervals. These physiological demands underscore the critical role of nutrition, not only in optimizing performance during competitions but also in supporting…

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BMC research and recommendations on sports nutrition

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BMC research and recommendations on sports nutrition

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Phillip Maxie

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ISSN exercise & sports nutrition review update: research & recommendations - Journal of the International Society of Sports Nutrition

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Background Sports nutrition is a constantly evolving field with hundreds of research papers published annually. In the year 2017 alone, 2082 articles were published under the key words ‘sport nutrition’. Consequently, staying current with the relevant literature is often difficult. Methods This paper is an ongoing update of the sports nutrition review article originally published as the lead paper to launch the Journal of the International Society of Sports Nutrition in 2004 and updated in 2010. It presents a well-referenced overview of the current state of the science related to optimization of training and performance enhancement through exercise training and nutrition. Notably, due to the accelerated pace and size at which the literature base in this research area grows, the topics discussed will focus on muscle hypertrophy and performance enhancement. As such, this paper provides an overview of: 1.) How ergogenic aids and dietary supplements are defined in terms of governmental regulation and oversight; 2.) How dietary supplements are legally regulated in the United States; 3.) How to evaluate the scientific merit of nutritional supplements; 4.) General nutritional strategies to optimize performance and enhance recovery; and, 5.) An overview of our current understanding of nutritional approaches to augment skeletal muscle hypertrophy and the potential ergogenic value of various dietary and supplemental approaches. Conclusions This updated review is to provide ISSN members and individuals interested in sports nutrition with information that can be implemented in educational, research or practical settings and serve as a foundational basis for determining the efficacy and safety of many common sport nutrition products and their ingredients.

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Creatine and Beta-Alanine Supplementation for Increased Anaerobic Performance in Sprinting, Jumping, and Throwing Track and Field Athletes

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Creatine and Beta-Alanine Supplementation for Increased Anaerobic Performance in Sprinting, Jumping, and Throwing Track and Field Athletes

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Brayden Arnett

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1. Judge, L.W., J.C. Petersen, B.W. Craig, D.L. Hoover, K.A. Holtzclaw, B.N. Leitzelar, and D.M. Bellar, Creatine usage and education of track and field throwers at National Collegiate Athletic Association Division I universities. Journal of Strength and Conditioning Research, 2015. 29(7), 2034- 2040.

2. Heikkinen, A., A. Alaranta, I. Helenius, and T. Vasankari, T, Dietary supplementation habits and perceptions of supplement use among elite Finnish athletes. International Journal of Sport Nutrition and Exercise Metabolism, 2011. 21(4), 271-279.

3. Zuniga, J. M., T.J. Housh, C.L. Camic, C.R. Hendrix, M. Mielke, G.O. Johnson, and R.J. Schmidt, The effects of creatine monohydrate loading on anaerobic performance and one-repetition maximum strength. Journal of Strength and Conditioning Research, 2012. 26(6), 1651-1656.

4. Smith, A.E., D.H. Fukuda, K.L. Kendall, and J.R. Stout, The effects of a pre- workout supplement containing caffeine, creatine, and amino acids during three weeks of high-intensity exercise on aerobic and anaerobic performance. Journal of the International Society of Sports Nutrition, 2010. 7(1), 10. doi:10.1186/1550-2783-7-10

5. Tscholl, P., J.M. Alonso, G. Dollé, A. Junge, and J. Dvorak, The use of drugs and nutritional supplements in top-level track and field athletes. The American Journal of Sports Medicine, 2010. 38(1), 133-140.

6. Kirksey, B., M.H. Stone, B.J. Warren, R.L. Johnson, M. Stone, G.G. Haff, and C. Proulx, The Effects of 6 Weeks of Creatine Monohydrate Supplementation on Performance Measures and Body Composition in Collegiate Track and Field Athletes. Journal of Strength and Conditioning Research, 1999. 13(2), 148-156.

7. Lamontagne-Lacasse, M., R. Nadon, and E. Goulet, Effect of creatine supplementation on jumping performance in elite volleyball players.
International Journal of Sports and Physiological Performance, 2011. 6(4):525- 33.

8. Ciccone, V., K. Cabrera, and J. Antonio, J, (2013). The effects of pre- versus post-workout supplementation of creatine monohydrate on body composition and strength. Journal of the International Society of Sports Nutrition, 10(Suppl 1). doi:10.1186/1550-2783-10-s1-p1

9. Sale, C., B. Saunders, and R.C. Harris, Effect of beta-alanine supplementation on muscle carnosine concentrations and exercise performance. Amino Acids, 2009. 39(2), 321-333.

10. Saunders, B., C. Sale, R.C. and C. Sunderland, Effect of beta-alanine supplementation on repeated sprint performance during the Loughborough Intermittent Shuttle Test. Amino Acids, 2012. 43(1), 39-47.

11. Jagim, A. R., G.A. Wright, A.G Brice, and S.T. Doberstein, Effects of beta- alanine supplementation on sprint endurance. Journal of Strength and Conditioning Research, 2013. 27(2), 526-532.

12. Ducker, K. J., B. Dawson, and K.E. Wallman, Effect of beta-alanine supplementation on 800-m running performance. International Journal of Sport Nutrition and Exercise Metabolism, 2013. 23(6), 554-561.

13. Derave, W., M.S. Ozdemir, R.C. Harris, A. Pottier, H. Reyngoudt, K. Koppo, J.A.Wise, and E. Achten E, beta-Alanine supplementation augments muscle carnosine content and attenuates fatigue during repeated isokinetic contraction bouts in trained sprinters. Journal of Applied Physiology,
2007. 103(5):1736-43.

14. Deminice, R., F.T. Rosa, G.S. Franco, A.A, Jordao, and E.C. Freitas, Effects of creatine supplementation on oxidative stress and inflammatory markers after repeated-sprint exercise in humans. Nutrition, 2013. 29(9), 1127-1132.

15. Jordan, T., J. Lukaszuk, M. Misic, M., and J. Umoren, Effect of beta-alanine supplementation on the onset of blood lactate accumulation (OBLA) during treadmill running: Pre/post 2 treatment experimental design. Journal of the International Society of Sports Nutrition, 2010. 7(1), 20.
doi:10.1186/1550- 2783-7-20

16. Harris, RC., R.H. Edwards, E. Hultman, L.O. Nordesjö, B. Nylind, and K. Sahlin, The time course of phosphorylcreatine resynthesis during recovery of the quadriceps muscle in man. Pflugers Archives, 1976 367(2):137-42.

17. Rampinini, E., A. Sassi, A. Morelli, S. Mazzoni, M. Fanchini, and A.J, Repeated-sprint ability in professional and amateur soccer players. Applied Physiology Nutrition and Metabolism, 2009 34(6):1048-54.

18. Donaldson, S.K.B., and L. Hermansen, Differential direct effects of H+ and Ca2+-activated force of skinned fibres from the doleus, cardiac, adductor magnus muscle of rabbits. European Journal of Physiology, 1978. 376:55-65.

19. Fabiato, A., and F. Fabiato, Effects of pH on the
myofilaments and the sarcoplasmic reticulum of skinned cells from cardiac and skeletal muscles. Journal of Physiology, 1978. 276:233-35.

20. Trivedi, B., and W.H. Daniforth, Effect of pH on the kinetics of frog muscle phosphocreatine. Journal of Biological Chemistry, 1984. 241:4110-12.

21. Spriet, L.L., M.I. Lindinger, R.S. McKelvie, G.J.F. Heigenhauser, and N.L. Jones, Muscle glycogenolysis and H+ concentration during maximal intermittent cycling. Journal of Applied Physiology, 1989. 66:8-13.

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Abstract Track and field athletes involved in sprinting, jumping, and throwing events are one of the largest groups utilizing both speed and power. As a result, this group of athletes could potentially benefit from creatine and beta-alanine supplementation.

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Bella Hernandez

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Abstract

Following critical evaluation of the available literature to date, The International Society of Sports Nutrition (ISSN) position regarding caffeine intake is as follows:

1. Supplementation with caffeine has been shown to acutely enhance various aspects of exercise performance in many but not all studies. Small to moderate benefits of caffeine use include, but are not limited to: muscular endurance, movement velocity and muscular strength, sprinting, jumping, and throwing performance, as well as a wide range of aerobic and anaerobic sport-specific actions.

2. Aerobic endurance appears to be the form of exercise with the most consistent moderate-to-large benefits from caffeine use, although the magnitude of its effects differs between individuals.

3. Caffeine has consistently been shown to improve exercise performance when consumed in doses of 3-6 mg/kg body mass. Minimal effective doses of caffeine currently remain unclear but they may be as low as 2 mg/kg body mass. Very high doses of caffeine (e.g. 9 mg/kg) are associated with a high incidence of side-effects and do not seem to be required to elicit an ergogenic effect.

4. The most commonly used timing of caffeine supplementation is 60 min pre-exercise. Optimal timing of caffeine ingestion likely depends on the source of caffeine. For example, as compared to caffeine capsules, caffeine chewing gums may require a shorter waiting time from consumption to the start of the exercise session.

5. Caffeine appears to improve physical performance in both trained and untrained individuals.

6. Inter-individual differences in sport and exercise performance as well as adverse effects on sleep or feelings of anxiety following caffeine ingestion may be attributed to genetic variation associated with caffeine metabolism, and physical and psychological response. Other factors such as habitual caffeine intake also may play a role in between-individual response variation.

7. Caffeine has been shown to be ergogenic for cognitive function, including attention and vigilance, in most individuals.

8. Caffeine may improve cognitive and physical performance in some individuals under conditions of sleep deprivation.

9. The use of caffeine in conjunction with endurance exercise in the heat and at altitude is well supported when dosages range from 3 to 6 mg/kg and 4-6 mg/kg, respectively.

10. Alternative sources of caffeine such as caffeinated chewing gum, mouth rinses, energy gels and chews have been shown to improve performance, primarily in aerobic exercise.

11. Energy drinks and pre-workout supplements containing caffeine have been demonstrated to enhance both anaerobic and aerobic performance.

Introduction

Caffeine is the world's most widely consumed psychoactive substance and naturally occurs in dozens of plant species, including coffee, tea and cocoa. Caffeine is ingested most frequently in the form of a beverage such as coffee, soft drinks and tea, although the consumption of many functional beverages, such as energy drinks, has been on a steady rise in the past two decades [ 1]. In Western countries, approximately 90% of adults consume caffeine on a regular basis, with dietary caffeine consumption of U.S. adult men and women estimated at approximately 200 mg/day in a 2009-2010 survey [ 2- 4]. In young adults and exercising individuals, there has also been a rise in the consumption of other caffeine-containing products, including energy drinks [ 1, 3], 'pre-workout supplements', chewing gum, energy gels and chews, aerosols, and many other novel caffeinated food products [ 5]. Caffeine-containing products have a range of doses per serving, from 1 mg in milk chocolate up to > 300 mg in some dietary supplements [ 6].

Caffeine and its effects on health have been a longstanding topic of interest, and caffeine continues to be a dietary compound of concern in public health, as indicated by extensive investigations [ 7- 10]. At the same time, caffeine has become ubiquitous in the sporting world, where there is keen interest in better understanding the impact of caffeine on various types of exercise performance. Accordingly, caffeine has dominated the ergogenic aids and sport supplement research domain over the past several decades [ 11- 13].

Caffeine in sport: a brief history

In the early days (1900s) of modern sport, concoctions of plant-based stimulants, including caffeine and other compounds such as cocaine, strychnine, ether, heroin and nitroglycerin, were developed secretly by trainers, athletes and coaches, in what appears to be evidence for early day ergogenic aids designed to provide a competitive advantage [ 14]. The use of various pharmaceutical cocktails by endurance athletes continued until heroin and cocaine became restricted to prescriptions in the 1920s, and further when the International Olympic Committee (IOC) introduced anti-doping programs in the late 1960s [ 15].

Some of the earliest published studies on caffeine came from two psychologists and colleagues William Rivers and Harald Webber, at Cambridge University, who both had an interest in disentangling the psychological and physiological effects of substances like caffeine and alcohol. Rivers and Webber, using themselves as subjects, investigated the effects of caffeine on muscle fatigue. The remarkable well-designed studies carried out from 1906 to 1907 used double-blinded placebo-controlled trials and standardization for diet (i.e. caffeine, alcohol), and were described in a 1907 paper in the Journal of Physiology [ 16]. Significant research on the effects of caffeine on exercise performance with more subjects, different sports, and exploring variables such as the effects between trained and untrained individuals, began and continued through the 1940s [ 14, 17]. However, it was the series of studies investigating the benefits of caffeine in endurance sports in the Human Performance Laboratory at Ball State University in the late 1970s, led by David Costill [ 18, 19] and others [ 20], that sparked a generation of research on the effects of caffeine in exercise metabolism and sports performance.

Caffeine sources

Along with naturally occurring sources, such as coffee, tea and cocoa, caffeine is also added to many foods, beverages and novelty products, such as jerky, peanut butter, and candy, in both synthetic (e.g. powder) and natural (e.g. guarana, kola nut) forms. Synthetic caffeine is also an ingredient in several over-the-counter and prescription medications, as it is often used in combination with analgesic and diuretic drugs to amplify their pharmacological potency [ 21].

Approximately 96% of caffeine consumption from beverages comes from coffee, soft drinks and tea [ 22]. Additionally, there are varying levels of caffeine in the beans, leaves and fruit of more than 60 plants, resulting in great interest in herbal and other plant-based supplements [ 23- 26]. Caffeine-containing energy drink consumption [ 27- 31] and co-ingestion of caffeine with (e.g. "pre-workouts"), or in addition to, other supplements (e.g. caffeine + creatine) is also popular among exercising individuals [ 32- 39]. To date, the preponderance of caffeine and exercise performance literature has utilized anhydrous caffeine (in a capsule) [ 40- 46] for simpler dose standardization and placebo creation. There is also a growing body of literature studying the effects of using alternate delivery methods of caffeine during exercise [ 5] such as coffee [ 18, 47- 56], energy drinks, herbal formulas [ 57] and 'pre-workout' formulas, among others. A review of alternate caffeine forms may be found in the Alternative caffeine sources section and Tables 4, 5, 6, 7 and 8.

Caffeine legality in sport

Anti-doping rules apply to most sports, especially in those where athletes are competing at national and international levels. The IOC continues to recognize that caffeine is frequently used by athletes because of its reported performance-enhancing or ergogenic effects [ 109]. Caffeine was added to the list of banned substances by the IOC in 1984 and the World Anti-Doping Agency (WADA) in 2000. A doping offense was defined as having urinary caffeine concentrations exceeding a cut-off of 15 μg/ml. In 1985, the threshold was reduced to 12 μg/ml [ 110]. The cut-off value was chosen to exclude typical amounts ingested as part of common dietary or social coffee drinking patterns, and to differentiate it from what was considered to be an aberrant use of caffeine for the purpose of sports performance enhancement [ 111].

The IOC and WADA removed the classification of caffeine as a "controlled" substance in 2004, leading to a renewed interest in the use of caffeine by athletes. However, caffeine is still monitored by WADA, and athletes are encouraged to maintain a urine caffeine concentration below the limit of 12 μg/ml urine which corresponds to 10 mg/kg body mass orally ingested over several hours, and which is more than triple the intake reported to enhance performance [ 112, 113]. Interestingly, caffeine is also categorized as a banned substance by the National Collegiate Athletic Association (NCAA), if urinary caffeine concentration exceeds 15 μg/ml, which is greater than the "monitored substance" level set for WADA [ 114], and also well above amounts that are deemed ergogenic.

A comparison of caffeine concentrations obtained during in-competition doping control from athletes in several sports federations pre− 2004 versus post-2004, indicated that average caffeine concentrations decreased in 2004 after removal from the prohibited substance list [ 110]. Reports on over 20,000 urine samples collected and analyzed after official national and international competitions between 2004 and 2008, and again in 2015 using 7500 urine samples found overall prevalence of caffeine use across various sports to be about 74% in the 2004 to 2008 time period and roughly 76% in 2015. The highest use of caffeine was among endurance athletes in both studies [ 115, 116]. Urinary caffeine concentration significantly increased from 2004 to 2015 in athletics, aquatics, rowing, boxing, judo, football, and weightlifting; however, the sports with the highest urine caffeine concentration in 2015 were cycling, athletics, and rowing [ 116].

Caffeine pharmacokinetics

Caffeine or 1,3,7-trimethylxanthine, is an odorless white powder that is soluble in both water and lipids and has a bitter taste. It is rapidly absorbed from the gastrointestinal tract, mainly from the small intestine but also in the stomach [ 117]. In saliva, caffeine concentration reaches 65-85% of plasma levels, and is often used to non-invasively monitor compliance for ingestion or abstinence of caffeine [ 118]. Caffeine is effectively distributed throughout the body by virtue of being sufficiently hydrophobic to allow easy passage through most, if not all biological membranes, including the blood-brain barrier [ 119]. When caffeine is consumed it appears in the blood within minutes, with peak caffeine plasma concentrations after oral administration reported to occur at times (T max) ranging from 30 to 120 min [ 43, 120- 122]. The absolute bioavailability of caffeine is very high and reaches near 100% as seen in studies reporting areas under the plasma concentration-time curves (AUC) [ 120]. Once caffeine is absorbed, there appears to be no hepatic first-pass effect (i.e., the liver does not appear to remove caffeine as it passes from the gut to the general circulation), as evidenced by similar plasma concentration curves when administered by either oral or intravenous routes [ 123]. Caffeine absorption from food and beverages does not seem to be dependent on age, gender, genetics or disease, or the consumption of drugs, alcohol or nicotine. However, the rates of caffeine metabolism and breakdown appear to differ between individuals through both environmental and genetic influences [ 3, 124, 125].

Over 95% of caffeine is metabolized in the liver by the Cytochrome P450 1A2 (CYP1A2) enzyme, a member of the cytochrome P450 mixed-function oxidase system, which metabolizes and detoxifies xenobiotics in the body [ 126]. CYP1A2 catalyzes the demethylation of caffeine into the primary metabolites paraxanthine (1,7-dimethylxanthine), theobromine (3,7-dimethylxanthine) and theophylline (1,3-dimethylxanthine), which account for approximately 84, 12, and 4%, of total caffeine elimination, respectively [ 127, 128]. These three caffeine metabolites undergo further demethylations and oxidation to urates in the liver with about 3-5% remaining in caffeine form when excreted in the urine [ 129, 130]. While the average half-life (t 1/2) of caffeine is generally reported to be between 4 and 6 h, it varies between individuals and even may range from 1.5 to 10 h in adults [ 120]. The wide range of variability in caffeine metabolism is due to several factors. The rate of caffeine metabolism may be inhibited or decreased with pregnancy or use of hormonal contraceptives [ 125], increased or induced by heavy caffeine use [ 131] cigarette smoking [ 132] or modified in either direction by certain dietary factors [ 133] and/or variation in the CYP1A2 gene, which will be discussed later [ 125, 132- 134].

Several studies have also shown that the form of caffeine or its vehicle for entry into the body can modify the pharmacokinetics [ 58, 81, 119, 122]. One small trial ( n = 3) evaluated T max for a variety of beverages that all included 160 mg of caffeine but in different volumes of solution, and reported that T max occurs at 0.5, 0.5, and 2 h for coffee, tea and cola, respectively [ 135]. In another study involving seven participants, caffeine plasma concentrations peaked rapidly at 30 min for capsule form, whereas caffeine absorption from cola and chocolate was delayed and produced lower plasma concentrations that peaked at roughly 90-120 min after consumption. This study also did not control for volume of administered solution (capsules and chocolate ingested with 360 ml water and 800 ml cola) [ 122]. Liguori et al. [ 136] evaluated a 400 mg dose of caffeine in 13 subjects and reported salivary caffeine T max values of 42, 39 and 67 min, for coffee, sugar-free cola and caffeine capsules, respectively. However, fluid volume was again not standardized (coffee - 12 oz., sugar-free cola - 24 oz., capsules - volume of administered fluid not reported). The impact of temperature or rate of ingestion of caffeine has also been investigated, amidst concerns that cold energy drinks might pose a danger when chugged quickly, compared to sipping hot coffee. One study [ 121] compared five conditions that included: slow ingestion (20 min) of hot coffee, and fast (2-min) or slow (20-min) ingestion for both cold coffee and energy drinks. Similar to other caffeine pharmacokinetic studies [ 122, 135], White et al. [ 121] reported that although the rate of consumption, temperature, and source (coffee vs. energy drink) may be associated with slight differences in pharmacokinetic activity, these differences are small.

Chewing gum formulations appear to alter pharmacokinetics, as much of the caffeine released from the gum through mastication can be absorbed via the buccal cavity, which is considered faster due to its extensive vascularization, especially for low molecular weight hydrophobic agents [ 137]. Kamimori et al. [ 58] compared the rate of absorption and relative caffeine bioavailability from chewing gum compared to a capsule form of caffeine. Although caffeine administered in the chewing gum formulation was absorbed at a significantly faster rate, the overall bioavailability was comparable to the capsuled 100 and 200 mg caffeine dose groups. These pharmacokinetic findings are useful for military and sport purposes, where there is a requirement for rapid and maintained stimulation over specific periods of time. Chewing gum may also be advantageous due to reduced digestive requirements, where absorption of caffeine in other forms (capsule, coffee etc.) may be hindered by diminished splanchnic blood flow during moderate to intense exercise. Finally, there is a growing prevalence of caffeinated nasal and mouth aerosols administered directly in the mouth, under the tongue or inspired may affect the brain more quickly through several proposed mechanisms [ 5], although there are only a few studies to date to support this claim. The administration of caffeine via aerosol into the oral cavity appears to produce a caffeine pharmacokinetic profile comparable to the administration of a caffeinated beverage [ 81]. Nasal and mouth aerosols will be discussed further in another section.

Mechanism of Action (MOA)

Although the action of caffeine on the central nervous system (CNS) has been widely accepted as the primary mechanism by which caffeine alters performance, several mechanisms have been proposed to explain the ergogenic effects of caffeine, including increased myofibrillar calcium availability [ 138, 139], optimized exercise metabolism and substrate availability [ 45], as well as stimulation of the CNS [ 140- 142]. One of the earlier proposed mechanisms associated with the ergogenic effects of caffeine stemmed from the observed adrenaline (epinephrine)-induced enhanced free-fatty acid (FFA) oxidation after caffeine ingestion and consequent glycogen sparing, resulting in improved endurance performance [ 18, 45, 143]. However, this substrate-availability hypothesis was challenged and eventually dismissed, where after several performance studies it became clear that the increased levels of FFAs appeared to be higher earlier in exercise when increased demand for fuel via fat oxidation would be expected [ 141, 144, 145]. Furthermore, this mechanism could not explain the ergogenic effects of caffeine in short duration, high-intensity exercise in which glycogen levels are not a limiting factor. Importantly, several studies employing a variety of exercise modalities and intensities failed to show a decrease in respiratory exchange ratio (RER) and/or changes in serum FFAs, which would be indicative of enhanced fat metabolism during exercise when only water was ingested [ 144, 146- 148]. Ingestion of lower doses of caffeine (1-3 mg/kg of body mass), which do not result in significant physiological responses (i.e. RER, changes in blood lactate, glucose), also appear to deliver measurable ergogenic effects, offering strong support for the CNS as the origin of reported improvements [ 43, 149, 150]. As such, focus has shifted to the action of caffeine during exercise within the central and peripheral nervous systems, which could alter the rate of perceived exertion (RPE) [ 151- 154], muscle pain [ 151, 155- 157], and possibly the ability of skeletal muscle to generate force [ 151].

Caffeine does appear to have some direct effects on muscle which may contribute to its ergogenicity. The most likely pathway that caffeine may benefit muscle contraction is through calcium ion (Ca ²⁺) mobilization, which facilitates force production by each motor unit [ 138, 139, 150, 158]. Fatigue caused by the gradual reduction of Ca ²⁺ release may be attenuated after caffeine ingestion [ 139, 159]. Similarly, caffeine may work, in part, in the periphery through increased sodium/potassium (Na⁺/K⁺) pump activity to potentially enhance excitation-contraction coupling necessary for muscle contraction [ 160]. Caffeine appears to employ its effects at various locations in the body, but the most robust evidence suggests that the main target is the CNS, which is now widely accepted as the primary mechanism by which caffeine alters mental and physical performance [ 141]. Caffeine is believed to exert its effects on the CNS via the antagonism of adenosine receptors, leading to increases in neurotransmitter release, motor unit firing rates, and pain suppression [ 151, 155- 157, 161]. There are four distinct adenosine receptors, A ₁, A 2A, A 2B and A ₃, that have been cloned and characterized in several species [ 162]. Of these subtypes, A ₁ and A 2A, which are highly concentrated in the brain, appear to be the main targets of caffeine [ 163]. Adenosine is involved in numerous processes and pathways, and plays a crucial role as a homeostatic regulator and neuromodulator in the nervous system [ 164]. The major known effects of adenosine are to decrease the concentration of many CNS neurotransmitters, including serotonin, dopamine, acetylcholine, norepinephrine and glutamate [ 163- 165]. Caffeine, which has a similar molecular structure to adenosine, binds to adenosine receptors after ingestion and therefore increases the concentration of these neurotransmitters [ 163, 165]. This results in positive effects on mood, vigilance, focus, and alertness in most, but not all, individuals [ 166, 167].

Researchers have also characterized aspects of adenosine A 2A receptor function related to cognitive processes [ 168] and motivation [ 169, 170]. In particular, several studies have focused on the functional significance of adenosine A 2A receptors and the interactions between adenosine and dopamine receptors, in relation to aspects of behavioral activation and effort-related processes [ 168- 171]. The serotonin receptor 2A (5-HT2A) has also been shown to modulate dopamine release, through mechanisms involving regulation of either dopamine synthesis or dopaminergic neuron firing rate [ 172, 173]. Alterations in 5-HTR2A receptors may therefore affect dopamine release and upregulation of dopamine receptors [ 174, 175]. A possible mechanism for caffeine's ergogenicity may involve variability in 5-HTR2A receptor activity, which may modulate dopamine release and consequently impact alertness, pain and motivation and effort [ 141]. 5-HTR2A receptors are encoded by the HTR2A gene, which serves as a primary target for serotonin signaling [ 176], and variations in the gene have been shown to affect 5-HTR2A receptor activity [ 177, 178]. This may therefore modulate dopamine activity, which may help to elucidate some of the relationships among neurotransmitters, genetic variation and caffeine response, and the subsequent impact on exercise performance.

Muscle pain has been shown to negatively affect motor unit recruitment and skeletal muscle force generation proportional to the subjective scores for pain intensity [ 179, 180]. In one study, progressively increased muscle pain intensity caused a gradual decrease in motor firing rates [ 179]. However, this decrease was not associated with a change in motor unit membrane properties demonstrating a central inhibitory motor control mechanism with effects correlated to nociceptive activity [ 179]. Other studies also indicate that muscle force inhibition by muscle pain is centrally mediated [ 181]. Accordingly, caffeine-mediated CNS mechanisms, such as dopamine release [ 182], are likely imputable for pain mitigation during high-intensity exercise [ 155- 157, 181, 183- 186]. Although there appears to be strong evidence supporting the analgesic effects of caffeine during intense exercise, others have found no effect [ 185, 187].

The attenuation of pain during exercise as a result of caffeine supplementation may also result in a decrease in the RPE during exercise. Two studies [ 183, 184] have reported that improvements in performance were accompanied by a decrease in pain perception as well as a decrease in RPE under caffeine conditions, but it is unclear which factor may have contributed to the ergogenic effect. Acute caffeine ingestion has been shown to alter RPE, where effort may be greater under caffeine conditions, yet it is not perceived as such [ 12, 152- 154]. A meta-analysis [ 12] identified 21 studies using mostly healthy male subjects (74%) between the ages of 20 and 35 years and showed a 5.6% reduction in RPE during exercise following caffeine ingestion. An average improvement in performance of 11% was reported across all exercise modalities. This meta-analysis established that reductions in RPE explain up to 29% of the variance in the improvement in exercise performance [ 12]. Others have not found changes in RPE with caffeine use [ 187]. A more recent study by Green et al. [ 188] also showed that when subjects were instructed to cycle at specific RPE (effort) levels under caffeine conditions, the higher perceived intensity did not necessarily result in greater work and improved performance in all subjects equally. The authors noted that individual responses to caffeine might explain their unexpected findings.

In the last decade, our understanding of CNS fatigue has improved. Historically, it is well- documented that "psychological factors" can affect exercise performance and that dysfunction at any step in the continuum from the brain to the peripheral contractile machinery will result in muscular fatigue [ 189, 190]. The role of the CNS and its 'motor drive' effect was nicely shown by Davis et al. [ 191] who examined the effect of caffeine injected directly into the brains of rats on their ability to run to exhaustion on a treadmill. In this controlled study, rats were injected with either vehicle (placebo), caffeine, 5′-N-Ethylcarboxamido adenosine (NECA), an adenosine receptor agonist, or caffeine NECA together. Rats ran 80 min in the placebo trial, 120 min in the caffeine trial and only 25 min with NECA. When caffeine and NECA were given together, the effects appeared to cancel each other out, and run time was similar to placebo. When the study was repeated with peripheral intraperitoneal (body cavity) injections instead of brain injections, there was no effect on run performance. The authors concluded that caffeine increased running time by delaying fatigue through CNS effects, in part by blocking adenosine receptors [ 191]. Caffeine also appears to enhance cognitive performance more in fatigued than well-rested subjects [ 192- 194]. This phenomenon is also apparent in exercise performance [ 195] both in the field [ 196] and in the lab [ 60, 63, 149].

The placebo effect

The placebo effect is a beneficial outcome that cannot be attributed to a treatment or intervention but is brought about by the belief that one has received a positive intervention. For example, an individual may ingest a capsule with sugar or flour (a small amount of non-active ingredient) but believes that he/she ingested caffeine and experiences improvements in performance because of this belief [ 197]. The nocebo effect is directly opposite to this in that a negative outcome occurs following the administration of an intervention or lack of an intervention (e.g. knowingly ingesting a placebo) [ 198]. For example, the nocebo may be a substance without medical effects, but which worsens the health status of the person taking it by the negative beliefs and expectations of the patient. Similarly, the nocebo may be a 'caffeine placebo', where an individual's performance is worse based on the belief that they did not ingest caffeine.

Several studies have provided evidence for placebo effects associated with caffeine ingestion [ 199- 201] or other "beneficial" interventions [ 202] during exercise. An example of this was reported in a study [ 200] where well-trained cyclists exhibited a linear dose-response relationship in experimental trials from baseline to a moderate (4.5 mg/kg) and high dose (9 mg/kg) of caffeine respectively. Athletes improved as the perceived caffeine doses increased; however, a placebo was used in all interventions. Similarly, Saunders et al. [ 201] found that correct identification of caffeine appears to improve cycling performance to a greater extent than the overall effect of caffeine, where participants who correctly identified placebo showed possible harmful effects on performance. Therefore, readers are encouraged to consider whether studies that have explored the effects of caffeine on exercise have examined and reported the efficacy of the blinding of the participants.

Caffeine and endurance exercise

Less than a 1% change in average speed is enough to affect medal rankings in intense Olympic endurance events lasting ~ 45 s to 8 min [ 203]. In other events, such as the men's individual road race, the difference between the top three medalists was < 0.01% [ 204]. At the highest level of sports, competitors will be near their genetic potential, will have trained intensively, followed prudent recovery protocols, and will have exploited all strategies to improve their performance-the use of an ergogenic aid, when legal, safe and effective, is an alluring opportunity.

Caffeine has consistently been shown to improve endurance by 2-4% across dozens of studies using doses of 3-6 mg/kg body mass [ 13, 195, 205- 207]. Accordingly, caffeine is one of the most prominent ergogenic aids and is used by athletes and active individuals in a wide variety of sports and activities involving aerobic endurance. Caffeine has been shown to benefit several endurance-type sports including cycling [ 60, 206, 208], running [ 91, 209, 210] cross-country skiing [ 211] and swimming [ 212].

Much of the caffeine-exercise body of literature has focused on endurance-type exercise, as this is the area in which caffeine supplementation appears to be more commonly used and likely beneficial in most, but not all, athletes [ 11- 13]. For example, the caffeine concentration in over twenty thousand urine samples obtained for doping control from 2004 to 2008 was measured after official national and international competitions [ 110, 115]. The investigations concluded that roughly 74% of elite athletes used caffeine as an ergogenic aid prior to or during a sporting event, where endurance sports are the disciplines showing the highest urine caffeine excretion (and therefore prevalence) after competition [ 110, 115].

A recent meta-analysis reporting on 56 endurance time trials in athletes (79% cycling), found the percent difference between the caffeine and placebo group ranged from − 3.0 to 15.9% [ 195]. This wide range in performance outcomes highlights the substantial inter-individual variability in the magnitude of caffeine's effects as reported. These inter-individual differences might be due to the methodological differences between the studies, habitual caffeine intake of the participants, and/or partly due to variation in genes that are associated with caffeine metabolism and caffeine response [ 213].

A recent systematic review was carried out on randomised placebo-controlled studies investigating the effects of caffeine on endurance performance and a meta-analysis was conducted to determine the ergogenic effect of caffeine on endurance time-trial performance [ 205]. Forty-six studies met the inclusion criteria and were included in the meta-analysis. This meta-analysis found that caffeine has a small but significant effect on endurance performance when taken in moderate doses (3-6 mg/kg) as well as an overall improvement following caffeine compared to placebo in mean power output of 2.9 ± 2.2% and a small effect size of 0.22 ± 0.15. Time-trial completion time showed improvements of 2.3 ± 2.6% with a small effect size of 0.28 ± 0.12. However, there was some variability in outcomes with responses to caffeine ingestion, with two studies reporting slower time-trial performance, and five studies reporting lower mean power output during the time-trial [ 205].

In summary, caffeine has been consistently shown to be effective as an ergogenic aid when taken in moderate doses (3-6 mg/kg), during endurance-type exercise and sport. Dozens of endurance studies are highlighted through this review is various sections, showing consistent yet wide-ranging magnitudes of benefit for endurance performance under caffeine conditions.

Caffeine and muscular endurance, strength and power

Strength and power development through resistance exercise is a significant component of conditioning programs for both fitness and competitive sport. The most frequently consumed dose of caffeine in studies using strength tasks with trained or untrained individuals usually ranges from 3 to 6 mg/kg body mass (with 2 mg to 11 mg representing the entire range), ingested in the form of pills or capsules 30 to 90 min before exercise. In resistance exercise, strength is most commonly assessed using 1 repetition maximum (1RM) [ 214], or different isometric and isokinetic strength tests [ 215]. Muscular endurance assesses the muscle's ability to resist fatigue and is an important quality in many athletic endeavors (e.g., swimming, rowing). Muscular endurance may be tested with repetitions of squats, maximal push-ups, bench press exercises (load corresponding to 60-70% of 1RM) to momentary muscular failure, or by isometric exercises such as the plank or static squat [ 216, 217].

Although several studies exploring the effects of caffeine on strength performance have been published since the 2010 ISSN caffeine position stand [ 40], some uncertainty surrounding the benefits of caffeine in activities involving muscular endurance, strength and power remains.

Caffeine was shown to be ergogenic for muscular endurance in two meta-analyses reporting effect sizes ranging from 0.28 to 0.38 (percent change range: 6 to 7%) [ 158, 218]. However, others have shown that it enhances strength but not muscular endurance [ 219, 220], and when studies have examined multiple strength-muscular endurance tasks, there were benefits across the board [ 67, 221], none at all [ 98, 222], or even impairments in muscular endurance with caffeine use [ 222, 223]. Ingesting caffeine prior to a muscular endurance task is likely to delay muscular fatigue, but these effects are not consistent among all studies.

Three meta-analyses explored the acute effects of caffeine on strength, and all reported ergogenic effects [ 158, 224, 225]. However, the effects in these meta-analyses were small, ranging from 0.16 to 0.20 (percent change: 2 to 7%). Such small improvements in muscular strength likely have the greatest practical meaningfulness for athletes competing in strength-based sports, such as powerlifting and weightlifting (athletes which already seem to be among the highest users of caffeine [ 110]).

Power output is often measured during a single-bout sprinting task using the Wingate test, which generally consists of 'all-out' cycling for 30 s performed at specific external loads (e.g., 7.5% of body mass). Power output is also assessed during different protocols of intermittent-sprinting and repeated-sprints often with the Wingate cycling test as well as assessments during running [ 226] or swimming repeated sprints [ 212].

The data for repeated sprint and power performance using Wingate data has been mixed. In an older study, 10 male team-sport athletes performed 18, 4-s sprints with 2-min active recovery [ 227]. Here, caffeine ingestion (6 mg/kg) enhanced mean power output and sprint work by 7 and 8.5%, respectively [ 227]. A more recent study examining the effects of acute caffeine ingestion on upper and lower body Wingate performance in 22 males did not report significant findings when measuring lower body mean and peak power using the Wingate test [ 228]. An older study by Greer et al. [ 229] also failed to report caffeine benefits on power output during a 30-s high-intensity cycling bout using the Wingate test. One meta-analysis reported that caffeine ingestion enhances mean and peak power during the Wingate test [ 230], although the effect sizes of 0.18 (+ 3%) and 0.27 (+ 4%), respectively are modest. In contrast, another meta-analysis that examined the effects of caffeine on muscle power as assessed with the Wingate test for three of the studies, and repeated sprints for a maximum of 10-s for the fourth, did not report benefits from ingestion of caffeine [ 231]. An average caffeine dose of 6.5 mg/kg of body mass was used across the four studies with no improvements in muscle power under caffeine conditions (effect size = 0.17, p = 0.36) compared to placebo trials, although the data collected spanned only 5 years [ 231]. A study by Lee et al. [ 232] reported that caffeine ingestion enhanced sprint performance involving a 90-s rest interval (i.e., intermittent-sprinting) but did not benefit repeated-sprints with a 20-s rest interval. This might suggest that the rest interval between sprints may modulate the ergogenic effects of caffeine. Indeed, a recent meta-analysis that focused on the effects of caffeine on repeated-sprint performance reported that total work, best sprint, and last sprint performance was not affected by caffeine ingestion [ 226].

Several studies have also shown substantial variability in outcomes. For example, one study [ 63] found that only 13 of 20 cyclists improved their performance with ~ 3-4 mg/kg of caffeine, while the remaining participants either worsened or did not alter their performance. Similarly, Woolf et al. [ 233] found that 5 mg/kg of caffeine improved overall peak power performance on the Wingate Test in 18 elite or professional athletes. However, 4 (28%) of the participants did not improve their performance with caffeine. Average power, minimum power, and power drop were not significantly different between treatments, but 72% of the participants obtained a greater peak power during the caffeine trial than during the placebo trial. There was also no overall improvement in average power or fatigue index, despite 13 (72%), and 9 (50%) of the participants, respectively, improving their performance. In summary, caffeine ingestion may be beneficial to enhance single and intermittent-sprint performance, while caffeine's effects on repeated-sprint performance are inconsistent and require further research to draw stronger conclusions on the topic.

Ballistic movements (such as throws and jumps) are characterized by high motor unit firing rates, brief contraction times, and high rates of force development [ 234]. Many studies have explored the effects of caffeine on jumping performance [ 225, 235]. The body of evidence has indicated that caffeine supplementation increases vertical jump height during single and repeated jumps; however, the magnitude of these effects is rather modest, with effect sizes ranging from 0.17 to 0.22 (2 to 4%) [ 225, 235]. Besides jumping, several studies have explored the effects of caffeine on throwing performance. These studies reported that: (a) caffeine ingestion enhanced maximal shot put throwing distance in a group of 9 nine inter-collegiate track and field athletes [ 65]; and (b) caffeine ingestion at a dose of 6 mg/kg of body mass administered 60 min pre-exercise increased maximal medicine ball throwing distance [ 236]. Overall, the current body of evidence indicates that caffeine supplementation may be useful for acute improvements in ballistic exercise performance in the form of jumps and throws. However, more research is needed to explore the effects of caffeine on different throwing exercise tests, as this has been investigated only in a few studies.

Generally, the primary sports-related goal of strength and power-oriented resistance training programs is to move the force-velocity curve to the right, indicating an ability of the athlete to lift greater loads at higher velocities [ 237]. Several studies have explored the effects of caffeine on movement velocity and power in resistance exercise using measurement tools such as linear position transducers [ 238]. These studies generally report that caffeine ingestion provides ergogenic effects of moderate to large magnitudes, with similar effects noted for both mean and peak velocity, and in upper and lower-body exercises [ 67, 221, 239]. Even though this area merits further research to fill gaps in the literature, the initial evidence supports caffeine as an effective ergogenic aid for enhancing velocity and power in resistance exercise.

Caffeine and sport-specific performance

Even though caffeine ingestion may enhance performance in the laboratory, there has been a paucity of evidence to support that these improvements transfer directly to sport-specific performance. To address this issue, several studies have also explored the effects of caffeine on sport-specific exercise tasks using sport simulation matches. Many studies conducted among athletes competing in team and individual sports, report that caffeine may enhance performance in a variety of sport tasks. However, there are also several studies that report no effects as outlined below:

Basketball - increased jump height, but only in those with the AA version of the CYP1A2 gene [ 240], increased number of free throws attempted and free throws made, increased number of total and offensive rebounds [ 241], but did not improve sprint time [ 240], nor dribbling speed [ 242]

Soccer - increased total distance covered during the game, increased passing accuracy, and jumping height [ 94, 243, 244], but the consumption of a caffeinated energy drink did not enhance performance in the "T test" in female soccer players [ 245], nor during match play in young football players [ 246]

Volleyball - increased number of successful volleyball actions and decreased the number of imprecise actions [ 247, 248], although caffeine did not improve physical performance in multiple sport-specific tests in professional females [ 249], nor performance in volleyball competition [ 250]

Football - did not improve performance for anaerobic exercise tests used at the NFL Combine [ 251]

Rugby - increased the number of body impacts, running pace, and muscle power during jumping [ 252, 253], but did not impact agility [ 254]

Field hockey - increased high-intensity running and sprinting [ 255], and may offset decrements in skilled performance associated with fatigue [ 256]

Ice-hockey - has limited impact on sport-specific skill performance and RPE, but may enhance physicality during scrimmage [ 257]

Combat sports - increased number of offensive actions and increased the number of throws [ 258]

Cross-country skiing - reduced time to complete a set distance [ 259] and improved time to task failure [ 211]

In summary, although reviews of the literature show that caffeine ingestion is, on average, ergogenic for a wide range of sport-specific tasks, its use might not be appropriate for every athlete. Specifically, the use of caffeine needs to be balanced with the associated side-effects and therefore experimentation is required in order to determine the individual response before assessing whether the benefits outweigh the costs for the athlete. Athletes should gauge their physical response to caffeine during sport practice and competition in addition to monitoring mood state and potentially disrupted sleep patterns.

Interindividual variation in response to caffeine

There is a lack of research examining potential interindividual differences in strength or anaerobic power-type exercise, but this is not the case for endurance exercise. In the myriad of studies examining caffeine on endurance performance, the benefits of caffeine do not appear to be influenced by sex, age, VO ₂ max, type of sport, or the (equivalent) dose of caffeine [ 13, 195, 260]. Nevertheless, there appears to be substantial interindividual variability in response to caffeine under exercise conditions, which may be attributed to several factors outlined below.

Genetics

Genetic variants affect the way we absorb, metabolize, and utilize and excrete nutrients, and gene-diet interactions that affect metabolic pathways relevant to health and performance are now widely recognized [ 261]. In the field of nutrigenomics, caffeine is the most widely researched compound with several randomized controlled trials investigating the modifying effects of genetic variation on exercise performance [ 75, 208, 262, 263].

Numerous studies have investigated the effect of supplemental caffeine on exercise performance, but there is considerable inter-individual variability in the magnitude of these effects [ 11, 13, 44] or in the lack of an effect [ 264, 265], when compared to placebo. Due to infrequent reporting of individual data it is difficult to determine the extent to which variation in responses may be occurring. The performance of some individuals is often in stark contrast to the average findings reported, which may conclude beneficial, detrimental, or no effect of caffeine on performance. For example, Roelands et al. [ 265] reported no ergogenic effect of caffeine in a study involving trained male cyclists. The authors concluded that inter-individual differences in response to caffeine might be responsible for the lack of overall performance improvement, as 50% of subjects improved while 50% worsened, in the caffeine compared to the placebo trial.

These inter-individual differences appear to be partly due to variations in genes such as CYP1A2 and possibly ADORA2A, which are associated with caffeine metabolism, sensitivity and response [ 213]. Over 95% of caffeine is metabolized by the CYP1A2 enzyme, which is encoded by the CYP1A2 gene and is involved in the demethylation of caffeine into the primary metabolites paraxanthine, theophylline and theobromine [ 127]. The -163A > C (rs762551) single nucleotide polymorphism (SNP) has been shown to alter CYP1A2 enzyme inducibility and activity [ 132, 134], and has been used to categorize individuals as 'fast' or 'slow' metabolizers of caffeine. In the general population, individuals with the AC or CC genotype (slow metabolizers) have an elevated risk of myocardial infarction [ 266], hypertension and elevated blood pressure [ 267, 268], and pre-diabetes [ 269], with increasing caffeinated coffee consumption, whereas those with the AA genotype show no such risk. Additionally, regular physical activity appears to attenuate the increase in blood pressure induced by caffeine ingestion, but only in individuals with the AA genotype [ 268].

The largest caffeine, genetics and exercise study to date [ 208] examined the effects of caffeine and CYP1A2 genotype on 10-km cycling time trial performance in competitive male athletes (both endurance and power sports) after ingestion of placebo, and caffeine doses of 2 mg (low dose) or 4 mg (moderate dose) per kg body mass. There was a 3% improvement in cycling time with the moderate dose in all subjects, which is consistent with previous studies using similar doses [ 13, 206]. However, there was a significant caffeine-gene interaction; improvements in performance were seen at both caffeine doses, but only in those with the AA genotype who are 'fast metabolizers' of caffeine. In that group, a 6.8% improvement in cycling time was observed at 4 mg/kg, which is greater than the 2-4% mean improvement seen in several other studies using cycling time trials and similar doses [ 13, 201, 206, 207, 270- 272]. Among those with the CC genotype (i.e., "slow metabolizers"), 4 mg/kg caffeine impaired performance by 13.7%, whereas no difference was observed between the placebo and 2 mg/kg caffeine trials. In those with the AC genotype there was no effect of either dose [ 208]. The findings are consistent with a previous study [ 263] that observed a caffeine-gene interaction indicating improved time trial cycling performance following caffeine consumption only in those with the AA genotype.

In contrast, previous studies either did not observe any impact of the CYP1A2 gene in caffeine-exercise studies [ 273, 274], or reported benefits only in slow metabolizers [ 75]. There are several reasons that may explain discrepancies in study outcomes. These include smaller samples sizes with few and/or no subjects in one genotype [ 75, 273, 274], as well as shorter distances or different types of performance test (power versus endurance) [ 75] compared to the aforementioned trials, which reported improved endurance after caffeine ingestion in those with the CYP1A2 AA genotype [ 208, 263]. The effects of genotype on performance might be the most prominent during training or competition of longer duration or an accumulation of fatigue (aerobic or muscular endurance) [ 149], where caffeine appears to provide its greatest benefits, and where the adverse effects to slow metabolizers are more likely to manifest [ 195, 260]. Indeed, in a study of performance in elite basketball players [ 240], only in those with the AA genotype caffeine improved repeated jumps which requires maintaining velocity at take-off repeatedly as an athlete fatigues throughout a game (muscular endurance) - even though there was no caffeine-genotype interaction effect for this outcome. However, caffeine similarly improved performance in those with the both AA and C-genotypes during a simulated basketball game [ 240]. In a cross-over design of 30 resistance-trained men, caffeine ingestion resulted in a higher number of repetitions in repeated sets of three different exercises, and for total repetitions in all resistance exercises combined, which resulted in a greater volume of work compared to placebo conditions, but only in those with the CYP1A2 AA genotype [ 262]. Although more research is warranted, there is a growing body of evidence to support the role of CYP1A2 in modifying the effects of caffeine ingestion on aerobic or muscular endurance-type exercise, which helps to determine which athletes are most likely to benefit from caffeine.

The ADORA2A gene is another genetic modifier of the effects of caffeine on performance. The adenosine A 2A receptor, encoded by the ADORA2A gene, has been shown to regulate myocardial oxygen demand and increase coronary circulation by vasodilation [ 275, 276]. The A 2A receptor is also expressed in the brain, where it has significant roles in the regulation of glutamate and dopamine release, with associated effects on insomnia and pain [ 277, 278]. The antagonism of adenosine receptors after caffeine ingestion is modified by the ADORA2A gene, which may allow greater improvements in dopamine transmission and lead to norepinephrine and epinephrine release due to increased neuronal firing [ 168] in some genotypes versus others. Dopamine has been associated with motivation and effort in exercising individuals, and this may be the mechanism by which differences in response to caffeine are manifested [ 141, 168, 169].

Currently, only one small pilot study has examined the effect of the ADORA2A gene (rs5751876) on the ergogenic effects of caffeine under exercise conditions [ 279]. Twelve female subjects underwent a double-blinded, crossover trial comprising two 10-min cycling time trials following caffeine ingestion or placebo. Caffeine benefitted all six subjects with the TT genotype, but only one of the six C allele carriers. Further studies are needed to confirm these preliminary findings and should include a large enough sample to distinguish any effects between the different C allele carriers (i.e. CT vs. CC genotypes) and potential effects related to sex.

The ADORA2A rs5751876 genotype has also been implicated, by both objective and subjective measures, in various parameters of sleep quality after caffeine ingestion in several studies [ 280- 283]. Adenosine promotes sleep by binding to its receptors in the brain, mainly A ₁ and A 2A receptors, and caffeine exerts an antagonist effect, blocking the receptor and reversing the effects of adenosine and promoting wakefulness [ 280]. This action, as well as the potency of caffeine to restore performance (cognitive or physical) in ecological situations, such as highway-driving during the night [ 284], supports the notion that the adenosine neuromodulator/receptor system is significantly involved in sleep-wake regulation. This action of caffeine may also serve athletes well under conditions of jetlag, and irregular or early training or competition schedules. Psychomotor speed relies on the ability to respond, rapidly and reliably, to randomly occurring stimuli which is a critical component of, and characteristic of, most sports [ 285]. Genetic variation in ADORA2A has been shown to be a relevant determinant of psychomotor vigilance in the rested and sleep-deprived state and modulates individual responses to caffeine after sleep deprivation [ 282]. Those with the CC genotype of ADORA2A rs5751876 consistently performed on a higher level on the sustained vigilant attention task than T-allele -carriers; however, this was tested in ADORA2A haplotypes that included combinations of 8 SNPs. This work provides the basis for future genetic studies of sleep using individual ADORA2A SNPs.

As mentioned, the ADORA2A genotype has also been implicated in sleep quality and increases in sleep disturbance [ 283]. Consistent with the "adenosine hypothesis" of sleep where the accumulation of adenosine in the brain increases sleep propensity, caffeine prolongs time to fall asleep, decreases the deep stages of non-rapid-eye movement (nonREM) sleep, reduces sleep efficiency, and alters the waking and sleep electroencephalogram (EEG) frequencies, which reliably reflect the need for sleep [ 286- 288]. Increased beta activity in nonREM sleep may characterize individuals with insomnia when compared with healthy good sleepers [ 289]. A functional relationship between the ADORA2A genotype and the effect of caffeine on EEG beta activity in nonREM sleep has previously been reported [ 281], where the highest rise was in individuals with the CC genotype, approximately half in the CT genotype, whereas no change was present in the TT genotype. Consistent with this observation, the same study found individuals with the CC and TC genotypes appeared to confer greater sensitivity towards caffeine-induced sleep disturbance compared to the TT genotype [ 281]. This suggests that a common variant in ADORA2A contributes to subjective and objective responses to caffeine on sleep.

Caffeine, genetics and anxiety

In elite athletes, 50% face mental health issues sometime during their career [ 290]. Given that anxiety may be normalized in elite sports even at clinical levels, factors that contribute to anxiety should be mitigated whenever possible. Anxiety may be caused by stress-related disorders (burnout), poor quality sleep patterns (often related to caffeine intakes) and possibly as a response to caffeine ingestion due to genetic variation, even at low levels [ 109].

As previously mentioned, caffeine blocks adenosine receptors, resulting in the stimulating effects of caffeine [ 213]. A common variation in the ADORA2A (adenosine A 2A receptor) gene contributes to the differences in subjective feelings of anxiety after caffeine ingestion [ 291, 292], especially in those who are habitually low caffeine consumers [ 293]. This may be particularly relevant to athletes who possess the TT variant of rs5751876 in the ADORA2A gene. These individuals are likely to be more sensitive to the stimulating effects of caffeine and experience greater increases in feelings of anxiety after caffeine intake than do individuals with either the CT or CC variant [ 291- 293].

Sport psychologists commonly work with athletes to help them overcome anxiety about performance during competitions. Anxiety before or during athletic competitions can interfere not only in performance, but also in increased injury risk [ 294]. Athletes who are more prone to performance anxiety may exacerbate their risk for feelings of anxiety depending on their caffeine use and which variant of the ADORA2A gene they possess. Monitoring the actions of caffeine in those individuals who are susceptible, may alleviate some of the related feelings of anxiety with caffeine use. Given that anxiety may disrupt concentration and sleep and negatively impact social interactions, athletes with higher risks and prevalence for anxiety, may want to limit or avoid caffeine consumption (if caffeine is a known trigger) during times where they are feeling anxious or stressed, such as at sporting competitions or social gatherings or other work and school events.

The importance of both sleep and caffeine (as an ergogenic aid) to athletes highlights the importance of optimizing rest and recovery through a better understanding of which athletes may be at greater risk of adverse effects of caffeine on mood and sleep quality, possibly due to genetic variation. This information will allow athletes and coaching staff to make informed decisions on when and if to use caffeine when proximity to sleep is a factor. These considerations will also be in conjunction with the possibility that an athlete will benefit from caffeine in endurance-based exercise as determined in part, by their CYP1A2 genotype, albeit with a clear need for future research.

Habitual caffeine intake

The quantification of habitual caffeine intake is difficult, which is problematic for studies aiming to compare performance outcomes following caffeine ingestion in habitual versus non-habitual caffeine users. This concern is highlighted by reports showing large variability in the caffeine content of commonly consumed beverages, e.g. ~ 8- to 9-fold differences in caffeine content have been reported in coffee beverages purchased from similar retail shops [ 295] and in pre-workout supplements [ 296]. Self-reported intakes may therefore be unreliable. Newly discovered biomarkers of coffee consumption may be more useful for quantifying intakes in the future, but currently, these are not widely available [ 297]. Different protocols for the length of the caffeine abstinence period preceding data collection is also a relevant factor in determining variability in performance outcomes. For example, in shorter caffeine abstinence periods e.g., 12-48 h, reversal of caffeine withdrawal effects by acute caffeine supplementation may have positive effects on performance, i.e. alleviating the negative symptoms of withdrawal, which in itself may improve performance [ 298]. These effects may be more pronounced in those genetically predisposed to severe withdrawal effects [ 299]. However, in one study 3 mg/kg caffeine significantly improved exercise performance in trained cyclists ( n = 12), irrespective of whether a 4-day withdrawal period was imposed on habitual caffeine users [ 300]. Another study also reported increased endurance in habitual caffeine users ( n = 6) regardless of a 0, 2- or 4-day abstinence period. The authors concluded that improved performance under caffeine conditions at 6 mg/kg is not related to prior caffeine habituation in recreational athletes [ 301]. Although genes have been associated with habitual caffeine intake using GWAS research [ 302, 303], it is important to highlight that these associations are not directly applicable to determining differences in performance outcomes in response to acute caffeine doses for regular or habitual caffeine users versus non-habitual users. The "caffeine habits" of individuals are more likely related to their personal experience with adverse effects such as feel jittery, experiencing tachycardia or insomnia. Furthermore, associations between genes and habitual caffeine intake do not elucidate potential mechanisms by which caffeine intake behaviors may influence subsequent performance following caffeine supplementation [ 304, 305]. In animal model studies, regular consumption of caffeine has been associated with an upregulation of the number of adenosine receptors in the vascular and neural tissues of the brain [ 306]. Although, this did not appear to modify the effects of caffeine in one study [ 307], in another, chronic caffeine ingestion by mice caused a marked reduction in locomotor exploratory activity [ 308]. Changes in adenosine receptor number or activity have not been studied in humans.

There does not appear to be a consistent difference in the performance effects of acute caffeine ingestion between habitual and non-habitual caffeine users, and study findings remain equivocal. In one study, habitual stimulation from caffeine resulted in a general dampening of the epinephrine response to both caffeine and exercise; however, there was no evidence that this impacted exercise performance [ 309]. Another study [ 310] examined the effect of 4 weeks of caffeine supplementation on endurance performance in 18 low-habitual caffeine consumers who were randomly assigned to ingest caffeine or placebo for 28 days. Four weeks of caffeine ingestion resulted in increased tolerance to acute caffeine supplementation in previously low habitual caffeine consumers, with the ergogenic effect of acute caffeine supplementation no longer apparent [ 310]. These results are in contrast with a recent study in which 20 days of consecutive supplementation with caffeine maintained an ergogenic effect, even though the effect size attenuated over time [ 311]. More recently, a double-blind, crossover, counterbalanced study was performed [ 312], where 40 endurance-trained male cyclists were allocated into tertiles according to their daily caffeine intake: low (58 ± 29 mg), moderate (143 ± 25 mg), and high consumers (351 ± 139 mg). Participants completed three trials in which they performed simulated cycling time-trials under three conditions: caffeine (6 mg/kg), placebo, and no supplement (control). Caffeine ingestion improved performance as compared to placebo and control, with no influence of habitual caffeine intake. Additionally, no correlation was observed between habitual caffeine intake and absolute changes in a ~ 30 min cycling time-trial performance with caffeine [ 312]. However, a limitation of this study is the short 24-h caffeine withdrawal period in all groups which may have resulted in performance improvements due to the reversal of caffeine withdrawal effects, rather than impact of acute-on-chronic caffeine administration and the effects of habituation to caffeine on exercise performance [ 298, 313]. In addition, habitual caffeine intake was estimated using a food frequency questionnaire, which might be a limitation given the already mentioned variation of caffeine in coffee and different supplements.

There is wide variability in caffeine content of commonly consumed items, and as such, an objective measure (e.g., caffeine or metabolite levels) might be considered to reported caffeine intakes [ 297, 313]. Based on these observations, the assumption that habitual and nonhabitual caffeine consumers will or will not respond differently to caffeine supplementation during exercise, requires further study.

Caffeine timing

The most common timing of caffeine supplementation is 60 min before exercise. This timing is used given that it is believed that 60 min post-ingestion, plasma levels of caffeine are at maximal values [ 314]. However, caffeine appears to be most beneficial during times or in sports where there is an accumulation of fatigue, i.e., exercise over a longer continuous or intermittent duration [ 64]. Therefore, ingestion of caffeine during exercise (mid/later stages) may be more beneficial than ingestion beforehand for some individuals depending upon the length of the event. A recent review [ 195] reported that the effect size of caffeine benefits increase with the increasing duration of the time trial event, meaning that timing caffeine intake closer to a time of greater fatigue, i.e., later in the race, may be most beneficial. This supports the notion that endurance athletes (with longer races) may benefit most from caffeine for performance enhancement since they have the greatest likelihood of being fatigued. This also supports findings in other investigations that show ingesting caffeine at various time points including late in exercise may be most beneficial [ 196].

For example, an early study [ 196] aimed to understand whether or not there were benefits to a common practice among endurance athletes, such as those participating in marathons and triathlons, which is to drink flat cola toward the end of an event. When researchers investigated the ingestion of a low dose of caffeine toward the end of a race (e.g., in the form of flat cola) it was found to have comparable effects as ingesting higher doses, such as ~ 5 or 6 mg/kg, ingested ~ 60 min before the race. The study also demonstrated that the effect was due to the caffeine and not the carbohydrate, which may also aid performance as fuel stores become depleted [ 196].

More recently, caffeine gum ingestion enhanced cycling performance when it was administered immediately prior to exercise, but not when administered 1 or 2 h beforehand. This may have been due to the faster absorption with caffeinated gum consumption, and due to the continued increase in plasma caffeine concentrations during the cycling time trial, when athletes may become fatigued (i.e. 30 + minutes into exercise), as the trials also included a 15 min steady-state cycling bout prior to the time trial [ 60]. Similarly, in a lab setting, a study of athletes completing 120 min of steady-state cycling followed by a time trial under conditions of placebo and caffeine, found that the ingestion of both low and moderate doses of caffeine later in exercise were beneficial [ 149]. However, there was significant interindividual variability, highlighting the need for athletes to experiment with their own strategies as far as dosing and timing are concerned.

The optimal timing of caffeine ingestion may depend on the source of caffeine. As stated earlier, some of the alternate sources of caffeine such as caffeine chewing gums may absorb more quickly than caffeine ingested in caffeine-containing capsules [ 60]. Therefore, individuals interested in supplementing with caffeine should consider that timing of caffeine ingestion will likely be influenced by the source of caffeine.

Training status

Training status may mediate the magnitude of caffeine's ergogenic effect, but studies have reported mixed results. Although a 2010 meta-analysis [ 158] did not find differences ( p = 0.08) in caffeine's ability to enhance muscle endurance in untrained subjects versus trained subjects, these results were not derived from direct comparisons between trained and untrained subjects. Currently, only a few investigations [ 96, 210, 315- 318] have included both trained and untrained subjects in their study design.

In a study of elite and occasional swimmers [ 318], it was reported that 250 mg of supplemental caffeine was ergogenic only for competitive swimmers and not recreational swimmers. A limitation of this study is that the swimming exercise task differed between the trained and untrained participants. Specifically, the study utilized 1600-m swimming for the trained swimmers and 400-m for the untrained swimmers, which is a likely explanation for these findings. However, some have also postulated that this is because athletes perform more reliably on a given task than nonathletes, and increased test-retest reliability might prevent type II errors [ 319]. In contrast to the above evidence regarding the importance of training status, other research has shown that training status does not moderate the ergogenic effects of caffeine on exercise performance. One study [ 210] showed similar performance improvements (1.0 and 1.1%) in 15 well-trained and 15 recreational runners performing an outdoor 5 km time trial after 5 mg/kg caffeine intake compared to the placebo trial. Similarly, Astorino et al. [ 96] found that overall, acute caffeine intake improved 10 km time-trial performance in both endurance-trained athletes and active men, with no differences seen between groups. Likewise, an investigation concluded that there was no ergogenic effect of caffeine at a dose of 5 mg/kg on time to exhaustion in either endurance trained or untrained men [ 315].

More recently, a small study by Boyett et al. [ 317] investigated the interactions of 6 mg/kg caffeine on training status and time of day in 20 male subjects. Subjects completed four experimental trials consisting of a 3-km cycling time trial performed in randomized order for each combination of time of day (morning and evening) and treatment. They reported that both untrained and trained subjects improved performance with caffeine supplementation in the morning; however, only the untrained subjects improved when tested in the evening. Although there were some limitations to this study, these observations indicate that trained athletes are more likely to experience ergogenic effects from caffeine in the morning, while untrained individuals appear to receive larger gains from caffeine in the evening than their trained counterparts. This may further complicate the training status data with a possible temporal effect [ 317]. The concentration of adenosine receptors (the primary target of caffeine) do appear to be higher in trained compared to untrained individuals, but this has only been reported in animal studies [ 320]. Boyett et al. [ 317] speculated that the higher concentration of adenosine receptors may increase tissue sensitivity to any given concentration of adenosine.

Although some studies comparing training status of subjects support the notion [ 318] that training influences response to caffeine during exercise, most do not [ 96, 210, 315] and this was also the finding in a subsequent meta-analysis [ 158]. It is possible that the only difference between trained and untrained individuals is that trained individuals likely have the mental discipline to exercise long or hard enough to benefit more from the caffeine stimulus, which might provide an explanation for why in some studies, trained individuals respond better to caffeine [ 314]. Currently, it seems that trained and untrained individuals experience similar improvements in performance following caffeine ingestion; however, more research in this area is warranted.

Caffeine and sleep

The impacts of caffeine on sleep and behavior after sleep deprivation are widely reported [ 321]. Sleep is recognized as an essential component of physiological and psychological recovery from, and preparation for, high-intensity training in athletes [ 322, 323]. Chronic mild to moderate sleep deprivation in athletes, potentially attributed to caffeine intakes, may result in negative or altered impacts on glucose metabolism, neuroendocrine function, appetite, food intake and protein synthesis, as well as attention, learning and memory [ 323]. These factors can all influence an athlete's nutritional, metabolic, and endocrine status negatively and hence potentially affect energy levels, muscle repair, immunity, body composition, memory and learning and result in diminished athletic performance [ 324, 325].

Objective sleep measures using actigraphy or carried out in laboratory conditions with EEG have shown that caffeine negatively impacts several aspects of sleep quality such as: sleep latency (time to fall asleep), WASO (wake time after sleep onset), sleep efficiency and duration [ 321]. Studies in athletes have also shown adverse effects in sleep quality and markers for exercise recovery after a variety of doses of caffeine ingestion [ 326- 328]. Although caffeine is associated with sleep disturbances, caffeine has also been shown to improve vigilance and reaction time and improved physical performance after sleep deprivation [ 282, 329- 332]. This may be beneficial for athletes or those in the military who are traveling or involved in multiday operations, or sporting events and must perform at the highest level under sleep-deprived conditions [ 192, 194, 330, 332].

Even though caffeine ingestion may hinder sleep quality, the time of day at which caffeine is ingested will likely determine the incidence of these negative effects. For example, in one study that included a sample size of 13 participants, ingestion of caffeine in the morning hours negatively affected sleep only in one participant [ 333]. However, ingestion of caffeine in the late afternoon (18:00 h) resulted in insomnia effects among 6 participants. These results are likely explained by the half-life of caffeine, which is generally around 4 to 6 h (even though it varies between individuals). Unfortunately, athletes and those in the military are unlikely to be able to make adjustments to the timing of training, competition and military exercises or the ability to be combat ready. However, to help avoid negative effects on sleep, athletes may consider using caffeine earlier in the day whenever possible. Pronounced individual differences have also been reported where functional genetic polymorphisms have been implicated in contributing to individual sensitivity to sleep disruption [ 280, 281] and caffeine impacts after sleep deprivation [ 282] as discussed in the Interindividual variation in response to caffeine: Genetics section of this paper.

Side-effects associated with caffeine intake

As with any supplement, caffeine ingestion is also associated with certain side-effects. Some of the most commonly reported side-effects in the literature are tachycardia and heart palpitations, anxiety [ 281, 291], headaches, as well as insomnia and hindered sleep quality [ 239, 326]. For example, in one study, caffeine ingestion before an evening Super Rugby game resulted in a delay in time at sleep onset and a reduction in sleep duration on the night of the game [ 327]. Caffeine ingestion is also associated with increased anxiety; therefore, its ingestion before competitions in athletes may exacerbate feelings of anxiety and negatively impact overall performance (see caffeine and anxiety section). Increased jitters/anxiety/arousal associated with caffeine ingestion also needs to be considered within the specific demands of each sport, and even the position within a given sport. For example, athletes competing in sports that heavily rely on the skill component (e.g., tennis players, biathlon shooting) would likely not benefit from caffeine-induced jitters and arousal. However, athletes in sports that depend more on physical capabilities, such as strength and endurance (e.g., football lineman), might actually benefit from increased jitters and arousal before games. These aspects are less explored in research but certainly warrant consideration in the practical context to optimize the response to caffeine supplementation. The primary determinant in the incidence and severity of side-effects associated with caffeine ingestion is the dose used. Side-effects with caffeine seem to increase linearly with the dose ingested [ 239]. Therefore, they can be minimized-but likely not fully eliminated-by using smaller doses, as such doses are also found to be ergogenic and produce substantially fewer side-effects [ 112]. In summary, an individual case-by-case basis approach is warranted when it comes to caffeine supplementation, as its potential to enhance performance (benefit) needs to be balanced with the side-effects (risk).

Caffeine and cognitive performance

In addition to exercise performance, caffeine has also been studied for its contribution to athletes of all types (including Special Forces operators in the military) who are routinely required to undergo periods of sustained cognitive function and vigilance due to their job requirements (Table 1). A 2016 review [ 344] concluded that caffeine in doses from 32 to 300 mg (for a 75 kg individual) enhanced specific aspects of cognitive performance, such as attention, vigilance, and reaction time. Spriet [ 112] also concluded that lower doses of caffeine (approximately 200 mg) improved cognitive processes associated with exercise including vigilance, alertness, and mood. Hogervorst et al. [ 82] studied 24 well-trained cyclists that were randomized to 3 groups: (1) consumed a bar containing 45 g of carbohydrate and 100 mg of caffeine; (2) an isocaloric non-caffeine performance bar; or, (3) a placebo beverage (non-caloric flavored water) immediately before performing a 2.5-h ride followed by a time to exhaustion trial. They found that caffeine in a carbohydrate-containing performance bar significantly improved both endurance performance and complex cognitive ability during and after exercise [ 82]. Antonio et al. [ 345] assessed the effects of an energy drink on psychomotor vigilance in a small cohort of 20 exercise-trained men and women. The acute consumption of 300 mg of caffeine in a commercially available energy drink produced a significant improvement in psychomotor vigilance mean reaction time in these subjects compared to the placebo trial. This matches a 2001 IOM report [ 346] that the effects of caffeine supplementation include increased attention and vigilance, complex reaction time, and problem-solving and reasoning.

One confounding factor on cognitive effects of caffeine is the role of sleep. Special Forces military athletes conduct operations where sleep deprivation is common. A series of different experiments [ 42, 329, 330, 332, 334, 335, 346, 347] have examined the effects of caffeine in real-life military conditions. In three of the studies [ 329, 330, 334], soldiers performed a series of tasks such as a 4 or 6.3 km run and a marksmanship test, which is a task that requires fine motor coordination and steadiness, observation/reconnaissance, and requires long periods of no movement coupled with alertness and psychomotor vigilance over several days, where opportunities for sleep became more infrequent. Caffeine was provided at doses ranging from 600 to 800 mg in the form of chewing gum, owing to its practicality, i.e., rapid absorption and portability [ 58]. The investigators found that vigilance was either maintained or enhanced under the caffeine conditions (vs. placebo), in addition to improvements in run times and obstacle course completion [ 329, 330, 334]. Similarly, Lieberman et al. [ 42] examined the effects of caffeine on cognitive performance during sleep deprivation in U. S. Navy Seals. During this investigation, there were multiple doses of caffeine ingested, 100 mg, 200 mg, or 300 mg, in capsule form. Once again, results were also significant for the assessments related to vigilance and reaction time in both the 200 and 300 mg caffeine intervention, suggesting smaller successive doses of caffeine are more beneficial than large boluses, for improving focus and vigilance.

The positive effects of caffeine on cognitive function were further supported by work from Kamimori et al. [ 332] where 20 special forces operators were randomly assigned to receive four 200-mg doses of caffeine or placebo during a period of low sleep over three successive days. The caffeine intervention maintained psychomotor speed, improved event detection, increased the number of correct responses to stimuli, and increased response speed during logical reasoning tests. Under similar conditions of sleep deprivation, Tikuisis et al. [ 335] demonstrated that the cognitive component of a shooting task (i.e., target detection) benefited from caffeine. These studies [ 42, 329, 330, 332, 334, 335, 346, 347] demonstrate the effects of caffeine on vigilance and reaction time in a sleep deprived state, in a distinct and highly trained population, usually with repeated 'lower' doses, ~ 200 mg of caffeine ingestion. When subjects are not sleep deprived, the effects of caffeine on cognition appear to be less effective. For example, Share et al. [ 336] did not show any difference in shooting accuracy, reaction time, or target tracking times among the three intervention trials using 2 escalating doses of caffeine at 2 mg/kg and 4 mg/kg.

In addition to the ability of caffeine to counteract the stress from sleep deprivation, it may also play a role in combatting other stressors. Gillingham et al. [ 339] showed that in 12 reservists who ingested 5 mg/kg body mass of caffeine or placebo 1 h pre- and post-strenuous exercise, that caffeine ingestion mediated stress from sleep deprivation cited above. However, these benefits were not observed during more complex operations [ 339]. With a different stressor (a simulated firefight), no cognitive effect was seen with a caffeine dose of 400 mg [ 340]. Crowe et al. [ 341] examined the effects of caffeine (6 mg/kg dose) on cognitive parameters (visual reaction time and number recall tests) via two maximal 60-s bouts of cycling over three conditions (caffeine, placebo, control). Again, no cognitive benefit was observed.

Other studies [ 244, 338, 342, 343] support the effects of caffeine on the cognitive aspects of sport performance, even though with some mixed results [ 348, 349]. Foskett et al. [ 244] determined that a moderate dose (6 mg/kg) of caffeine enhanced the fine motor skills in soccer players as measured by improved ball passing accuracy and control. This was supported by Stuart et al. [ 342] who examined the effects of the same dose of caffeine (6 mg/kg) and found a 10% improvement in ball-passing accuracy. Equivocal results were reported for distance covered, agility, and accuracy in a review of 19 studies where caffeine ingestion before exercise was between 3 and 6 mg/kg [ 348]. Data on reactive agility time is split, with one study demonstrating a benefit [ 343] and another one [ 349] did not showing any benefit, despite using the same dose of caffeine (6 mg/kg). Finally, caffeine (5 mg/kg) was shown to enhance cognitive performance after an upper-body Wingate test, which may be beneficial in sports or occupational activities where there is a need for anaerobic performance concurrent with decision making (e.g. firefighting, military related tasks, wheelchair basketball) [ 338].

The exact mechanism of how caffeine enhances cognition in relation to exercise is not fully elucidated and appears to work through both peripheral and central neural effects [ 350]. In a study by Lieberman et al. [ 42], 8 h after caffeine administration, caffeine continued to enhance motor learning and short-term memory via performance of repeated acquisition. Repeated acquisition are behavioral tests in which subjects are required to learn new response sequences within each experimental session [ 351]. The researchers [ 42] speculated that caffeine exerted its effects from an increased ability to sustain concentration, as opposed to an actual effect on working memory. Other data [ 352] were in agreement that caffeine reduced reaction times via an effect on perceptual-attentional processes (not motor processes). This is in direct contrast to earlier work that cited primarily a motor effect [ 353]. Another study with a sugar free energy drink showed similar improvements in reaction time in the caffeinated arm; however, they attributed it to parallel changes in cortical excitability at rest, prior, and after a non-fatiguing muscle contraction [ 354]. The exact cognitive mechanism(s) of caffeine have yet to be elucidated.

Based on some of the research cited above, it appears that caffeine is an effective ergogenic aid for individuals either involved in special force military units or who may routinely undergo stress including, but not limited to, extended periods of sleep deprivation. Caffeine in these conditions has been shown to enhance cognitive parameters of concentration and alertness. It has been shown that caffeine may also benefit sport performance via enhanced passing accuracy and agility. However, not all of the research is in agreement. It is unlikely that caffeine would be more effective than actually sleeping, i.e. you cannot 'outcaffeinate' poor sleep.

Environmental influences on response to caffeine

Physical activity and exercise in extreme environments are of great interest as major sporting events (e.g. Tour de France, Leadville 100, Badwater Ultramarathon) are commonly held in extreme environmental conditions. Events that take place in the heat or at high altitudes bring additional physiological challenges (i.e., cardiovascular strain, thermoregulation, diuresis) for athletes, which may be potentially compounded if caffeine is consumed prior to and/or during training or competition in such environments [ 355]. Nonetheless, caffeine is widely used by athletes as an ergogenic aid when exercising or performing in extreme environmental situations. The current understanding of caffeine's impact on exercise performance is based largely on the findings of analyses conducted in controlled, temperate environments, whereas data collected on the ergogenic effect of caffeine consumption by individuals performing in the heat or at altitude are limited and have resulted in inconsistent findings.

Alternate caffeine sources

Sources other than commonly consumed coffee and caffeine tablets have garnered interest, including caffeinated chewing gum, mouth rinses, aerosols, inspired powders, energy bars, energy gels and chews, among others. While the pharmacokinetics [ 18, 373- 376] and effects of caffeine on performance when consumed in a traditional manner, such as coffee [ 47, 49, 55, 153, 368, 377, 378] or as a caffeine capsule with fluid [ 55, 203, 379, 380] are well understood, curiosity in alternate forms of delivery (as outlined in pharmacokinetics section) have emerged due to interest in the speed of delivery [ 81]. A recent review by Wickham and Spriet [ 5] provides an overview of the literature pertaining to caffeine use in exercise, in alternate forms. Therefore, here we only briefly summarize the current research.

Caffeine in combination with other ingredients

Summary

Caffeine in its many forms is a ubiquitous substance frequently used in military, athletic and fitness populations which acutely enhance many aspects of exercise performance in most, but not all studies.

Supplementation with caffeine has been shown to acutely enhance many aspects of exercise, including prolonged aerobic-type activities and brief duration, high-intensity exercise. Caffeine is ergogenic when consumed in doses of 3-6 mg/kg body mass. The most commonly used timing of caffeine supplementation is 60 min pre-exercise. The optimal timing of caffeine ingestion likely depends on the source of caffeine. Caffeine's effects seem to be similar in both trained and untrained individuals. Studies that present individual participant data commonly report substantial variation in caffeine ingestion responses. Inter-individual differences may be associated with habitual caffeine intake, genetic variations, and supplementation protocols in a given study. Caffeine may be ergogenic for cognitive function, including attention and vigilance. Caffeine may improve cognitive and physical performance in some individuals under conditions of sleep deprivation. Caffeine at the recommended doses does not appear significantly influence hydration, and the use of caffeine in conjunction with exercise in the heat and at altitude is also well supported. Alternative sources of caffeine, such as caffeinated chewing gum, mouth rinses, and energy gels, have also been shown to improve performance. Energy drinks and pre-workouts containing caffeine have been demonstrated to enhance both anaerobic and aerobic performance. Individuals should also be aware of the side-effects associated with caffeine ingestion, such as sleep disturbance and anxiety, which are often linearly dose-dependent.

Authors' contributions

N.S.G conceived and outlined the sections to be included in the manuscript, provided the initial draft and oversaw all critical edits and revisions. T.A.V authored multiple sections and participated in final editing and revisions. M.T.N, J. G and B.J.S provided expertise and contributed to the one or more sections of the manuscript. N.D.M.J, S.M.A, J. A, J.R.S, E.T.T, A.E.S-R, E.R.G, and D.S.K provided valuable comments and suggested minor edits to the manuscript. B.I.C. oversaw the writing process, and all authors reviewed and gave final approval of the version to be published.

Funding

No funding was received for the research, writing or publication of this manuscript.

Availability of data and materials

Not applicable.

Ethics approval and consent to participate

This paper was reviewed by the International Society of Sports Nutrition Research Committee and represents the official position of the Society.

Consent for publication

Not applicable.

Competing interests

N.S.G consults for and is on the scientific advisory board of Nutrigenomix, a genetic testing company. T.A.V is on the scientific advisory board for Dymatize Nutrition, a manufacturer of sports supplements; has received research grants related to dietary supplements. B.J.S is on the scientific advisory board for Dymatize Nutrition, a manufacturer of sports supplements. S.M.A has received grants to evaluate the effects of dietary supplements, including caffeine and caffeine-derivatives, serves or has served on scientific advisory boards for sport nutrition companies, has been a paid consultant for a coffee company, and holds patents for an ingredient used in a performance coffee product. J. A is the CEO of the ISSN. The ISSN has received grants from sports supplement companies that sell caffeine-based products. E.T.T earns income as a writer and practitioner within the fitness industry. A.E.S-R has received research grants related to dietary supplements and is a science advisor to Ladder Sport. D.S.K declares that in part, he works for a contract research company that conducts research and human clinical trials for industries including dietary supplements, medical foods, beverages, foods, pharmaceuticals and medical devices. He also sits on the Scientific Advisory Board for Dymatize Nutrition (BellRing Brands) B.I.C is on the scientific advisory board for Dymatize Nutrition, a manufacturer of sports supplements. M.T.N, J. G, N.D.M.J, J.R.S, E.R.G, report no competing interests or conflicts of interest.

References

204. Olympic.org. Rio 2016 Cycling Road 2016.

316. Brooks JHWK, Chrismas BCR. Acute effects of caffeine on strength performance in trained and untrained individuals. J Athl Enhanc. 2015;4.

Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

Not applicable.

Articles from Journal of the International Society of Sports Nutrition are provided here courtesy of Taylor & Francis

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International society of sports nutrition position stand: caffeine and exercise performance

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Following critical evaluation of the available literature to date, The International Society of Sports Nutrition (ISSN) position regarding caffeine intake is as follows: Supplementation with caffeine has been shown to acutely enhance various aspects ...

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Nutrient Timing: Fueling Strategies to Unlock Peak Performance

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Nutrient Timing: Fueling Strategies to Unlock Peak Performance

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Ryan O'Born

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As an athlete, you’re likely bombarded by advice from coaches, trainers at the gym, and teammates and friends about what you should be eating, how much, and when. You probably even get advice from people on social media who have never even met you! Whether you’re an endurance runner, a team sport competitor, or a strength and power athlete, Nutrient Timing: Fueling Strategies to Unlock Peak Performance gives you science-backed advice that has been translated into practical recommendations to help optimize your training, boost performance, and accelerate recovery. Learn why nutrient timing matters and how to identify your specific timing needs. Find carb, protein, fat, fluid, and supplement recommendations--for before, during, and after training or competition--that are specific to your situation, activity level, and sport. Use the sample nutrition plans and case studies for various sports and situations to help facilitate the implementation of those recommendations. Get time-saving food prep and meal planning tips to help keep your unique nutrition plan on track. And if your goal is to gain muscle, lose fat, or recover from an injury, that’s covered as well. If you want to train hard, perform to the best of your ability, recover quickly, and maintain a competitive edge over your opponent, let Nutrient Timing be your guide. It will give you insight into the ideal types of nutrients to consume, their quantities, and their timing to enhance your performance and achieve your goals. Earn continuing education credits/units! A continuing education exam that uses this book is also available. It may be purchased separately or as part of a package that includes both the book and exam.

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Lunch Tips for Athletes: What to eat and How Much

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Elizabeth Cain

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How Sports Health Professional Perceive and Prescribe Nutritional Supplements to Olympic and Non-Olympic Athletes

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How Sports Health Professional Perceive and Prescribe Nutritional Supplements to Olympic and Non-Olympic Athletes

# data[].attributes.body
Amanda Noel

# data[].attributes.attachment_link.title
How Sports Health Professionals Perceive and Prescribe Nutritional Supplements to Olympic and Non-Olympic Athletes

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Background: A wide range of sports health professionals provide nutritional supplement advice. We aimed to better understand the expertise, knowledge, and attitudes of sports health professionals toward nutritional supplements and third-party supplement testing. Methods: A web-based questionnaire was used to ask questions about nutritional supplement knowledge and attitudes toward the Dutch third-party supplement testing system (NZVT), about supplement efficacy, and if professionals advise these supplements, as well as which profession can be deemed the expert on nutritional supplements. Results: A total of n = 320 sports health professionals delivered input, of which 45% worked with Olympic athletes and 18% were sports dietitians. Sports dietitians were ranked as the most knowledgeable professionals about sports nutrition (80%) and nutritional supplements (74%), and a literature-based comparison showed the most favorable knowledge, attitudes, and ergogenic classifications of supplement scores for sports dietitians compared with other sports health professions. Sports health professionals working with Olympic athletes scored similar but slightly lower trends on self-reported knowledge, attitude and third-party supplement testing than sports dietitians but substantially better than professionals not working with Olympic athletes. Conclusion: Sports dietitians are seen as the absolute expert on supplements by other sports health professionals, with professionals working with Olympic athletes reporting similar trends, and other sports health professionals do have lower self-reported knowledge and preferred attitudes toward effective and safe use of dietary supplements.

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Timing, optimal dose and intake duration of dietary supplements with evidence-based use in sports nutrition

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Taylor Reed

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Timing, optimal dose and intake duration of dietary supplements with evidence-based use in sports nutrition

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Emma Piercy

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Food energy

The energy needs of athletes exceed those of the average person. It's not uncommon for male and female athletes, especially those still growing, to have caloric needs exceeding 2,400-3,000 kcal and 2,200-2,700 kcal per day, respectively. The amount of energy found within a given food is dependent on the macronutrient (carbohydrate, protein and fat) content of the item.
Macro-nutrient > Energy content
*Although alcohol is not considered a macronutrient, it's important for athletes to realize that it is higher in calories and can contribute to undesirable weight gain.

Carbohydrates serve as the primary source of energy during activities of higher intensity. Healthy carbohydrate food sources include fruits, vegetables, whole-grain cereals, breads and pastas.

Dietary fat also plays a key role in helping individuals meet their energy needs as well as supporting healthy hormone levels. Healthy sources of fat include nuts, nut butters, avocados, olive and coconut oils. Limit use of vegetable oils such as corn, cottonseed or soybean oil.

Dietary protein plays a key role in muscle repair and growth. Preferred sources of protein include lean meats, eggs, dairy (yogurt, milk, cottage cheese) and legumes.

Tips to excel with proper sports nutrition

1. Make a plan to eat a variety of fruits and vegetables daily. The goal is to eat at least five servings per day, and include varieties of fruit and vegetable color. One serving is approximately the size of a baseball. Fruits and vegetables are filled with the energy and nutrients necessary for training and recovery. Plus, these antioxidant-rich foods will help you combat illness like a cold or the flu.

2. Choose whole grain carbohydrates sources such as whole-wheat bread or pasta, and fiber-rich cereals as power-packed energy sources. Limit the refined grains and sugars such as sugary cereals, white breads and bagels. You'll benefit more from whole-grain products.
Choose healthy sources of protein such as chicken, turkey, fish, peanut butter, eggs, nuts and legumes.

3. Stay hydrated with beverages, as a two percent drop in hydration levels can negatively impact performance. Options include milk, water, 100 percent fruit juice and sport drinks. However, realize that sport drinks and 100 percent fruit juice tend to be higher in overall sugar content and, in the case of fruit juice, lack many of the health benefits present in its whole food counterpart. Also, be sure not to confuse sports drinks such as Gatorade with "energy" drinks such as Red Bull and similar beverages.

4. Stick with whole food options as much as possible as opposed to highly processed foods.

Planning a nutritious meal

Without adequate calories from the healthiest food sources, you will struggle to achieve your performance goals. Plan a nutritious meal by choosing at least one food from each category.

Carbohydrates
Protein Healthy fat
Hydration

Adequate hydration is a key element in sports performance. Most athletes benefit from developing a personal hydration plan. A general rule for training is to consume a minimum:

Two cups of fluid prior to training

Four to six ounces of fluid every 15 minutes of exercise

Your post event/training hydration needs are impacted by your overall pre- to post-fluid losses. To properly assess, weigh yourself immediately prior to and after a workout. For every pound of weight lost, replace with 16 ounces of fluid. Best hydration choices include water, low-fat milk or 100 percent juice. Sports beverages are best reserved for competition, where quick hydration and electrolyte replacement are necessary.

Game day nutrition

There are a few golden rules when it comes to eating on game day:

Remember, proper nutrition for the "big tournament/race/meet" does not happen on the day of the event alone. It happens the days, weeks, and months leading up to the competition

Never experiment with a new dietary/supplement protocol on game day. First, try it out prior to a practice/training session to make sure you tolerate it well.

As you get closer to the game/competition, make your meals smaller. Additionally, you may want to limit dairy, fat and fibrous carbohydrate sources during the last one to one and one-half hours pre-event/practice, as these may cause GI issues.

On-the-go Eating

Peak performance during competition means eating nutritious food while traveling. Relying on the concession stand for food during competition is an almost certain failure. Players (and parents) should prepare by packing a variety of food and beverages.

Choose energy-packed foods such as whole grain crackers with low-fat cheese, tortilla wraps with veggies and lean meat, hard-boiled eggs, vegetable or bean soups, small boxes of non-sugary cereal, fresh fruit, mini-whole wheat bagels with peanut butter, pita bread with hummus or pasta with grilled chicken. Pair any of these options with fruit/vegetable and milk and you've got a great meal.

Healthy food choices > Not-so-healthy food choices

Grilled chicken, turkey or fish > Fried chicken or fish

Lean beef or pork > Burgers, sausage, bacon

Fruits, vegetables, salads, veggie-based soups > French fries, fried rice, alfredo or cheese sauce

Nuts, trail mix, seeds or peanut butter > Chips, cheese curls, pork rinds

Eggs or egg substitutes > Omelets loaded with cheese, hash browns and sausage

Who grain breads, rice and pasta > Highly-processed white bread, rice and pasta

Dairy products > Dairy products with excessive added sugars, like ice cream

As you get closer to the game/competition, make your meals smaller, removing fats and dairy products. Fibrous carbohydrates can be beneficial as these tend to cause GI disturbances.

The key thing with "pre-event" nutrition is making sure that you've tested it out before game day. Try the pre-meal/snack protocol in advance to make sure you tolerate it well.

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Eggs, Salmon, Milk, Banana, Avocado

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Salmon, Chicken, Pork

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Creatine: Uses, Side Effects, Interactions, Dosage, and Warning

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Find patient medical information for Creatine on WebMD including its uses, effectiveness, side effects and safety, interactions, dosage, user ratings and products that have it

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Corey FW

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B vitamins are water-soluble vitamins that are important for various bodily processes. They are found in many unprocessed foods, and can also be taken as a dietary supplement.

Every day, your body needs to get the right amount of vitamins and nutrients to keep it healthy and working well. Of the 13 vitamins that your body needs, 8 of them are B vitamins. They are:

The many benefits of B vitamins come from their ability to help your body turn energy-yielding nutrients - such as carbohydrates - into fuel. Without them your body would not have enough energy.

Because your body can't store all of the B-group vitamins, it's important that you continuously get them through your diet. Here are five foods that are high in B vitamins:
1. Whole Grains
Because food processing removes nutrients from grains, you want to eat whole grains that have not undergone this process. Grains high in B vitamins include:
2. Eggs
Eggs are a good source of B vitamins, especially pantothenic acid (B5) and Cyanocobalamin (B12).

Two large eggs provide 46% of your daily value of vitamin B12 and 39% of your daily value of vitamin B2.
3. Legumes
Legumes are a food group that includes beans, lentils, and garbanzo beans. In addition to being a rich source of B vitamins, legumes can also help lower your blood sugar and cholesterol.

4. Citrus Fruits
Citrus fruits - such as oranges, clementines, and lemons - check off at least six of the eight B vitamins. They contain:

Thiamin (B1)

Riboflavin (B2)

Niacin (B3)

Pantothenic acid (B5)

Pyridoxine (B6)

Folate or "folic acid" (B9)

5. Avocados
Avocados contain almost 20 vitamins and minerals. Just 1 cup of avocados (150 grams) contains 30% of your daily folate requirement and 23% of vitamin B6. Other health benefits of avocados include:
6.Meat, Poultry, Fish
Meat (pork, beef, etc.), poultry (chicken, turkey, etc.), and fish (tuna, salmon, etc.) are excellent sources of vitamin B3, vitamin B6, and vitamin B12. They also contain other important minerals such as potassium, chromium, iron, selenium, and zinc.
7. Fortified Breakfast Cereals
Many types of breakfast cereals are fortified with various B vitamins, including thiamin (vitamin B1), riboflavin (vitamin B2), vitamin B6, folate, and vitamin B12.
8. Liver
Animal liver is an excellent source of thiamin (vitamin B1) and folate. Eating liver can also provide vitamin A, riboflavin, copper, iron, and choline.

The B vitamin group plays a special role in your body. First of all, B vitamins help enzymes (which break down what you eat and drink) with several functions, including:

Releasing energy from proteins, carbohydrates, and fats

Breaking down amino acids

Moving oxygen and energy around your body

B vitamins also help your cells grow and multiply. Some B vitamins also aid the body's production of hemoglobin, which is important for red blood cells. Hemoglobin gives blood its red color and also helps transport oxygen throughout your body.

Some other health benefits of B vitamins include:
Immune Function
Vitamin B6, or pyridoxine, supports biochemical reactions in your immune system. Taking this B vitamin as a supplement has been proven to increase immune responses in people who are critically ill.
Brain Health
Data from studies suggests that the more B vitamins there are in your blood, the better your performance will be with tests involving memory, problem-solving, and word and sentence formation.
Disease Prevention
Vitamin B6 and B12 appear to play roles in reducing heart disease and some types of cancer. However, there is also research to suggest that long-term use of these two B vitamins might increase lung cancer risk in men.

Although B vitamins are naturally found in many foods, they are easily destroyed by alcohol and cooking. Food processing also strips foods of their B vitamin content, especially in white flour, white bread, and white rice.

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B Vitamins are a collection of 8 water-soluble vitamins important for various bodily processes. Learn which 5 foods to eat to get more B vitamins.

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The list below provides information gathered from press releases and other public notices about certain recalls of FDA-regulated products. Not all recalls have press releases or are posted on this page. See Additional information about recalls for a more complete listing.

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Recalls, Market Withdrawals, & Safety Alerts

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FDA and industry press releases regarding product recalls

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You can get enough vitamin C by eating a variety of foods including citrus fruits (such as oranges and grapefruit) and their juices, as well as red and green pepper, kiwifruit, broccoli, strawberries, baked potatoes, and tomatoes.

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Vitamin and Mineral Supplement Fact Sheets

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You can get enough vitamin C by eating a variety of foods including citrus fruits (such as oranges and grapefruit) and their juices, as well as red and green pepper, kiwifruit, broccoli, strawberries, baked potatoes, and tomatoes.

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How to report a problem with a dietary supplement

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How to report a problem with a dietary supplement

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Dietary supplements include vitamins, minerals, herbs, amino acids, whey protein, and creatine. FDA does not approve dietary supplements before they are sold to the public. Therefore, it is particularly important for consumers, healthcare professionals, and industry members to report health-related reactions or illnesses (also known as adverse events) to FDA, so we can evaluate the marketplace and take action to protect the public from possibly unsafe products.
Serious reactions or illnesses may include:

Itching, rash, hives, throat/lip/tongue swelling, or wheezing

Low blood pressure, fainting, chest pain, shortness of breath, palpitations, or irregular heartbeat

Severe, persistent nausea, vomiting, diarrhea, or abdominal pain

Difficulty urinating, decreased urination, or dark urine

Blood in urine, stool, vomit, or sputum

Abnormal bleeding from nose or gums

Fatigue or appetite loss

Yellowing of the skin or eyes

Severe joint or muscle pain

Marked mood (irritability, anxiety), cognitive, or behavioral changes, thoughts of suicide

Stroke (slurred speech, one-sided weakness of face, arm, leg, or blurry/loss of vision)

Adverse reactions can even result in Emergency Room visits or hospitalization.

For Consumers and Healthcare Professionals

If you think that a dietary supplement may have caused you or someone you know to have a serious reaction or illness, immediately stop using the product and fill out a safety report through the Safety Reporting Portal to submit your complaint to FDA.

After logging in or choosing to report as a guest, select the option "Start a new report" and choose "A private citizen, business or veterinary provider submitting a voluntary report." Please supply as much information as you can. Complete reports are the most helpful, but even pieces of information can help FDA identify potentially dangerous products.

For Industry

Members of the dietary supplement industry may now use the reporting form on the Safety Reporting Portal to meet the reporting requirements established in section 761 of the Federal Food, Drug, and & Cosmetic Act.

After logging in or choosing to report as a guest, select the option "Start a new report" and choose "A manufacturer, packer or distributor of a human dietary supplement."

If You Need Assistance

If you have any questions about reporting on dietary supplements, please contact DSRSupport@fda.hhs.gov. For technical support with submitting a safety report, please contact SRPSupport@fda.hhs.gov.

For information on how to report a problem with food, visit How to Report a Problem with Food.

For information on health fraud and how to report fraudulent products, visit Health Fraud Scams.

To report problematic advertising for a dietary supplement, contact the Federal Trade Commission (FTC).

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How to Report a Problem with Dietary Supplements

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How to report a serious reaction or illness associated with a dietary supplement.

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Hayley Quinn

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What is creatine?

Creatine is a natural source of energy that helps your skeletal muscles flex (contract). It helps create a steady supply of energy in your muscles so they can keep working, especially while you're exercising.

About half of your body's supply of creatine (1 to 2 grams/day, about the size of 1 to 2 jellybeans) comes from your diet, especially protein-rich foods such as:

Red meat (pork, veal and beef).

Seafood (fish and shellfish).

Animal milk (like cow, goat and sheep milk).

Your body produces the other half naturally in your liver, kidneys and pancreas. They deliver about 95% of the creatine to your skeletal muscles to use during physical activity. The rest goes to your heart, brain and other tissues.

Manufacturers also make creatine supplements. Some people take creatine supplements because they work out a lot or don't get enough creatine in their diet. Creatine supplements exist as:

Is it healthy to take creatine?

Studies show that it's safe for many people to take creatine supplements. However, there isn't enough evidence to know if it's safe if you:

Are pregnant or breastfeeding (chestfeeding).

Have diabetes.

Have kidney disease.

Have liver disease.

If you have bipolar disorder, creatine may also increase your risk of mania.

Talk to a healthcare provider before taking creatine to ensure it's safe for you.

Does creatine make you gain muscle?

It depends. Studies show that regularly taking creatine, weightlifting and exercising can help increase muscle growth in people 18 to 30 years old. However, there isn't enough research to say that creatine helps develop muscle growth in people older than 65 or people with diseases that affect their muscles.

Why do people take creatine supplements?

Many amateur and professional athletes take creatine supplements to aid their workout routines and improve their recovery. Creatine creates "quick burst" energy and increased strength, which improves your performance without affecting your ability to exercise for longer periods (aerobic endurance).

Most athletes who take creatine supplements participate in power sports, including:

In addition, studies suggest that creatine supplements may help brain function in people 60 and older. This includes:

Short-term memory.

Reasoning.

Neuroprotection (keeping groups of nerve cells safe from injury or damage).

Researchers are still studying whether creatine supplements may help people with cognitive (mental) conditions, including dementia.

Talk to a healthcare provider before taking creatine supplements, regardless of your level of physical fitness, age or health.

Are creatine supplements recommended for athletes?

Many athletes use creatine supplements. Professional sports organizations, the International Olympic Committee (IOC) and the National Collegiate Athletic Association (NCAA) all allow athletes to use creatine supplements.

Men and women and people assigned male or female at birth ( AMAB or AFAB) report benefits to using creatine. But some studies note that women and people AFAB who take creatine supplements may not gain as much strength or muscle mass as men and people AMAB.

What is the most common type of creatine supplement?

The most common creatine supplement is creatine monohydrate. It's a dietary supplement that increases muscle performance in short-duration, high-intensity resistance exercises, such as weightlifting, sprinting and bicycling. Other forms of creatine don't appear to have these benefits.

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Creatine is one of your body's natural energy sources for muscle contraction. Many athletes take creatine supplements to increase strength and improve recovery.

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Hayley Quinn

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You're probably familiar with Vitamin B6 and B12, but did you know there are actually eight B vitamins?

These vitamins help a variety of enzymes do their jobs, ranging from releasing energy from carbohydrates and fat to breaking down amino acids and transporting oxygen and energy-containing nutrients around the body.

Spotlight on Three of the Bs: Folate, Vitamin B6, and Vitamin B12

One of the advances that changed the way we look at vitamins was the discovery that too little folate is linked to birth defects such as spina bifida and anencephaly.

Folate (Folic Acid) - Vitamin B9

Folate is the natural form of vitamin B9, water-soluble and naturally found in many foods. It is also added to foods and sold as a supplement in the form of folic acid; this form is actually better absorbed than that from food sources-85% vs. 50%, respectively.
Learn more about folate and health
Another line of research about folate and two other B vitamins, vitamin B6 and vitamin B12, explores their roles in reducing some types of cancer and heart disease.

Vitamin B12

Vitamin B12, or cobalamin, is naturally found in animal foods. It can also be added to foods or supplements. Vitamin B12 is needed to form red blood cells and DNA. It is also a key player in the function and development of brain and nerve cells.
Learn more about vitamin B12 and health
Related
Vitamins and Minerals Last reviewed March 2023
Terms of Use

The contents of this website are for educational purposes and are not intended to offer personal medical advice. You should seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website. The Nutrition Source does not recommend or endorse any products.

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You're probably familiar with Vitamin B6 and B12, but did you know there are actually eight B vitamins? B1 (thiamin) B2 (riboflavin) B3 (niacin) B5 (pantothenic acid) B6 (pyridoxine) B7 (biot...

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James Nash

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What is creatine?

Creatine is a natural source of energy that helps your skeletal muscles flex (contract). It helps create a steady supply of energy in your muscles so they can keep working, especially while you're exercising.

About half of your body's supply of creatine (1 to 2 grams/day, about the size of 1 to 2 jellybeans) comes from your diet, especially protein-rich foods such as:

Red meat (pork, veal and beef).

Seafood (fish and shellfish).

Animal milk (like cow, goat and sheep milk).

Your body produces the other half naturally in your liver, kidneys and pancreas. They deliver about 95% of the creatine to your skeletal muscles to use during physical activity. The rest goes to your heart, brain and other tissues.

Manufacturers also make creatine supplements. Some people take creatine supplements because they work out a lot or don't get enough creatine in their diet. Creatine supplements exist as:

Is it healthy to take creatine?

Studies show that it's safe for many people to take creatine supplements. However, there isn't enough evidence to know if it's safe if you:

Are pregnant or breastfeeding (chestfeeding).

Have diabetes.

Have kidney disease.

Have liver disease.

If you have bipolar disorder, creatine may also increase your risk of mania.

Talk to a healthcare provider before taking creatine to ensure it's safe for you.

Does creatine make you gain muscle?

It depends. Studies show that regularly taking creatine, weightlifting and exercising can help increase muscle growth in people 18 to 30 years old. However, there isn't enough research to say that creatine helps develop muscle growth in people older than 65 or people with diseases that affect their muscles.

Why do people take creatine supplements?

Many amateur and professional athletes take creatine supplements to aid their workout routines and improve their recovery. Creatine creates "quick burst" energy and increased strength, which improves your performance without affecting your ability to exercise for longer periods (aerobic endurance).

Most athletes who take creatine supplements participate in power sports, including:

In addition, studies suggest that creatine supplements may help brain function in people 60 and older. This includes:

Short-term memory.

Reasoning.

Neuroprotection (keeping groups of nerve cells safe from injury or damage).

Researchers are still studying whether creatine supplements may help people with cognitive (mental) conditions, including dementia.

Talk to a healthcare provider before taking creatine supplements, regardless of your level of physical fitness, age or health.

Are creatine supplements recommended for athletes?

Many athletes use creatine supplements. Professional sports organizations, the International Olympic Committee (IOC) and the National Collegiate Athletic Association (NCAA) all allow athletes to use creatine supplements.

Men and women and people assigned male or female at birth ( AMAB or AFAB) report benefits to using creatine. But some studies note that women and people AFAB who take creatine supplements may not gain as much strength or muscle mass as men and people AMAB.

What is the most common type of creatine supplement?

The most common creatine supplement is creatine monohydrate. It's a dietary supplement that increases muscle performance in short-duration, high-intensity resistance exercises, such as weightlifting, sprinting and bicycling. Other forms of creatine don't appear to have these benefits.

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Creatine is one of your body's natural energy sources for muscle contraction. Many athletes take creatine supplements to increase strength and improve recovery.

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James Nash

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About B-group vitamins

naturally occur in food and are needed in very small amounts for various bodily functions such as energy production and making red blood cells. There are 13 vitamins that our body needs, 8 of which make up the B-group (or B-complex) vitamins.

The B-group vitamins do not provide the body with fuel for energy, even though supplement advertisements often claim they do. However, it's true though that without B-group vitamins the body lacks energy. This is because the B-group vitamins are needed to help the body to use the energy-yielding nutrients (such as , and ) for fuel. Other B-group vitamins are needed to help cells to multiply by making new DNA.

Vitamin B in food

Even though the B-group vitamins are found in many foods, they are water soluble and are generally quite delicate. They are easily destroyed, particularly by and cooking.

can also reduce the amount of B-group vitamins in foods - either by destroying them, or in white flours, white breads and white rice removing the parts that contain the most B-group vitamins. This is one of the reasons white flours, white breads and white rice are less nutritious than their wholegrain counterparts.

The body has a limited capacity to store most of the B-group vitamins (except B12 and folate, which are stored in the liver). A person who has a poor diet for a few months may end up with B-group vitamins deficiency. For this reason, it's important that adequate amounts of these vitamins be eaten regularly as part of a well-balanced, nutritious diet.

Vitamin B supplements

Taking vitamins that your body does not need can mean, at a best-case scenario, that your body gets rid of the excess in your urine (so you waste your money). But some vitamins can also be toxic if taken incorrectly, so you could also be damaging your body instead of helping it.

Some B-group vitamins also work together in the body (for example, vitamin B12 and folate or folic acid). This means taking supplements can sometimes hide deficiencies of other vitamins, which can also lead to health problems.

Types of vitamin B

There are 8 types of vitamin B:

thiamin (B1)

riboflavin (B2)

niacin (B3)

pantothenic acid (B5)

pyridoxine (B6)

biotin (B7)

folate or 'folic acid' when included in supplements (B9)

cyanocobalamin (B12).

Thiamin (B1)

Thiamin is also known as vitamin B1. It helps to convert glucose into energy and has a role in nerve function.

Good sources of thiamin

In Australia, it's mandatory that white and wholemeal flour used for bread is .

Thiamin deficiency

Beriberi is a condition caused by thiamin deficiency and affects the cardiovascular, muscular, gastrointestinal and nervous systems. It can be classified as 'wet' and 'dry' beriberi. 'Dry' beriberi affects the nervous symptom while 'wet' beriberi affects the cardiovascular system.

Wernicke-Korsakoff syndrome (also called 'wet brain') is another thiamin-deficiency disease linked to alcohol excess and a thiamin-deficient diet. Alcohol reduces thiamin absorption in the gut and increases its excretion from the kidneys.

Riboflavin (B2)

Riboflavin is primarily involved in energy production and helps vision and skin health.

Good sources of riboflavin

yoghurt

cottage cheese

wholegrain breads and cereals

egg white

leafy green vegetables

yeast

liver

kidney.

Riboflavin deficiency (ariboflavinosis)

Riboflavin deficiency (or ariboflavinosis) is rare and is usually seen along with other B-group vitamin deficiencies. People at risk include those who consume excessive amounts of alcohol and those who do not consume milk or .

Niacin (B3)

Niacin is essential for the body to convert carbohydrates, fat and alcohol into energy. It helps maintain skin health and supports the nervous and digestive systems. Unlike other B-group vitamins, niacin is very heat stable and little is lost in cooking.

Good sources of niacin

Niacin deficiency (pellagra)

People who drink excessive amounts of alcohol or live on a diet almost exclusively based on corn are most at risk of pellagra. Others causes are associated with digestive problems where the body does not absorb niacin efficiently.

Excessive niacin intake

Large doses of niacin produce a drug-like effect on the nervous system and on blood fats. While favourable changes in blood fats are seen, side effects include flushing, itching, nausea and potential liver damage.

Pantothenic acid (B5)

Pantothenic acid is needed to metabolise carbohydrates, proteins, fats and alcohol as well as produce red blood cells and steroid hormones.

Good sources of pantothenic acid

Pantothenic acid is widespread and found in a range of foods, but some good sources include:

Pantothenic acid deficiency

Because pantothenic acid is found in such a wide variety of foods, deficiency is extremely rare.

Vitamin B6 (pyridoxine)

Pyridoxine is needed for protein and carbohydrate metabolism, the formation of red blood cells and certain brain chemicals. It influences brain processes and development, and steroid hormone activity.

Good sources of pyridoxine

Pyridoxine deficiency

Excessive pyridoxine intake

Pyridoxine toxicity is mostly due to supplementation and can lead to harmful levels in the body that can damage the nerves.

Biotin (B7)

Biotin (B7) is needed for energy , fat synthesis, amino acid metabolism and glycogen synthesis. High biotin intake can contribute to raised blood cholesterol levels.

Good sources of biotin

Biotin deficiency

Biotin deficiency is very rare - it's widely distributed in foods and only required in small amounts. Over-consumption of raw egg whites over periods of several months (by bodybuilders, for example) can induce deficiency because a protein in the egg white inhibits biotin absorption.

Folate or folic acid (B9)

Folate, or folic acid (the synthetic form of folate which is used extensively in dietary supplements and ) is needed to form red blood cells, which carry oxygen around the body. It helps the development of the , as well as DNA synthesis and cell growth. Women of child-bearing age need a diet rich in folate for this reason.

If , you should visit your doctor to make sure you're getting enough folate. This is important to reduce the risks of neural tube defects such as spina bifida in the baby.

Good sources of folate

Since 2009, all bread sold in Australia (except organic) has been fortified with folic acid.

Excessive folic acid intake

Although folic acid is generally considered non-toxic, excessive intakes above 1,000mcg per day over a period of time can lead to malaise, irritability and intestinal dysfunction. The main risk with excessive folate intake is that it can mask a vitamin B12 deficiency, so it's best to consume these 2 vitamins within the recommended amounts.

Cyanocobalamin (B12)

Cyanocobalamin (or vitamin B12) helps to produce and maintain the myelin surrounding nerve cells, mental ability, red blood cell formation and the breaking down of some fatty acids and amino acids to produce energy. Vitamin B12 has a close relationship with folate, as both depend on the other to work properly.

Good sources of B12

Vitamin B12 deficiency

Because vitamin B12 is only found in foods from animal sources, people following strict , as well as breastfed babies of vegan mothers, tend to be most commonly affected.

Absorption of B12 from the gut also tends to , so the elderly is another group who are more at risk of deficiency.

Where to get help

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The eight B-group vitamins are essential for various functions within the body.

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Dietary Sources of B Vitamins:
-bananas, milk, eggs, avocado, wholewheat bread
-NHS, Harvard, HealthDirect, Medline Plus

Dietary Sources of Creatine:
-red meat, seafood, animal milk
-Cleveland Clinic

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5 dietary sources of B vitamins:
1)salmon
2)eggs
3)milk
4)beef
5)yogurt
(Healthline Website)

3 sources of dietary creatine:
1)salmon
2)pork
3)chicken
(Medical News Today)

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5 dietary sources of B vitamins: Eggs, salmon, avocado, banana, leafy greens (NHS)

3 sources of dietary creatine: pork, salmon, chicken (NHS)

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Creatine

chemical structure of creatine

What is Creatine?

Creatine is an amino acid, with the chemical name methyl guanidine-acetic acid, that can be converted into the phosphocreatine. Phosphocreatine is storage mechanism muscle cells use to regenerate the cells primary source of energy adenosine triphosphate (ATP). Phosphocreatine has the ability to react with adenosine diphosphate (ADP), a byproduct of muscle contraction, and convert ADP to ATP for immediate energy.

Were does it come from?

Creatine can be synthesized in the liver, kidney, and pancreas from the three common amino acids Arginine, Glycine and Methionine. This involves a reversible transfer of an amidine group from arginine to glycine to form guanidinoacetic acid. An irreversible transfer of a methyl group then follows up this step from S-adenosylmethionine to the guanidinoacetic acid to form creatine. When creatine is obtained in the diet this mechanism is suppressed. Creatine can also be located in the diet from milk, steak and some fish. Beef, pork, tuna, salmon, and cod all contain between 1.4 to 2.3 grams of creatine per pound. Herring contains the most creatine at 3 to 4.5 grams per pound. Recently creatine supplementation has become an issue as a performance enhancing product.

How can Creatine be taken?

There are many products available for the supplementation of creatine into the body. Liquids, powders, tablets, gel caps, effervescent tablets, and even chewing gums are being used as a delivery mechanism of creatine. Creatine has been known about for 160 years, and was first used as a supplement in World War I by German scientist. It was given to German soldiers to reduce fatigue in combat.

What happens when Creatine is ingested?

When the body uptakes creatine into the body there are four documented effects. The first effect is the most important benefit of the product which is the quick transformation of ADP to ATP from creatine phosphate. This is important because in the human body there is an expendable amount of ATP, which will be consumed in ten to fifteen seconds of maximal exertion. Creatine can also help volumize muscle cells. Creatine helps pull water into muscle cells increasing their size. It is unclear if this effect has any benefits to enhance strength but the first effect is by far the most important. Recent studies also have shown of two more possible effects. Creatine has been show to buffer Lactic Acid build-up and enhance protein synthesis. These effects have not been tested enough and more research must be completed to determine their validity.

How much Creatine?

The amount of creatine per person varies depending on the persons weight and muscle mass. An average male weighing 160 pounds would have about 120 grams of creatine in their system. 95%-98% of this creatine would be stored in muscles and the other 2%-5% would be found in the brain, heart and testes. About two grams of creatinine, the waste product of creatine, would be excreted per day and half of this amount would be from liver synthesis. The other half would be from that persons diet. Many producers of the creatine supplement insist on loading with creatine for the first week. This loading dose could be as much as 20 grams per day. It has been shown that there are not great gains in strength, muscle mass, or indurance for those who load compared to those who don't load. The loading phase probably is just a scheme for the producers of the product to make more money. The recommended dose of creatine supplement is 5 grams per day. Creatine should be taken in cycles, meaning that it should be supplemented for a period of time and then that person should take a break from the supplementation.

Should Creatine be banned from athletic performances?

Creatine should not and could not be banned form athletic competitions. An athlete who consumes creatine can only hold about five grams of creatine per kilogram of muscle and this amount could be obtained through eating large quantities of meat and fish. The same waste product of creatine, creatinine, would be excreted in the urine and the competitor could not be excluded from competition. Creatine, one of the most widely known and used products has no immediate detrimental side effects. It has been one of the most widely analyzed and researched natural supplement and no evidence has been found that supplementation of this product, along with a well balance diet, is harmful. When one supplements with creatine it is necessary to drink plenty of water making sure not to put strain on the kidneys.

Related links

http://www.sportsci.org/traintech/creatine/rbk.html

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Creatine chemical structure of creatine What is Creatine? Creatine is an amino acid, with the chemical name methyl guanidine-acetic acid, that can be converted into the phosphocreatine. Phosphocreatine is storage mechanism muscle cells use to regenerate the cells primary source of energy adenosine triphosphate (ATP).

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Team Brown Rice!

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Find out how creatine might affect your athletic performance and how the supplement interacts with other drugs.

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What is creatine?

Creatine is a natural source of energy that helps your skeletal muscles flex (contract). It helps create a steady supply of energy in your muscles so they can keep working, especially while you're exercising.

About half of your body's supply of creatine (1 to 2 grams/day, about the size of 1 to 2 jellybeans) comes from your diet, especially protein-rich foods such as:

Red meat (pork, veal and beef).

Seafood (fish and shellfish).

Animal milk (like cow, goat and sheep milk).

Your body produces the other half naturally in your liver, kidneys and pancreas. They deliver about 95% of the creatine to your skeletal muscles to use during physical activity. The rest goes to your heart, brain and other tissues.

Manufacturers also make creatine supplements. Some people take creatine supplements because they work out a lot or don't get enough creatine in their diet. Creatine supplements exist as:

Is it healthy to take creatine?

Studies show that it's safe for many people to take creatine supplements. However, there isn't enough evidence to know if it's safe if you:

Are pregnant or breastfeeding (chestfeeding).

Have diabetes.

Have kidney disease.

Have liver disease.

If you have bipolar disorder, creatine may also increase your risk of mania.

Talk to a healthcare provider before taking creatine to ensure it's safe for you.

Does creatine make you gain muscle?

It depends. Studies show that regularly taking creatine, weightlifting and exercising can help increase muscle growth in people 18 to 30 years old. However, there isn't enough research to say that creatine helps develop muscle growth in people older than 65 or people with diseases that affect their muscles.

Why do people take creatine supplements?

Many amateur and professional athletes take creatine supplements to aid their workout routines and improve their recovery. Creatine creates "quick burst" energy and increased strength, which improves your performance without affecting your ability to exercise for longer periods (aerobic endurance).

Most athletes who take creatine supplements participate in power sports, including:

In addition, studies suggest that creatine supplements may help brain function in people 60 and older. This includes:

Short-term memory.

Reasoning.

Neuroprotection (keeping groups of nerve cells safe from injury or damage).

Researchers are still studying whether creatine supplements may help people with cognitive (mental) conditions, including dementia.

Talk to a healthcare provider before taking creatine supplements, regardless of your level of physical fitness, age or health.

Are creatine supplements recommended for athletes?

Many athletes use creatine supplements. Professional sports organizations, the International Olympic Committee (IOC) and the National Collegiate Athletic Association (NCAA) all allow athletes to use creatine supplements.

Men and women and people assigned male or female at birth ( AMAB or AFAB) report benefits to using creatine. But some studies note that women and people AFAB who take creatine supplements may not gain as much strength or muscle mass as men and people AMAB.

What is the most common type of creatine supplement?

The most common creatine supplement is creatine monohydrate. It's a dietary supplement that increases muscle performance in short-duration, high-intensity resistance exercises, such as weightlifting, sprinting and bicycling. Other forms of creatine don't appear to have these benefits.

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Creatine is one of your body's natural energy sources for muscle contraction. Many athletes take creatine supplements to increase strength and improve recovery.

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Team Buckwheat

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There is no recommended intake for creatine from the Food and Drug administration because it can be produced by the body. But eating adequate amounts of protein is critical to creatine production and research suggests that 10 to 30 percent of your total caloric intake should come from protein sources. This will help ensure that your body can produce enough creatine while providing other vital nutritional benefits.

Can athletes usually get enough creatine through food alone?

Yes, most athletes can get enough creatine from food alone. Your body makes creatine from three key amino acids: glycine, arginine, and methionine. And while red meat and salmon are great sources for amino acids and creatine, vegetarian-friendly eggs provide a massive amount of these amino acids as well.

According to the USDA, eating two eggs (roughly 100 grams) nets nearly 11 grams of protein, 422 mg of glycine, 691 mg of arginine, and 486 mg of methionine in addition to other essential amino acids. And eggs contain plenty of vitamins and minerals, including selenium, vitamin B12, vitamin D, and vitamin B2.

Is it better to get creatine from a supplement?

Most sports dietitians recommend a food-first approach to nutrition, and for most athletes, it's possible to consume enough protein through food sources. While creatine supplements may seem like an easy fix to meet your protein needs, there is always some amount of risk associated with using supplements because they are regulated post-market, meaning that no regulator evaluates the contents of supplements before they are sold. As such, products contaminated with potentially harmful and/or prohibited ingredients often reach consumers and it's impossible to tell from the supplement facts label if a product is safe to use.

If athletes choose to use supplements despite the risks, USADA has always recommended that athletes use only dietary supplements that have been certified by a third-party program that tests for substances prohibited in sport.

Why are supplements risky in general?

Unlike pharmaceuticals, the Food and Drug Administration (FDA) does not analyze the safety, efficacy, or label accuracy of supplements before they are sold to consumers. Manufacturers may misidentify prohibited substances on labels, or they may omit prohibited substances from labels altogether. And in some cases, dietary supplements with illegal or dangerous ingredients have remained on shelves for years despite FDA warnings and recall efforts. In 2021, Canadian company Genex Nutraceuticals recalled one of the brand's creatine batches for containing dangerous levels of vitamin D, which wasn't even listed on the label!

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Do Athletes Really Need Creatine Supplements? | U.S. Anti-Doping Agency (USADA)

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Creatine supplements are rarely essential for athletes since your body actually produces creatine on its own.

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Key facts

Vitamin B has many important functions in your body, including converting food to energy.

Each type of vitamin B has its own natural food sources. Many of them are animal-based (meat, fish and dairy).

Other natural sources of vitamin B include wholewheat bread, vegetables, nuts and yeast extracts.

A balanced diet will give you the nutrients you need to stay healthy and increase your quality of life.

Why should I include vitamin B in my diet?

Vitamin B should be a part of your diet. It helps your body function better, such as your metabolism (how your body converts food to energy). It also plays a vital role in your body's cellular processes.

Each type of vitamin B has a different but critical role in keeping you healthy. For example, B12, B6 and B9 are important vitamins for healthy brain and nerve function. Vitamin B2 is important for skin health and good vision.

Go here for more information on vitamin B and your health.

What are the best natural sources of vitamin B?

Thiamin (B1)

B1 is found in fish, meat, wholewheat breads, fortified cereals (cereals with added nutrients such as B1) and yeast extracts (such as Vegemite spread).

Riboflavin (B2)

B2 is found in dairy products (such as milk, yoghurt and cheese), yeast extracts, eggs, wholewheat bread and fortified cereals.

Niacin (B3)

B3 is found in meat, chicken, fish, nuts and yeast extracts.

Pantothenic acid (B5)

B5 is found in many foods, including liver, meats, milk, eggs, yeast, peanuts and legumes.

Pyridoxine (B6)

B6 is found in meat, fish, wholewheat foods, nuts and vegetables.

Biotin (B7)

B7 is found in liver, cauliflower, peanuts, chicken, yeast and mushrooms.

Folate (B9)

B9 is found in liver, legumes, wholewheat breads and cereals, and leafy green vegetables. The more that food is processed and cooked, the less folate it will have.

Cyanocobalamin (B12)

B12 is found in animal-based products (such as meat, fish, eggs and milk) and certain fortified cereals.

To have a diet high in B vitamins, try to eat a wide variety of fresh unprocessed foods, such as meat and other proteins, dairy, cereals, fruits and vegetables.

if you have a restricted diet, such as a vegan diet, you may be at risk of vitamin deficiency. You might need supplements to get enough B vitamins.

Before taking any vitamin supplement, speak with your doctor or an accredited dietician. While vitamins can supplement your diet, you still need to eat healthily.

What is a balanced diet?

To maintain a balanced diet, you should monitor what you eat and drink. Include a variety of nutritious foods from all five food groups every day.

The 5 food groups are:

vegetables and legumes/beans - at least 5 serves daily

fruit - 2 serves daily

lean meats and poultry, fish, eggs, tofu, nuts and seeds and legumes/beans - 1 to 3 serves a day, depending on your age (and during pregnancy, 3-4 serves a day are recommended)

milk, yoghurt cheese and/or alternatives, mostly reduced fat - at least 2-3 serves daily, with the minimum amount varying based on your age, sex and life stage

grain (cereal) foods, mostly wholegrain and/or high cereal fibre varieties - the number of daily wholegrain cereal serves you need varies based on your age and life stage, ranging from 4 serves daily for children to 6 serves daily for adult males under 70 years and adult females under 50 years of age

Aim to limit takeaway foods such as pizza and fried food to once weekly or less. Choose water rather than sugary drinks. Limit sweet foods like cakes and muffins, and salty, processed foods like salami and chips.

Drink no more than 2 standard alcoholic drinks per day. For pregnant and breastfeeding people, the safest option is to not drink any alcohol.

Last reviewed: May 2022

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Vitamin B helps your body function better, and plays a vital role in your body's cellular processes. Each type of vitamin B has a different but critical role in keeping you healthy - find out what foods are high in vitamin B here.

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About B-group vitamins

naturally occur in food and are needed in very small amounts for various bodily functions such as energy production and making red blood cells. There are 13 vitamins that our body needs, 8 of which make up the B-group (or B-complex) vitamins.

The B-group vitamins do not provide the body with fuel for energy, even though supplement advertisements often claim they do. However, it's true though that without B-group vitamins the body lacks energy. This is because the B-group vitamins are needed to help the body to use the energy-yielding nutrients (such as , and ) for fuel. Other B-group vitamins are needed to help cells to multiply by making new DNA.

Vitamin B in food

Even though the B-group vitamins are found in many foods, they are water soluble and are generally quite delicate. They are easily destroyed, particularly by and cooking.

can also reduce the amount of B-group vitamins in foods - either by destroying them, or in white flours, white breads and white rice removing the parts that contain the most B-group vitamins. This is one of the reasons white flours, white breads and white rice are less nutritious than their wholegrain counterparts.

The body has a limited capacity to store most of the B-group vitamins (except B12 and folate, which are stored in the liver). A person who has a poor diet for a few months may end up with B-group vitamins deficiency. For this reason, it's important that adequate amounts of these vitamins be eaten regularly as part of a well-balanced, nutritious diet.

Vitamin B supplements

Taking vitamins that your body does not need can mean, at a best-case scenario, that your body gets rid of the excess in your urine (so you waste your money). But some vitamins can also be toxic if taken incorrectly, so you could also be damaging your body instead of helping it.

Some B-group vitamins also work together in the body (for example, vitamin B12 and folate or folic acid). This means taking supplements can sometimes hide deficiencies of other vitamins, which can also lead to health problems.

Types of vitamin B

There are 8 types of vitamin B:

thiamin (B1)

riboflavin (B2)

niacin (B3)

pantothenic acid (B5)

pyridoxine (B6)

biotin (B7)

folate or 'folic acid' when included in supplements (B9)

cyanocobalamin (B12).

Thiamin (B1)

Thiamin is also known as vitamin B1. It helps to convert glucose into energy and has a role in nerve function.

Good sources of thiamin

In Australia, it's mandatory that white and wholemeal flour used for bread is .

Thiamin deficiency

Beriberi is a condition caused by thiamin deficiency and affects the cardiovascular, muscular, gastrointestinal and nervous systems. It can be classified as 'wet' and 'dry' beriberi. 'Dry' beriberi affects the nervous symptom while 'wet' beriberi affects the cardiovascular system.

Wernicke-Korsakoff syndrome (also called 'wet brain') is another thiamin-deficiency disease linked to alcohol excess and a thiamin-deficient diet. Alcohol reduces thiamin absorption in the gut and increases its excretion from the kidneys.

Riboflavin (B2)

Riboflavin is primarily involved in energy production and helps vision and skin health.

Good sources of riboflavin

yoghurt

cottage cheese

wholegrain breads and cereals

egg white

leafy green vegetables

yeast

liver

kidney.

Riboflavin deficiency (ariboflavinosis)

Riboflavin deficiency (or ariboflavinosis) is rare and is usually seen along with other B-group vitamin deficiencies. People at risk include those who consume excessive amounts of alcohol and those who do not consume milk or .

Niacin (B3)

Niacin is essential for the body to convert carbohydrates, fat and alcohol into energy. It helps maintain skin health and supports the nervous and digestive systems. Unlike other B-group vitamins, niacin is very heat stable and little is lost in cooking.

Good sources of niacin

Niacin deficiency (pellagra)

People who drink excessive amounts of alcohol or live on a diet almost exclusively based on corn are most at risk of pellagra. Others causes are associated with digestive problems where the body does not absorb niacin efficiently.

Excessive niacin intake

Large doses of niacin produce a drug-like effect on the nervous system and on blood fats. While favourable changes in blood fats are seen, side effects include flushing, itching, nausea and potential liver damage.

Pantothenic acid (B5)

Pantothenic acid is needed to metabolise carbohydrates, proteins, fats and alcohol as well as produce red blood cells and steroid hormones.

Good sources of pantothenic acid

Pantothenic acid is widespread and found in a range of foods, but some good sources include:

Pantothenic acid deficiency

Because pantothenic acid is found in such a wide variety of foods, deficiency is extremely rare.

Vitamin B6 (pyridoxine)

Pyridoxine is needed for protein and carbohydrate metabolism, the formation of red blood cells and certain brain chemicals. It influences brain processes and development, and steroid hormone activity.

Good sources of pyridoxine

Pyridoxine deficiency

Excessive pyridoxine intake

Pyridoxine toxicity is mostly due to supplementation and can lead to harmful levels in the body that can damage the nerves.

Biotin (B7)

Biotin (B7) is needed for energy , fat synthesis, amino acid metabolism and glycogen synthesis. High biotin intake can contribute to raised blood cholesterol levels.

Good sources of biotin

Biotin deficiency

Biotin deficiency is very rare - it's widely distributed in foods and only required in small amounts. Over-consumption of raw egg whites over periods of several months (by bodybuilders, for example) can induce deficiency because a protein in the egg white inhibits biotin absorption.

Folate or folic acid (B9)

Folate, or folic acid (the synthetic form of folate which is used extensively in dietary supplements and ) is needed to form red blood cells, which carry oxygen around the body. It helps the development of the , as well as DNA synthesis and cell growth. Women of child-bearing age need a diet rich in folate for this reason.

If , you should visit your doctor to make sure you're getting enough folate. This is important to reduce the risks of neural tube defects such as spina bifida in the baby.

Good sources of folate

Since 2009, all bread sold in Australia (except organic) has been fortified with folic acid.

Excessive folic acid intake

Although folic acid is generally considered non-toxic, excessive intakes above 1,000mcg per day over a period of time can lead to malaise, irritability and intestinal dysfunction. The main risk with excessive folate intake is that it can mask a vitamin B12 deficiency, so it's best to consume these 2 vitamins within the recommended amounts.

Cyanocobalamin (B12)

Cyanocobalamin (or vitamin B12) helps to produce and maintain the myelin surrounding nerve cells, mental ability, red blood cell formation and the breaking down of some fatty acids and amino acids to produce energy. Vitamin B12 has a close relationship with folate, as both depend on the other to work properly.

Good sources of B12

Vitamin B12 deficiency

Because vitamin B12 is only found in foods from animal sources, people following strict , as well as breastfed babies of vegan mothers, tend to be most commonly affected.

Absorption of B12 from the gut also tends to , so the elderly is another group who are more at risk of deficiency.

Where to get help

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The eight B-group vitamins are essential for various functions within the body.

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Dr. Matutes

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This is a fact sheet intended for health professionals. For a general overview of Vitamin B6, see our consumer fact sheet on Vitamin B6.

Introduction

Vitamin B6 in coenzyme forms performs a wide variety of functions in the body and is extremely versatile, with involvement in more than 100 enzyme reactions, mostly concerned with protein metabolism [ 1]. Both PLP and PMP are involved in amino acid metabolism, and PLP is also involved in the metabolism of one-carbon units, carbohydrates, and lipids [ 3]. Vitamin B6 also plays a role in cognitive development through the biosynthesis of neurotransmitters and in maintaining normal levels of homocysteine, an amino acid in the blood [ 3]. Vitamin B6 is involved in gluconeogenesis and glycogenolysis, immune function (for example, it promotes lymphocyte and interleukin-2 production), and hemoglobin formation [ 3].

The human body absorbs vitamin B6 in the jejunum. Phosphorylated forms of the vitamin are dephosphorylated, and the pool of free vitamin B6 is absorbed by passive diffusion [ 2].

Vitamin B6 concentrations can be measured directly by assessing concentrations of PLP; other vitamers; or total vitamin B6 in plasma, erythrocytes, or urine [ 1]. Vitamin B6 concentrations can also be measured indirectly by assessing either erythrocyte aminotransferase saturation by PLP or tryptophan metabolites. Plasma PLP is the most common measure of vitamin B6 status.

Recommended Intakes

Intake recommendations for vitamin B6 and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the FNB [ 1]. DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. These values, which vary by age and gender, include:

Recommended Dietary Allowance (RDA): Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%-98%) healthy individuals; often used to plan nutritionally adequate diets for individuals.

Adequate Intake (AI): Intake at this level is assumed to ensure nutritional adequacy; established when evidence is insufficient to develop an RDA.

Estimated Average Requirement (EAR): Average daily level of intake estimated to meet the requirements of 50% of healthy individuals; usually used to assess the nutrient intakes of groups of people and to plan nutritionally adequate diets for them; can also be used to assess the nutrient intakes of individuals.

Tolerable Upper Intake Level (UL): Maximum daily intake unlikely to cause adverse health effects.

Table 1 lists the current RDAs for vitamin B6 [ 1]. For infants from birth to 12 months, the FNB established an AI for vitamin B6 that is equivalent to the mean intake of vitamin B6 in healthy, breastfed infants.

* Adequate Intake (AI)

Sources of Vitamin B6

Food

Vitamin B6 is found in a wide variety of foods [ 1, 3, 4]. The richest sources of vitamin B6 include fish, beef liver and other organ meats, potatoes and other starchy vegetables, and fruit (other than citrus). In the United States, adults obtain most of their dietary vitamin B6 from fortified cereals, beef, poultry, starchy vegetables, and some non-citrus fruits [ 1, 3, 5]. About 75% of vitamin B6 from a mixed diet is bioavailable [ 1].

The table of selected food sources of vitamin B6 suggests many dietary sources of vitamin B6.

*DV = Daily Value. The U.S. Food and Drug Administration (FDA) developed DVs to help consumers compare the nutrient contents of foods and dietary supplements within the context of a total diet. The DV for vitamin B6 is 1.7 mg for adults and children age 4 years and older [ 6]. FDA does not require food labels to list vitamin B6 content unless vitamin B6 has been added to the food. Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet.

The U.S. Department of Agriculture's (USDA's) FoodData Central lists the nutrient content of many foods and provides a comprehensive list of foods containing vitamin B6 arranged by nutrient content and by food name.

Dietary supplements

About 28%-36% of the general population uses supplements containing vitamin B6 [ 9, 10]. Adults aged 51 years or older and children younger than 9 are more likely than members of other age groups to take supplements containing vitamin B6.

Vitamin B6 Intakes and Status

Most children, adolescents, and adults in the United States consume the recommended amounts of vitamin B6, according to an analysis of data from the 2003-2004 National Health and Nutrition Examination Survey (NHANES) [ 10]. The average vitamin B6 intake is about 1.5 mg/day in women and 2 mg/day in men [ 1].

However, 11% of vitamin B6 supplement users and 24% of people in the United States who do not take supplements containing vitamin B6 have low plasma PLP concentrations (less than 20 nmol/L) [ 10]. In the 2003-2004 NHANES analysis, plasma PLP concentrations were low even in some groups that took 2.0-2.9 mg/day, which is higher than the current RDA. Among supplement users and nonusers, plasma PLP levels were much lower in women than men, non-Hispanic blacks than non-Hispanic whites, current smokers than never smokers, and people who were underweight than those of normal weight. Teenagers had the lowest vitamin B6 concentrations, followed by adults aged 21-44 years. However, plasma PLP levels in the elderly were not particularly low, even in those who did not use supplements. Based on these data, the authors of this analysis concluded that the current RDAs might not guarantee adequate vitamin B6 status in many population groups [ 10].

PLP concentrations tend to be low in people with alcohol dependence; those with obesity; and pregnant people, especially those with preeclampsia or eclampsia [ 1]. They are also low in people with malabsorption syndromes such as celiac disease, Crohn's disease, and ulcerative colitis [ 3].

Vitamin B6 Deficiency

Isolated vitamin B6 deficiency is uncommon; inadequate vitamin B6 status is usually associated with low concentrations of other B-complex vitamins, such as vitamin B12 and folic acid [ 2]. Vitamin B6 deficiency causes biochemical changes that become more obvious as the deficiency progresses [ 2].

End-stage renal diseases, chronic renal insufficiency, and other kidney diseases can cause vitamin B6 deficiency [ 3]. In addition, vitamin B6 deficiency can result from malabsorption syndromes, such as celiac disease, Crohn's disease, and ulcerative colitis. Certain genetic diseases, such as homocystinuria, can also cause vitamin B6 deficiency [ 2]. Some medications, such as antiepileptic drugs, can lead to deficiency over time.

Groups at Risk of Vitamin B6 Inadequacy

Frank vitamin B6 deficiencies are relatively rare in the United States but some individuals might have marginal vitamin B6 status [ 2]. The following groups are among those most likely to have inadequate intakes of vitamin B6.

Individuals with Impaired Renal Function

Individuals with Autoimmune Disorders

Patients with celiac disease, Crohn's disease, ulcerative colitis, inflammatory bowel disease, and other malabsorptive autoimmune disorders tend to have low plasma PLP concentrations [ 3]. The mechanisms for this effect are not known. However, celiac disease is associated with lower pyridoxine absorption, and low PLP concentrations in inflammatory bowel disease could be due to the inflammatory response [ 3].

People with Alcohol Dependence

Plasma PLP concentrations tend to be very low in people with alcohol dependence [ 1]. Alcohol produces acetaldehyde, which decreases net PLP formation by cells and competes with PLP in protein binding [ 1, 3]. As a result, the PLP in cells might be more susceptible to hydrolysis by membrane-bound phosphatase. People with alcohol dependence might benefit from pyridoxine supplementation [ 3].

Vitamin B6 and Health

Cardiovascular Disease

The research to date provides little evidence that supplemental amounts of vitamin B6, alone or with folic acid and vitamin B12, can help reduce the risk or severity of cardiovascular disease and stroke.

Cancer

Some research has associated low plasma vitamin B6 concentrations with an increased risk of certain kinds of cancer [ 3]. For example, a meta-analysis of prospective studies found that people with a vitamin B6 intake in the highest quintile had a 20% lower risk of colorectal cancer than those with an intake in the lowest quintile [ 17].

However, the small number of clinical trials completed to date has not shown that vitamin B6 supplementation can help prevent cancer or reduce its impact on mortality. For example, an analysis of data from two large randomized, double-blind, placebo-controlled trials in Norway found no association between vitamin B6 supplementation and cancer incidence, mortality, or all-cause mortality [ 18].

Cognitive Function

Poor vitamin B6 status has been hypothesized to play a role in the cognitive decline that some older adults experience [ 19]. Several studies have demonstrated an association between vitamin B6 and brain function in the elderly. For example, an analysis of data from the Boston Normative Aging Study found associations between higher serum vitamin B6 concentrations and better memory test scores in 70 men aged 54-81 years [ 20].

However, a systematic review of 14 randomized controlled trials found insufficient evidence of an effect of vitamin B6 supplementation alone or in combination with vitamin B12 and/or folic acid on cognitive function in people with normal cognitive function, dementia, or ischemic vascular disease [ 19]. According to this review, most of the studies were of low quality and limited applicability. A Cochrane review found no evidence that short-term vitamin B6 supplementation (for 5-12 weeks) improves cognitive function or mood in the two studies that the authors evaluated [ 21]. The review did find some evidence that daily vitamin B6 supplements (20 mg) can affect biochemical indices of vitamin B6 status in healthy older men, but these changes had no overall impact on cognition.

More evidence is needed to determine whether vitamin B6 supplements might help prevent or treat cognitive decline in elderly people.

Premenstrual Syndrome

Some evidence suggests that vitamin B6 supplements could reduce the symptoms of premenstrual syndrome (PMS), but conclusions are limited due to the poor quality of most studies [ 22]. A meta-analysis of nine published trials involving almost 1,000 women with PMS found that vitamin B6 is more effective in reducing PMS symptoms than placebo, but most of the studies analyzed were small and several had methodological weaknesses [ 22]. A more recent double-blind, randomized controlled trial in 94 women found that 80 mg pyridoxine taken daily over the course of three cycles was associated with statistically significant reductions in a broad range of PMS symptoms, including moodiness, irritability, forgetfulness, bloating, and, especially, anxiety [ 23]. The potential effectiveness of vitamin B6 in alleviating the mood-related symptoms of PMS could be due to its role as a cofactor in neurotransmitter biosynthesis [ 24]. Although vitamin B6 shows promise for alleviating PMS symptoms, more research is needed before drawing firm conclusions.

Nausea and Vomiting in Pregnancy

About half of all individuals experience nausea and vomiting in the first few months of pregnancy, and about 50%-80% experience nausea only [ 25, 26]. Although this condition is generally known as "morning sickness," it often lasts throughout the day. The condition is not life threatening and typically goes away after 12-20 weeks, but its symptoms can disrupt a person's social and physical functioning.

Randomized trials have shown that a combination of vitamin B6 and doxylamine (an antihistamine) is associated with a 70% reduction in nausea and vomiting in pregnant individuals and lower hospitalization rates for this problem [ 25, 29].

The American Congress of Obstetrics and Gynecology (ACOG) recommends monotherapy with 10-25 mg of vitamin B6 three or four times a day to treat nausea and vomiting in pregnancy [ 29]. If the patient's condition does not improve, ACOG recommends adding doxylamine. Before taking a vitamin B6 supplement, pregnant people should consult a physician because doses could approach the UL.

Health Risks from Excessive Vitamin B6

High intakes of vitamin B6 from food sources have not been reported to cause adverse effects [ 1]. However, chronic administration of 1-6 g oral pyridoxine per day for 12-40 months can cause severe and progressive sensory neuropathy characterized by ataxia (loss of control of bodily movements) [ 10, 30-33]. Symptom severity appears to be dose dependent, and the symptoms usually stop if the patient discontinues the pyridoxine supplements as soon as the neurologic symptoms appear. Other effects of excessive vitamin B6 intakes include painful, disfiguring dermatological lesions; photosensitivity; and gastrointestinal symptoms, such as nausea and heartburn [ 1, 2, 30].

The scientific literature includes isolated case reports of congenital defects in the infants of individuals who took pyridoxine supplements during the first half of pregnancy [ 7]. However, a more recent observational study found no association between pyridoxine supplementation (mean dose 132.3 ± 74 mg/day) in pregnant people starting at 7 weeks gestation and continuing for 9 ± 4.2 weeks and teratogenic effects in their infants [ 34].

The FNB has established ULs for vitamin B6 that apply to both food and supplement intakes (Table 3) [ 1]. The FNB noted that although several reports show sensory neuropathy occurring at doses lower than 500 mg/day, studies in patients treated with vitamin B6 (average dose of 200 mg/day) for up to 5 years found no evidence of this effect. Based on limitations in the data on potential harms from long-term use, the FNB halved the dose used in these studies to establish a UL of 100 mg/day for adults. ULs are lower for children and adolescents based on body size. The ULs do not apply to individuals receiving vitamin B6 for medical treatment, but such individuals should be under the care of a physician.

*Breast milk, formula, and food should be the only sources of vitamin B6 for infants.

In 2023, the Panel on Nutrition, Novel Foods and Food Allergens of the European Food Safety Authority (EFSA) released a scientific opinion on the tolerable upper intake levels for vitamin B6 [ 35]. Based on systematic reviews that examined associations between vitamin B6 and peripheral neuropathy, the panel set an upper limit for vitamin B6 of 12 mg/day for all adults, including those who are pregnant or lactating, with lower amounts ranging from 2.2 to 10.7 mg/day for infants and children, depending on age.

Interactions with Medications

Vitamin B6 can interact with certain medications, and several types of medications might adversely affect vitamin B6 levels. A few examples are provided below. Individuals taking these and other medications on a regular basis should discuss their vitamin B6 status with their health care providers.

Cycloserine

Cycloserine (Seromycin®) is a broad-spectrum antibiotic used to treat tuberculosis. In combination with pyridoxal phosphate, cycloserine increases urinary excretion of pyridoxine [ 9]. The urinary loss of pyridoxine might exacerbate the seizures and neurotoxicity associated with cycloserine. Pyridoxine supplements can help prevent these adverse effects.

Antiepileptic Medications

Some antiepileptic drugs, including valproic acid (Depakene®, Stavzor®), carbamazepine (Carbatrol®, Epitol®, Tegretol®, and others), and phenytoin (Dilantin®) increase the catabolism rate of vitamin B6 vitamers, resulting in low plasma PLP concentrations and hyperhomocysteinemia [ 36, 37]. High homocysteine levels in antiepileptic drug users might increase the risk of epileptic seizures and systemic vascular events, including stroke, and reduce the ability to control seizures in patients with epilepsy. Furthermore, patients typically use antiepileptic drugs for years, increasing their risk of chronic vascular toxicity.

Theophylline

Theophylline (Aquaphyllin®, Elixophyllin®, Theolair®, Truxophyllin®, and many others) can prevent or treat shortness of breath, wheezing, and other breathing problems caused by asthma, chronic bronchitis, emphysema, and other lung diseases. Patients treated with theophylline often have low plasma PLP concentrations, which could contribute to the neurological and central nervous system side effects associated with theophylline, including seizures [ 9, 33].

Vitamin B6 and Healthful Diets

The federal government's 2020-2025 Dietary Guidelines for Americans notes that "Because foods provide an array of nutrients and other components that have benefits for health, nutritional needs should be met primarily through foods. ... In some cases, fortified foods and dietary supplements are useful when it is not possible otherwise to meet needs for one or more nutrients (e.g., during specific life stages such as pregnancy)."

For more information about building a healthy dietary pattern, refer to the Dietary Guidelines for Americans and the U.S. Department of Agriculture's MyPlate.

The Dietary Guidelines for Americans describes a healthy dietary pattern as one that:

Includes a variety of vegetables; fruits; grains (at least half whole grains); fat-free and low-fat milk, yogurt, and cheese; and oils.
Many fruits, vegetables, and whole grains are good sources of vitamin B6. Some ready-to-eat breakfast cereals are fortified with vitamin B6.

Includes a variety of protein foods such as lean meats; poultry; eggs; seafood; beans, peas, and lentils; nuts and seeds; and soy products.
Fish, beef, and turkey contain high amounts of vitamin B6. Beans and nuts are also sources of vitamin B6.

Limits foods and beverages higher in added sugars, saturated fat, and sodium.

Limits alcoholic beverages.

Stays within your daily calorie needs.

1. Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes: Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline . Washington, DC: National Academy Press; 1998.

2. McCormick D. Vitamin B6. In: Bowman B, Russell R, eds. Present Knowledge in Nutrition. 9th ed. Washington, DC: International Life Sciences Institute; 2006.

3. Mackey A, Davis S, Gregory J. Vitamin B6. In: Shils M, Shike M, Ross A, Caballero B, Cousins R, eds. Modern Nutrition in Health and Disease. 10th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2005.

4. U.S. Department of Agriculture, Agricultural Research Service. FoodData Central , 2019.

5. Subar AF, Krebs-Smith SM, Cook A, Kahle LL. Dietary sources of nutrients among US adults, 1989 to 1991. J Am Diet Assoc 1998;98:537-47. [PubMed abstract]

6. U.S. Food and Drug Administration. Food Labeling: Revision of the Nutrition and Supplement Facts Labels. 2016.

7. Natural Medicines Comprehensive Database . Vitamin B6. 2011.

8. Simpson JL, Bailey LB, Pietrzik K, Shane B, Holzgreve W. Micronutrients and women of reproductive potential: required dietary intake and consequences of dietary deficiency or excess. Part I--Folate, Vitamin B12, Vitamin B6. J Matern Fetal Neonatal Med 2010;23:1323-43. [PubMed abstract]

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16. Toole JF, Malinow MR, Chambless LE, Spence JD, Pettigrew LC, Howard VJ, et al. Lowering homocysteine in patients with ischemic stroke to prevent recurrent stroke, myocardial infarction, and death: the Vitamin Intervention for Stroke Prevention (VISP) randomized controlled trial. JAMA 2004;291:565-75. [PubMed abstract]

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23. Kashanian M, Mazinani R, Jalalmanesh S. Pyridoxine (vitamin B6) therapy for premenstrual syndrome. Int J Gynaecol Obstet 2007;96:43-4. [PubMed abstract]

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27. Vutyavanich T, Wongtra-ngan S, Ruangsri R. Pyridoxine for nausea and vomiting of pregnancy: a randomized, double-blind, placebo-controlled trial. Am J Obstet Gynecol 1995;173:881-4. [PubMed abstract]

28. Sahakian V, Rouse D, Sipes S, Rose N, Niebyl J. Vitamin B6 is effective therapy for nausea and vomiting of pregnancy: a randomized, double-blind placebo-controlled study. Obstet Gynecol 1991;78:33-6. [PubMed abstract]

29. ACOG (American College of Obstetrics and Gynecology) Practice Bulletin: nausea and vomiting of pregnancy. Obstet Gynecol 2004;103:803-14. [PubMed abstract]

30. Bendich A, Cohen M. Vitamin B6 safety issues. Ann N Y Acad Sci 1990;585:321-30. [PubMed abstract]

31. Gdynia HJ, Muller T, Sperfeld AD, Kuhnlein P, Otto M, Kassubek J, et al. Severe sensorimotor neuropathy after intake of highest dosages of vitamin B6. Neuromuscul Disord 2008;18:156-8. [PubMed abstract]

32. Perry TA, Weerasuriya A, Mouton PR, Holloway HW, Greig NH. Pyridoxine-induced toxicity in rats: a stereological quantification of the sensory neuropathy. Exp Neurol 2004;190:133-44. [PubMed abstract]

33. Bender DA. Non-nutritional uses of vitamin B6. Br J Nutr 1999;81:7-20. [PubMed abstract]

34. Shrim A, Boskovic R, Maltepe C, Navios Y, Garcia-Bournissen F, Koren G. Pregnancy outcome following use of large doses of vitamin B6 in the first trimester. J Obstet Gynaecol 2006;26:749-51. [PubMed abstract]

35. EFSA NDA Panel (EFSA Panel on Nutrition, Novel Foods and Food Allergens), Turck, D, Bohn, T, Castenmiller, J, de Henauw, et al. Scientific opinion on the tolerable upper intake level for vitamin B6. EFSA Journal 2023; 21(5):8006, 110 pp.

36. Clayton PT. B6-responsive disorders: a model of vitamin dependency. J Inherit Metab Dis 2006;29:317-26. [PubMed abstract]

37. Apeland T, Froyland ES, Kristensen O, Strandjord RE, Mansoor MA. Drug-induced pertubation of the aminothiol redox-status in patients with epilepsy: improvement by B-vitamins. Epilepsy Res 2008;82:1-6. [PubMed abstract]

38. Hansson O, Sillanpaa M. Letter: Pyridoxine and serum concentration of phenytoin and phenobarbitone. Lancet 1976;1:256. [PubMed abstract]

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40. Davis GP, McCarthy JT, Magill DB, Coffey B. Behavioral effects of levetiracetam mitigated by pyridoxine. J Child Adolesc Psychopharmacol 2009;19:209-11. [PubMed abstract]

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42. Major P, Greenberg E, Khan A, Thiele EA. Pyridoxine supplementation for the treatment of levetiracetam-induced behavior side effects in children: preliminary results. Epilepsy Behav. 2008 Oct;13(3):557-9. [PubMed abstract]

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Office of Dietary Supplements - Vitamin B6

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Benefits of Plant-Based Diets in Athletic Performance | The Public Health Advocate

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This article was originally published in our Spring 2021 print issue. Today, there are several elite athletes who successfully compete and win while eating a plant-based diet. From tennis player Venus Williams to basketball player Kyrie Irving to ultramarathoner Scott Jurek, athletes who compete at

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The United States Olympic & Paralympic Committee’s sport nutrition team is uniquely positioned to bring today’s best practices to the forefront. Each sport dietitian within the team brings a high level of expertise to the sports they support. They util…

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Athletes who want a winning edge need the right nutrition. When you give your body the right fuel by drinking enough water and eating a balanced diet, you will make the most of your athletic talents and gain more strength, power, and endurance when you train.

This article contains some general sports nutrition guidelines. To achieve top performance, your diet should be based on a variety of factors including your age, weight, physical condition, and the type of exercise you are doing. Consult your doctor for individualized sports nutrition advice.

Water is the most important nutrient for athletes. Water comprises about 60% of body weight and is essential for almost every bodily function. Because your body cannot make or store water, you must replace the water that you lose in your urine and sweat.

Everyone should drink at least two quarts (64 oz.) of water each day-and athletes need even more. To stay hydrated and avoid overheating, drink plenty of fluids before, during, and after sports or exercise. When you work out or compete, especially in hot weather, try to replace the amount of water you lose in sweat by drinking the same amount of fluid.

Drinking cool water is the best way to keep hydrated during workouts or events that last an hour or less. Sports drinks made up of 6% to 10% carbohydrates can help you stay hydrated during longer events. Most sports drinks should be diluted with approximately 50% water.

Because thirst is not a reliable way to tell if you need water, be sure to drink even if you are not thirsty. You will not start feeling thirsty until you have already lost about 2% of your body weight-enough to hurt performance. Also, if you stop drinking water as soon as your thirst is satisfied, you will get only about half the amount you really need.

The following tips will help you stay hydrated:

Drink small amounts of water frequently rather than large amounts less often.

Drink cool beverages to lower your core body temperature and reduce sweating.

Track your sweat loss by weighing yourself both before and after exercise. For every pound lost through sweat, drink 16 to 24 oz. of water. Your body weight should be back to normal before your next workout.

Pay attention to the amount and color of your urine. A large volume of clear urine is a sign that you are well-hydrated. Smaller amounts of urine, or dark or concentrated-appearing yellow urine can indicate dehydration. If your urine turns brown, it may be a sign of a more serious problem and you should get medical attention immediately.

A balanced diet is another key to sports nutrition. Eating the right combination of fuel (calories) from carbohydrates, proteins, and fats will give you energy for top performance.

Start your exercise or competition with glycogen-loaded muscles by eating carbohydrates for at least several days before the event.

To replenish energy and delay fatigue, eat additional carbohydrates when you exercise or compete for longer than one hour.

Level of fitness. Physically active people need more protein than those who do not exercise. You also need more protein when you start an exercise program.

Exercise type, intensity, and duration. Endurance athletes often burn protein for fuel, as do bodybuilders and other athletes who perform intense strength-building activities.

Total daily calories. Your body burns more protein if you do not consume enough calories to maintain your body weight. This can happen if you eat too little or exercise too much.

Carbohydrate intake. Your body may use protein for energy if you exercise with low levels of muscle glycogen or if you do repeated training sessions without eating more carbohydrates. When you start with enough muscle glycogen, protein supplies about 5% of your energy; otherwise, it may supply up to 10%.

What you eat several days before an endurance activity affects performance. The food you eat on the morning of a sports competition can ward off hunger, keep blood sugar levels adequate, and aid hydration. Try to avoid eating high-protein or high-fat foods on the day of an event.

To perform at your highest level, follow these general nutrition guidelines before an event:

Eat a meal high in carbohydrates.

Eat solid foods 3 to 4 hours before an event. Drink liquids 2 to 3 hours before an event.

Choose easily digestible foods, rather than fried or high-fat foods.

Avoid sugary foods and drinks within one hour of the event.

Drink enough fluids to ensure hydration. A good guideline to follow is: Drink 20 oz. of water 1 to 2 hours before exercise and an additional 10 to 15 oz. within 15 to 30 minutes of the event. Replenishing fluids lost to sweat is the primary concern during an athletic event. Drink 3 to 6 ounces of water or diluted sports drink every 10 to 20 minutes throughout competition.

First, exercise to muscle fatigue. Your workout must be identical to the upcoming event to deplete the right muscles.

Next, eat a high-carbohydrate diet (70% to 80% carbohydrates, 10% to 15% protein, and 10% to15% fat), and do little or no exercise for three days before the event.

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Athletes who want a winning edge need the right nutrition. When you give your body the right fuel by drinking enough water and eating a balanced diet, you will make the most of your athletic talents and gain more strength, power, and endurance when you train.

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Sport is supposed to be competitive. Athletes want to win, and want to perform at their best. Performance-enhancing drugs, however, should never be the answer, as they cheat the integrity of the game, opponents, fans, and athletes themselves. They also pose a very real danger to those who use them. They can lead to some very scary health consequences and, in some cases, are deadly.

Fortunately, for the overwhelming majority of athletes who choose to compete clean, athletes can still strive to reach peak performance honestly and with integrity. In addition to practicing hard, proper sleep, and recovery, athletes have long known that adding optimal dietary and hydration methods to their daily routines will allow them to get the most out of their bodies.

In consultation with registered dietitians, USADA and its program provide an optimal dietary intake guide for those looking to reach their full potential naturally.

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Sports Nutrition Guide | U.S. Anti-Doping Agency (USADA)

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An optimal dietary intake guide for athletes looking to increase performance and ability naturally and drug free. Carbohydrates, Hydration, Supplements...

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Eating for Exercise and Sports | Nutrition.gov

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Find information on nutrition and athletic performance.

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Language: English | French

Laura K Purcell and Canadian Paediatric Society, Paediatric Sports and Exercise Medicine Section

Abstract

Nutrition is an important part of sport performance for young athletes, in addition to allowing for optimal growth and development. Macronutrients, micronutrients and fluids in the proper amounts are essential to provide energy for growth and activity. To optimize performance, young athletes need to learn what, when and how to eat and drink before, during and after activity.

Keywords: Adolescents, Athletes, Children, Nutrition, Sports

Résumé

La nutrition est une partie importante de la performance sportive des jeunes athlètes, sans compter qu'elle favorise une croissance et un développement optimaux. Il est essentiel de consommer la bonne quantité de macronutriments, de micronutriments et de liquides pour fournir l'énergie nécessaire à la croissance et aux activités. Pour optimiser leur performance, les jeunes athlètes doivent apprendre quoi, quand et comment manger et boire avant, pendant et après l'activité.

Français en page 203
Proper nutrition is vital for child and adolescent athletes to attain proper growth and perform optimally in sports. Young athletes need to learn what foods are good for energy, when to eat certain foods, how to eat during an event, and when and what to eat to replenish after activity. A well-balanced diet containing appropriate amounts of macronutrients (protein, carbohydrates and fat) and micronutrients (vitamins and minerals) is essential to provide enough energy for growth and activity. Fluids are also essential for hydration to support growth and athletic performance.

ENERGY REQUIREMENTS

Basic nutrition is important for growth, achieving good health and scholastic achievement, and providing energy ( 1). Sports nutrition enhances athletic performance by decreasing fatigue and the risk of disease and injury; it also enables athletes to optimize training and recover faster ( 1). Balancing energy intake with energy expenditure is crucial to prevent an energy deficit or excess. Energy deficits can cause short stature, delayed puberty, menstrual dysfunction, loss of muscle mass and increased susceptibility for fatigue, injury or illness ( 2, 3). Energy excess can result in overweight and obesity ( 4).

Before puberty, minimum nutritional and energy requirements (caloric needs) are similar for boys and girls. Energy requirements for adolescents are more variable, depending on age, activity level, growth rate and stage of physical maturity ( Table 1 ) ( 1). These recommended energy allowances are the minimum necessary to ensure proper growth and bodily functions. Extra calories are needed during growth spurts and to replenish energy expended during athletic endeavours ( 1, 5, 6). For example, a 30 kg girl playing soccer for 60 min would expend an average of 270 calories, or a 60 kg boy playing ice hockey for 60 min would expend an average of 936 calories ( 6).

MACRONUTRIENTS

Macronutrients, such as carbohydrates, protein and fats, provide the fuel for physical activity and sports participation.

Carbohydrates

Carbohydrates are the most important fuel source for athletes because they provide the glucose used for energy. One gram of carbohydrate contains approximately four kilocalories of energy. Glucose is stored as glycogen in muscles and liver. Muscle glycogen is the most readily available energy source for working muscle and can be released more quickly than other energy sources ( 1). Carbohydrates should comprise 45% to 65% of total caloric intake for four- to 18-year-olds ( 1, 7). Good sources of carbohydrates include whole grains, vegetables, fruits, milk and yogurt.

Protein

Proteins build and repair muscle, hair, nails and skin. For mild exercise and exercise of short duration, proteins do not act as a primary source of energy. However, as exercise duration increases, proteins help to maintain blood glucose through liver gluconeogenesis ( 2). One gram of protein provides four kilocalories of energy. Protein should comprise approximately 10% to 30% of total energy intake for four- to 18-year-olds (7). Good sources of protein include lean meat and poultry, fish, eggs, dairy products, beans and nuts, including peanuts.

Fats

Fat is necessary to absorb fat-soluble vitamins (A, D, E, K), to provide essential fatty acids, protect vital organs and provide insulation. Fat also provides the feeling of satiety. It is a calorie-dense source of energy (one gram provides nine kilocalories) but is more difficult to use. Fats should comprise 25% to 35% of total energy intake for four- to 18-year-olds ( 7). Saturated fats should comprise no more than 10% of total energy intake ( 1, 3). Good sources of fat include lean meat and poultry, fish, nuts, seeds, dairy products, and olive and canola oils. Fat from chips, candy, fried foods and baked goods should be minimized.

MICRONUTRIENTS

Although there are many vitamins and minerals required for good health, particular attention should be devoted to ensuring that athletes consume proper amounts of calcium, vitamin D and iron. Calcium is important for bone health, normal enzyme activity and muscle contraction. The daily recommended intake of calcium is 1000 mg/day for four- to eight-year-olds and 1300 mg/day for nine- to 18-year-olds ( 7, 8). Calcium is contained in a variety of foods and beverages, including milk, yogurt, cheese, broccoli, spinach and fortified grain products.

Vitamin D is necessary for bone health and is involved in the absorption and regulation of calcium. Current recommendations suggest 600 IU/day for four- to 18-year-olds ( 8). Normal values of vitamin D also vary depending on geographical location and race. Athletes living in northern latitudes or who train indoors (eg, figure skaters, gymnasts, dancers) are more likely to be vitamin D deficient ( 2). Sources of vitamin D include fortified foods, such as milk, and sun exposure. Dairy products other than milk, such as yogurt, do not contain vitamin D.

Iron is important for oxygen delivery to body tissues. During adolescence, more iron is required to support growth as well as increases in blood volume and lean muscle mass ( 1). Boys and girls nine to 13 years of age should ingest 8 mg/day to avoid depletion of iron stores and iron-deficiency anemia ( 7). Adolescents 14 to 18 years of age require more iron, up to 11 mg/day for males and 15 mg/day for females ( 7). Iron depletion is common in athletes because of diets poor in meat, fish and poultry, or increased iron losses in urine, feces, sweat or menstrual blood ( 2). Therefore, athletes, particularly female athletes, vegetarians and distance runners should be screened periodically for iron status ( 2). Iron-rich foods include eggs, leafy green vegetables, fortified whole grains and lean meat.

FLUIDS

Fluids, particularly water, are important nutrients for athletes. Athletic performance can be affected by what, how much and when an athlete drinks. Fluids help to regulate body temperature and replace sweat losses during exercise ( 8, 9). Environmental temperature and humidity can affect how much an athlete sweats and how much fluid intake is required ( 1, 9, 10). Hotter temperatures and higher humidity make a person sweat more, and more fluid is needed to maintain hydration. Dehydration can decrease performance and put athletes at risk for heat exhaustion or heat stroke ( 1, 9, 10).

Proper hydration requires fluid intake before, during and after exercise or activity. The amount of fluid required depends on many factors, including age and body size ( 9, 10) ( Table 2 ). Before activity, athletes should consume 400 mL to 600 mL of cold water 2 h to 3 h before their event ( 1, 2, 10). During sporting activities, athletes should consume 150 mL to 300 mL of fluid every 15 min to 20 min ( 1, 2, 10). For events lasting less than 1 h, water is sufficient ( 4). For events lasting longer than 60 min, and/or taking place in hot, humid weather, sports drinks containing 6% carbohydrates and 20 mEq/L to 30 mEq/L of sodium chloride are recommended to replace energy stores and fluid/electrolyte losses ( 3, 4, 5, 9). Following activity, athletes should drink enough fluid to replace sweat losses ( Table 2 ). This usually requires consuming approximately 1.5 L of fluid/kg of body weight lost ( 1, 10). The consumption of sodium-containing fluids and snacks after exercise helps with rehydration by stimulating thirst and fluid retention ( 1, 2, 10). For non-athletes, routine ingestion of carbohydrate-containing sports drinks can result in consumption of excessive calories, increasing the risks of overweight and obesity, as well as dental caries and, therefore, should be avoided ( 4).

TABLE 2

Body weight, kg

Fluid replacement during exercise, mL/h

Fluid replacement after exercise, mL/h

RECOVERY FOODS

Recovery foods should be consumed within 30 min of exercise, and again within 1 h to 2 h of exercise, to help reload muscles with glycogen and allow for proper recovery. These foods should include protein and carbohydrates ( 2, 6). Examples include graham crackers with peanut butter and juice, yogurt with fruit, or a sports drink with fruit and cheese ( 6).

MEAL PLANNING

One of the trickiest things to manage is meal planning around athletic events. The timing of meals is very important and needs to be individualized. It is important for athletes to discover which foods they like that also help to maximize performance. They should not experiment with new foods or new routines on the day of competition.

General guidelines include eating meals a minimum of 3 h before an event to allow for proper digestion and to minimize incidence of gastrointestinal upset during exercise. Meals should include carbohydrates, protein and fat. Fibre should be limited. High-fat meals should be avoided before exercise because they can delay gastric-emptying, make athletes feel sluggish and thereby adversely affect performance ( 2, 6). For early morning practices or events, having a snack or liquid meal 1 h to 2 h before exercise, followed by a full breakfast after the event, will help ensure sufficient energy to maximize performance ( 2, 6).

Pre-game snacks or liquid meals should be ingested 1 h to 2 h before an event to allow for digestion before start of exercise ( 2, 6). Snacks can include fresh fruit, dried fruit, a bowl of cereal with milk, juice or fruit-based smoothies. During an event, sports drinks, fruit or granola bars can be ingested to help refuel and keep energy levels high.

REACHING THE FINISH LINE

A well-balanced diet is essential for growing athletes to maintain proper growth and optimize performance in athletic endeavours. An ideal diet comprises 45% to 65% carbohydrates, 10% to 30% protein and 25% to 35% fat. Fluids are very important for maintaining hydration and should be consumed before, during and after athletic events to prevent dehydration. Timing of food consumption is important to optimize performance. Meals should be eaten a minimum of 3 h before exercise and snacks should be eaten 1 h to 2 h before activity. Recovery foods should be consumed within 30 min of exercise and again within 1 h to 2 h of activity to allow muscles to rebuild and ensure proper recovery.

Acknowledgments

This practice point has been reviewed by the Canadian Paediatric Society's Nutrition and Gastroenterology Committee.

Footnotes

CPS PAEDIATRIC SPORTS AND EXERCISE MEDICINE EXECUTIVE
Neil Cooper MD (Member at large); David Fecteau MD (Secretary-treasurer); Erika Persson MD (Member at large); John F Philpott MD (President-elect); Laura K Purcell MD (President); Eric Koelink MD (Liaison, CPS Residents Section); David W Warren MD (former Liaison, CPS Emergency Medicine Section)

Principal author: Laura K Purcell MD

The recommendations in this document do not indicate an exclusive course of treatment or procedure to be followed. Variations, taking into account individual circumstances, may be appropriate. All Canadian Paediatric Society position statements and practice points are reviewed on a regular basis. Retired statements are removed from the website. Please consult the Position Statements section of the CPS website ( www.cps.ca) for the full-text, current version.

REFERENCES

6. Litt A. Fuel for young athletes: Essential foods and fluids for future champions. Windsor: Human Kinetics; 2004. [ Google Scholar]

Articles from Paediatrics & Child Health are provided here courtesy of Oxford University Press

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The Nutrition Facts label reflects current scientific information, including the link between diet and chronic diseases such as obesity and heart disease. The label makes it easier for you and your audience to make more informed food choices.

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