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Caffeine is a natural stimulant found in coffee beans, tea leaves, and cacao pods. It's also added to many sodas and energy drinks. When you consume caffeine, it affects your brain and central nervous system, making you feel more alert and less tired. Did you know that about 80% of the world's population consumes caffeine daily?

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Think of your brain like a busy classroom. Throughout the day, a chemical called adenosine builds up (like students getting tired). Caffeine blocks adenosine from doing its job - kind of like how a substitute teacher might change up the regular routine! This is why you feel more awake after drinking caffeinated beverages.

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Let's look at where we commonly find caffeine in our daily lives:
- Coffee (95-200 mg per cup)
- Tea (14-70 mg per cup)
- Soft drinks (35-45 mg per can)
- Energy drinks (70-150 mg per can)
- Chocolate (9-45 mg per 1.5 oz)
Keep these numbers in mind as we explore the pros and cons!

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Caffeine can help improve your memory and concentration! Research shows that moderate caffeine consumption can help you stay focused during those challenging reading assignments or while preparing for tests. It's like giving your brain a little pep talk!

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Cynthia Galinski, Helen Sing, Maria Thomas, and Gregory Belenky
INTRODUCTION

The demands and pace of continuous military operations produce sleep fragmentation and varying degrees of sleep deprivation in soldiers. The observable effects of this sleep disruption include decreased alertness, slowed thinking, lapses in attention, decreased motivation, and a performance phenomenon called the speed-accuracy-tradeoff. Several studies have documented performance and mood changes during periods of sleep deprivation (Babkoff et al., 1989a,b; Mikulincer et al., 1989; Thorne et al., 1983). There is a decline in the performance of accuracy tasks involving attention, reasoning abilities, and reaction time. Alertness decreases, and there are changes in self-reported fatigue (increases) and vigor (decreases). Sustaining optimum soldier performance relates to the prevention or amelioration of these changes. Three categories of solutions include the following: (1) Doctrinal solutions involve the overtraining of soldiers to perform their tasks with a minimum of cognitive effort; ensuring that soldiers are cross-trained so that crew members can substitute for each other when necessary; developing and adhering to appropriate work-rest cycles, including rotating crews as the mission permits; developing efficient leadership tactics so that unnecessary demands are not placed on subordinates; and modifying equipment and systems so that the likelihood of making errors is as small as possible. (2) Behavioral solutions make sure that soldiers sleep as much as they can, whenever they can (sleep discipline), while paying attention to where and how they sleep (sleep hygiene), that is, in as comfortable a position as possible, away from the noise and bustle of other soldiers and equipment. (3) Pharmacological solutions may be warranted in special circumstances, when adherence to doctrinal and behavioral solutions is not possible or breaks down. This last category of solutions for preventing or ameliorating sleep deprivation effects is the topic of the research reported in this chapter.

The characteristics of stimulant drugs useful in specific military situations are not only effectiveness but low therapeutic toxicity and low abuse potential, d-Amphetamine was tested for its ability to reverse changes in mood, alertness, and cognitive performance after an extended period of sleep deprivation (Newhouse et al., 1989). Although effective, its restricted legal status and the psychological side effects associated with long-term use, coupled with its abuse potential, almost certainly prohibit large-scale use. Caffeine is a universally available, legal, and socially accepted and used stimulant with low toxicity and low abuse potential. It is believed to reverse the performance and mood effects seen during sleep deprivation, although it has not been tested systematically.

Caffeine has a long history of use and can be found in many common foods, drinks, and medications. Although caffeine has been the subject of pharmacological studies for several decades, the mechanism of action of its effects on the central nervous system have only recently been defined as a blockade of adenosine receptors (Choi et al., 1988; Fredholm, 1985; Snyder, 1984). Extensive reviews of caffeine (Dews, 1984; Weiss and Laties, 1962) conclude that its stimulant properties are weak in comparison with those of other drugs (e.g., amphetamine) and that its effects are modest, making detection of these effects difficult and generalizations cumbersome. Dews (1984), however, states that the following three effects are clear: (1) it has the tendency to postpone sleep; (2) it reduces the degradation of performance because of fatigue and boredom; and (3) it decreases hand steadiness. The interpretation distilled from these and other reviews is that caffeine's effects are significant primarily when performance of repetitive, nonintellectual tasks is partially degraded. What is lacking in the literature and of importance to military operations is a systematic study of caffeine's effects on sleep-deprived individuals and the assessment of caffeine's effectiveness in reversing the changes caused by sleep deprivation.

EFFECTS OF CAFFEINE ON PERFORMANCE

A common method of assessing the effects of stimulant drugs is to measure individuals' reaction times on laboratory tasks. Older reviews and several recent articles failed to find that caffeine has significant effects on the reaction times of various tasks (Bruce et al., 1986; Kuznicki and Turner, 1986; Rapoport et al., 1981; Swift and Tiplady, 1988). Recently, however, caffeine has been found to significantly decrease reaction times in auditory and visual choice tasks when it was used at doses of as little as 32 mg and as great as 600 mg (Jacobson and Edgley, 1987; Lieberman et al., 1987a,b; Roache and Griffiths, 1987). Other cognitive and psychomotor skills measured by the digit-symbol substitution task, serial subtraction of numbers, addition, symbol cancellation, card sorting, signal detection, symbol copying, and number cancellation have not been found to be affected by caffeine (Bruce et al., 1986; Childs, 1978; Ghoneim et al., 1986; Lieberman et al., 1987b; Loke et al., 1985; Roache and Griffiths, 1987; Swift and Tiplady, 1988), although Battig et al. (1984) report that 300 mg of caffeine had a positive effect on a letter cancellation test.

EFFECTS OF CAFFEINE ON MOOD AND ALERTNESS

Several questionnaires and methods have been used to assess caffeine's effects on mood. Studies have shown that doses of 200 to 250 mg of caffeine elevate mood (Lieberman et al., 1987b; Swift and Tiplady, 1988) and that these effects can last for up to 3 h. Higher doses (600 mg) can produce increases in subjects self-ratings of tension or anxiety and increases in caffeine-related physical symptoms (Roache and Griffiths, 1987). Caffeine significantly affects measures of alertness and sleepiness. Doses of 100 mg and more postpone the onset of sleep (Dews, 1982; Goldstein et al., 1965), and a dose of approximately 300 mg significantly improves daytime alertness in both partially sleep-deprived and fully rested individuals, as measured by the multiple sleep latency test (Lumley et al., 1987). Walsh et al. (1990) report that 4 mg of caffeine per kg of body weight (approximately 300 mg) significantly increases latency to sleep onset at test periods throughout the night (0100 to 0500 h). This effect was seen in light and moderate caffeine users. Multiple sleep latency test results by Rosenthal et al., (1991) showed that caffeine at doses of 75 and 150 mg increases alertness whether an individual is fully rested or partially sleep deprived. Zwyghuizen-Doorenbos et al. (1990) showed that 250 mg of caffeine improved daytime alertness for at least 3 h in moderately sleepy subjects.

PHYSIOLOGICAL EFFECTS OF CAFFEINE

The literature supports the fact that caffeine has low toxicity and produces no serious physiological side effects in adults (Rall, 1985; Stavric, 1988). Caffeine's physiological effects are dependent on whether the subject is caffeine-naive or a regular user. In caffeine-naive subjects, a 250-mg oral dose increased the systolic blood pressure by 11 mm Hg (Robertson and Curatolo, 1984). The heart rate declined during the first hour after drug administration and then increased above the baseline during the second hour. Regular users who were deprived of caffeine showed a significant increase in their systolic blood pressure (4 mm Hg), whereas regular users who were not deprived of caffeine showed no significant increases. Other researchers have found no significant changes in blood pressure or heart rate even after a 500-mg oral dose (Bruce et al., 1986; Myers 1988). Newcombe et al. (1988) showed that doses of 300 to 350 mg do not affect the prevailing cardiac rhythm or rate and do not cause clinically significant ventricular or supraventricular dysrhythmias. Specific studies concerning the cardiovascular effects of caffeine at doses above 500 mg are lacking. In several studies, however, higher doses (up to 800 mg) were administered in other contexts (Chait and Griffiths, 1983; Griffiths and Woodson, 1988). Chait and Griffiths (1983) reported that one subject experienced shakiness and an upset stomach after receiving 200 mg of caffeine, and higher doses were not tested in that subject. All other subjects tolerated doses up to 800 mg well. Other clinically relevant physiological effects include the relaxation of smooth muscles (especially the bronchii) and diuresis. Respiration rate is increased by 250-mg doses in caffeine-naive users (Curatolo and Robertson, 1983). Caffeine has the ability to increase metabolic rate, but its effect on body temperature in humans has not been reported in the literature.

In summary, studies indicate that caffeine can have significant effects on mood and performance, even at relatively low doses, in non-sleep-deprived individuals and has effects on alertness in moderately sleep-deprived individuals. The following section reports the effectiveness of caffeine in reversing the alterations seen in performance, mood, and alertness following a prolonged period of sleep deprivation.

MATERIALS AND METHODS

Subjects

Fifty normal, healthy, nonsmoking, drug-free males between the ages of 18 and 32 (mean age, 23.6 years) were recruited through advertisements in college newspapers. Subjects were within normal weight limits for their height and were moderate users of caffeine (no more than 300 mg on a daily basis). After giving free and informed written consent, subjects underwent a thorough physical and laboratory examination and completed a self-assessment questionnaire for anxiety and depression (Snaith et al., 1976). Exclusion criteria included past or present major medical or psychiatric illness, positive urine drug screen, regular tobacco use, excessive caffeine use (more than 300 mg on a daily basis), questionnaire scores above 6 (out of a possible 12) for either anxiety or depression, or atypical sleeping patterns (e.g., self-reports of difficulty in falling asleep or regular involuntary early morning awakenings). Following completion of the screening procedures, the subjects were randomly assigned to one of four drug conditions: placebo ( n=12), 150 mg/70 kg ( n= 13), 300 mg/70 kg ( n=12), or 600 mg/70 kg ( n= 13).

Procedure

Subjects arrived in the laboratory in groups of three to four each on the evening before the sleep deprivation period began. All subjects were required to refrain from caffeine and alcohol ingestion for 72 h prior to the beginning of the study. Blood and urine samples were taken to ensure that the subjects were free of caffeine and other drugs of abuse. They were trained on a computerized performance assessment battery (Thorne et al., 1985) designed to assess several cognitive functions periodically at approximately 2-h intervals throughout the sleep deprivation period (see full description below). Eleven electrodes were attached to the scalp and face by using the international 10-20 system of electrode placement. Electroencephalograms (EEGs), electrooculograms (EOGs), and submental electromyograms (EMGs) were recorded continuously by using an 8-channel Oxford Medilog ambulatory cassette recorder. Dinner was provided between training sessions. Subjects retired at 2300 h. The sleep deprivation period began upon awakening the next morning at 0700 h (day 1). They remained awake for the next 64.5 h over a 3-day period (e.g., 0700 h Tuesday morning to 2230 h Thursday night), except for brief periods during administration of the modified Multiple Sleep Latency Tests (MSLTs). Subjects were monitored continuously by the staff to prevent unintentional sleep and were provided with books, games, movies, music tapes, conversation, and occasional brief walks to occupy them between tests.

On the morning of day 3 (at 0700 h after 48 h of sleep deprivation), a Teflon catheter was inserted into a forearm vein of each subject and was maintained with a heparin lock (heparin sodium, 20 Units/ml) to facilitate repeated drawing of blood samples before and after drug administration. At 0800 h (following 49 h of sleep deprivation), subjects were administered placebo or one of three doses of caffeine, USP anhydrous (City Chemical Corporation, New York, N.Y.). Doses were either 150, 300, or 600 mg/70 kg of body weight. Caffeine was administered orally by having the subjects drink 250 ml of an artificially sweetened lemon juice drink in which the caffeine powder was dissolved. Placebo consisted solely of the sweetened lemon juice drink. All doses were given in a double-blind manner.

Statistical Analysis

Separate two-factor repeated measures analysis of variance by using the General Linear Model (SAS Institute, Cary, N.C.) were performed for each dependent variable and POMS subscale. The two factors were group or dose and time. First, each dependent variable was analyzed for group differences and effects of the sleep deprivation period prior to the drug administration by using all measurements made prior to drug administration. Second, each dependent variable was analyzed for the effects of drug and time after drug administration by using the last value obtained prior to drug administration and all values obtained after drug administration. Statistical results thus reported for the main effects of drug dose, the main effects of time, and an interaction between these main effects. A level of P< 0.05 was accepted as significant, with the Greenhouse-Geisser adjustment criterion used in evaluating the main effects of time and the interaction between the main effects. Significant main effects were further evaluated by the Newman-Keuls Multiple Range Test.

RESULTS

Performance Tests

For each of the tasks, three measures of performance were analyzed: accuracy (percent correct), speed (responses per unit of time), and throughput (number of correct responses per unit of time). The throughput measure takes both accuracy and speed of performance into account and was subjected to statistical testing. Significant effects of caffeine were observed on the throughput measure for the choice reaction time, serial addition/subtraction, and logical reasoning tasks ( Figure 20-1 and Table 20-1).

Performance on the choice reaction time task for 8 h after drug administration in subjects who received the 600-mg dose was significantly different from that in subjects who received the placebo. The 150-mg dose improved performance for 4 h. For subjects receiving the 300-mg dose, performance was not significantly different from that for subjects receiving the placebo at any point following administration. For the serial addition/subtraction task, all doses of caffeine significantly improved performance for 3 h. For subjects receiving the 600-mg dose, performance remained significantly better than that for subjects receiving placebo for 10 h after drug administration, with no significant differences observed among the dose groups at the final 12-h testing period. Performance on the logical reasoning task by subjects receiving the two highest doses of caffeine was significantly better than by subjects receiving placebo for the entire 12-h period. In addition, caffeine restored performance to the levels obtained after rest during this interval. Performance after administration of the 150-mg dose was significantly different from that after administration of placebo for 6 h after drug administration.

Mood Measures

The effects of sleep deprivation on mood, as measured by the POMS and VAS, are reported in more detail elsewhere (Penetar et al., 1993). Briefly, the scores of all six subscales of the POMS changed significantly as a result of the sleep deprivation. Tension [F(5,230)=12.3, P<0.001], anger [F(5,230)= 7.42, P<0.001], depression [F(5,230)=16.4, P<0.001], fatigue [F(5,230) =97.9, P<0.001], and confusion [F(5,230)=57.4, P<0.001] increased, whereas vigor decreased [F(5,230)=87.3, P<0.001]. Similarly, ratings on the VAS showed the effects of sleep deprivation. The main effects for the time before drug administration showed that alertness [F(4,184)=103.39, P< 0.001], energy levels [F(4,184)=109.2, P<0.001], confidence [F(4,184)= 48.96, P<0.001], and talkativeness [F(4,184)=23.46, P<0.001] declined, whereas irritability [F(4,184)=20.29, P<0.001] and sleepiness [F(4,184)= 138.11, P<0.001] increased.

Following caffeine administration, significant increases in the POMS vigor subscale and significant decreases in the POMS subscales of fatigue and confusion were observed ( Table 20-1). Vigor ratings for all three dose groups were significantly different from those for the placebo group for 2 h after caffeine adminstration. Vigor ratings for the 600-mg dose group were 97 percent of those for subjects in the rested condition 1 h after caffeine administration and remained at 84 percent of those for subjects in the rested condition at the 2-h measurement. Conversely, fatigue ratings for all three caffeine dose groups decreased significantly for 2 h following caffeine administration. Confusion ratings in the 150-mg dose group were significantly decreased in comparison with those in the placebo group 2 h after caffeine administration.

Caffeine reversed the sleep deprivation effects reported in subjective ratings of alertness for 2 h, energy levels for 12 h, confidence for 2 h, sleepiness for 12 h, and talkativeness for 2 h following drug administration. Caffeine significantly increased self-rated anxiety for 2 h, and jitteriness or nervousness for 12 h following drug administration. Ratings of heart pounding, headache, sweatiness, and upset stomach were unaffected by caffeine.

Alertness Measures

Vital Signs

Diastolic blood pressure and oral temperature were significantly affected by caffeine administration ( Table 20-1 and Figure 20-3). At 1 h after admini stration, both the 300- and the 600-mg doses significantly increased diastolic blood pressure in comparison with the placebo; there were no significant differences at other time points. The 600-mg dose of caffeine significantly increased oral temperature in comparison with placebo at several measurement times after administration: 2, 2.5, 3, 4, 6, 8, and 12 h. Neither systolic blood pressure nor pulse was significantly affected.

DISCUSSION

The study described here indicates that caffeine is effective in reversing the performance degradations and the alterations in mood and alertness produced by periods of prolonged sleep deprivation. The results indicate that these beneficial effects can be long-lasting and not at the expense of serious mood or physiological side effects.

Sleep deprivation degrades cognitive performance. The effects of caffeine on performance in non-sleep-deprived volunteers have been well documented, even at the low dose levels commonly found in food and drink products (see Lieberman [1992] for a review). The study described here extends the usefulness of caffeine, showing that large doses (up to 600 mg) are effective in improving a variety of cognitive performances in sleep-deprived individuals, and outlines the time course of its effects in these individuals. The tasks used in the present study were chosen to sample a variety of cognitive abilities with varying mental demands. Choice reaction time requires little thinking but does require great accuracy and speed. The serial addition/subtraction task is a machine-paced task but has a greater mental component, whereas the logical reasoning task is self-paced and requires the greatest amount of thought for accurate responses. Caffeine produced improved performances of all three tasks, with performance returning to those of rested subjects for up to 12 h after caffeine administration. Caffeine was not observed to affect recall or code substitution tasks. In toto, these results are in concert with those presented previously (Lieberman, 1992; Roache and Griffiths, 1987) and document for the first time the relatively long-lasting effects of this drug on cognitive performance. The study described here shows that caffeine compares favorably with amphetamine in reversing the effects of sleep deprivation on cognitive performance. Using an identical sleep deprivation paradigm, Newhouse et al. (1989) showed that 20 mg of amphetamine is required to produce sustained performance improvements.

Sleep deprivation also alters mood and degrades alertness. The present study documents the fact that caffeine can have significant beneficial effects in reversing these mood changes; sleepiness and confusion declined, whereas increases in energy and confidence levels were reported. Although there were increased ratings of anxiety and jitteriness or nervousness, these effects were not severe and did not elicit complaints from the subjects. Depending on the measure, alertness, which was severely degraded by 49 h of sleep deprivation, was improved for 2 to 4.5 h, whereas self-ratings of sleepiness in groups treated with caffeine remained significantly lower than those in the placebo group for 12 h. In this regard, caffeine was not as effective as amphetamine. The alertness of amphetamine treated subjects (20 mg), as measured by sleep latency tests, was nearly restored to the levels of rested subjects for 7 h (Newhouse et al., 1989). Caffeine's effects on alertness are therefore less potent and shorter acting than amphetamine's.

Caffeine's effects on physiological measures are important for assessing its usefulness as a stimulant. The study described here shows that relatively high doses of caffeine are well tolerated by sleep-deprived individuals and that its effects are similar to those found in other studies in non-sleep-deprived subjects given lower doses than those used in the present study (Myers, 1988; Newcombe et al., 1988). Additionally, there were no changes in self-reports of other side-effects (heart pounding, headache, sweatiness, upset stomach). Of note was caffeine's observed effect on oral temperature. Oral temperature normally rises during the day, from a low in the early morning hours to a peak in the early evening hours. The subjects in the present study showed this typical response. Caffeine increased temperatures above the normal rise throughout the observation period, again revealing an important aspect of its effects and duration of action. The significance of this effect awaits further experimentation, although this type of effect has been observed previously with another stimulant, d-amphetamine (Newhouse et al., 1989).

RECOMMENDATIONS

The results of the present study would seem to indicate that caffeine can be an ideal stimulant for use during military operations when performance declines secondary to sleep disruption and sleep fragmentation. Doses of 600 mg are needed to reverse severely degraded performance as a result of long periods of sleep deprivation. Presumably, lower doses (200-400 mg) would be effective in ameliorating the changes caused by shorter periods of deprivation.

Given the legal and social acceptance of caffeine, and its low abuse potential, caffeine tablets (200 mg/tablet) should be included in food rations.

Use of caffeine should be restricted to special situations when sleep has been unusually disrupted and for the benefit of temporarily (10-12 h) restoring alertness and sustaining performance during critical periods of military operations.

Finally, although caffeine can temporarily sustain performance during continuous operations, it should be emphasized that no drug can substitute for adequate sleep.

ACKNOWLEDGMENTS

The authors thank the staff of the Behavioral Biology, in particular Sharon Balwinski and Kevin Peyton, for assistance in the conduct of the experiment described here. Investigators adhered to AR 70-25 and USAMRDC Reg 70-25 on the use of volunteers in research. Use of trade names does not constitute endorsement of product. The views of the authors do not purport to reflect the position of the Department of the Army or the Department of Defense.

REFERENCES

AR 70-25 1989. See U.S. Department of the Army. 1989.

Bruce, M., N.Scott, M.Lader, and V.Marks 1986. The psychopharmacological and electrophysiological effects of single doses of caffeine in healthy human subjects. Br. J. Clin. Pharmacol. 22:81-87. [ PMC free article: PMC1401080 ] [ PubMed: 3741730 ]

Eddington, N.D., S.I.Lugo, G.Kamimori, E.Fadiran, D.Penetar 1993. The influence of caffeine administration on in-vivo catecholamine pharmacodynamics in sleep deprived volunteers. Pharmacol. Res., 10:S-360.

McNair, D.M., M.Lorr, and L.F.Droppleman 1981. Profile of Mood States. San Diego, Calif: Educational and Industrial Testing Service.

Newhouse, P.A., G.Belenky, M.Thomas, D.Thorne, H.C.Sing, and J.Fertig 1989. The effects of d-amphetamine on arousal, cognition, and mood after prolonged total sleep deprivation. Neuropsychopharmacology 2:153-164. [ PubMed: 2742729 ]

U.S. Department of the Army. 1989. Army Regulation 70-25. "Use of Volunters As Subjects of Research". 25 October. Washington, D.C..

Wever, R. 1979. The Circadian System of Man. Berlin: Springer-Verlag.

DISCUSSION

HARRIS LIEBERMAN: We have some unpublished data from a couple of studies in which we did find significant effects of caffeine on mood swing. We did not use doses as low as 32 milligrams but used doses of 64 and 128 milligrams of caffeine. Effects on performance by doses lower than those are hard to detect, but over the long run, over a series of studies, my feeling is that there really are effects with low dosages, and those are the doses that we typically take in our background.

JOEL GRINKER: I was just curious whether in any of the caffeine studies or in any of the other supplement studies age has been looked at systematically as a factor. I have two thoughts, one, that in fact it might potentiate the ability of older individuals or that in fact it has less effectiveness, and I wonder if you have any comments.

DAVID PENETAR: I have here one study that related to age. Typically, these studies were done, with young, healthy males.

HARRIS LIEBERMAN: We did look at the age parameter in one of our caffeine studies, but we did not see any significant differences as a function of age or gender.

JOHN VANDERVEEN: I was curious as to the uniformity of the synthesis associated with sleep. Do you find much variation that would indicate that shortness of sleep time versus onset of sleep, etc. Are they uniform in your subjects or are they highly individualistic?

DAVID PENETAR: In terms of a rested individual?

JOHN VANDERVEEN: Yes.

DAVID PENETAR: What we do is we bring them into the study the night before and give them 9 hours of time in bed before we start the study, so at that time they are all pretty consistent in the amount of sleep that they have had.

JOHN VANDERVEEN: No, I meant the effects of caffeine on their subsequent sleep. Do you find a uniform effect in terms of delay of sleep or shortness of length of sleep, etc?

DAVID PENETAR: We did not specifically look at that because by the time they went to bed it was over 12 hours after they had received caffeine.

WILLIAM WATERS: A couple of questions. One pertaining to the onset of parameters. Did you have a look at whether or not you have any data or whether or not sleep can be induced prior to that?

DAVID PENETAR: No, I do not have any data on that. I am not sure that is reported.

WILLIAM WATERS: It could be that what you had was a referral of something that might allow it to occur. The other thing was, under the influence of caffeine, did you notice any change in the number, the length, stage one, and arousals?

DAVID PENETAR: Again, by the time our subjects went to bed, it was over 12 hours after they had received the caffeine, and we did not see any changes; there were no differences between the groups. We did monitor them. We recorded them through their sleep, and we saw no differences in sleep architecture, time of sleep, time to bed, or sleep efficiency; we saw no differences for 12 hours.

JOHANNA DWYER: I worked with a neurologist who was interested by some observations years ago, when they did a lot more electroconvulsive shock than they do now. Apparently, they used to prime the patients with caffeine, and by doing this, they could use a lower level of shock and still get the same effect. The reason I bring it up here is not because I hope anyone here is heavily into this, but rather, are there other changes in the electroencephalograms in terms of caffeine's effects that may be in addition to what we have been talking about?

DAVID PENETAR: No, I do not know.

ALLISON YATES: Just one thing. I noticed in some of the graphs that it almost looked as if at 600 milligrams the subjects might have had even a little bit better performance than they had initially in their first 24 hours. This result is important in considering enhancement of performance with normal subjects.

DAVID PENETAR: Harris, your subjects could not sleep at night.

HARRIS LIEBERMAN: Yes, two slides that you showed with my studies, the vigilance and reaction times, were for subjects who had stayed up all night the night before and who were back in the morning after the administration. Their performances were similar to those with placebos under the same conditions. I consider that to be above normal, although since caffeine is such a common component of the diet, it is hard to untangle it all.

ALLISON YATES: That is why I was wondering yesterday what the baseline levels were.

HARRIS LIEBERMAN: We typically include that as a parameter in our studies and look to see whether there are differences between moderate, low, and heavy caffeine users in their responsiveness, and in the low and moderate range there is not much difference. When you get to the real high users, you see big differences in responsiveness. That depends on the timing of administration, whether they are in a deprivation stage, or whether they are already on a lot caffeine.

ROBERT NESHEIM: Were you defining it high?

HARRIS LIEBERMAN: Average caffeine consumption is about 200 milligrams per day, which is maybe three cups of not very strong coffee. I define high for the purpose of categorizing subjects as above 400 or 500 milligrams per day.

DAVID SCHNAKENBERG: Just a couple of observations. We used to always think that members of the Army must be heavy coffee drinkers because you get that perception, but looking out in field studies where soldiers are eating rations, we found out that even though you gave a meal ready-to-eat, 90 percent of the coffee packets were returned unused. The rest of the 10 percent probably went mostly to the senior sergeants, who had a chance to stay by the talking place and make some coffee for themselves. So young soldiers in the field today are not heavy coffee drinkers. I am sure they drink plenty of caffeine if they have carbonated beverages. But most of the time carbonated beverages are not available to them in the field, although maybe in Desert Storm cans of Coke manged to get inside of the tanks anyway.

My question is, has anybody done sleep studies on evaluating caffeine using the vehicle of delivering the caffeine in the form of a cola or in the form of a coffee beverage itself?

DAVID PENETAR: A number of studies look at coffee drinking when they give caffeine. In fact, in some of the studies reported here, they took decaffeinated coffee and added caffeine to it, and the subjects drank it that way. In other studies it was either caffeine pills or caffeine powder dissolved in some drink.

DAVID SCHNAKENBERG: Can subjects get a comparable effect with the caffeinated coffee versus decaffeinated coffee? For instance, I am sure your subjects knew when they were receiving a placebo.

DAVID PENETAR: Ours was powdered caffeine dissolved in a lemon juice drink, and the lemon juice drink was very bitter. As you know, caffeine powders are very bitter, so they could not tell what they were drinking other than lemon juice drink. If they talked among themselves, they just said "oh, it is not very good, it was bitter."

WILLIAM BEISEL: So many of the emergency rations and so on seem to be candy bars with chocolate flavoring. How much of that is caffeine?

DAVID PENETAR: Milk chocolate has about 7 milligrams per ounce, whereas bakery chocolate or unsweetened chocolate has about 35 milligrams per ounce. They figure that, for example, a Hershey's candy bar has 25 to 35 milligrams per ounce, so it is not a lot, and it is less than most sodas.

1

David M.Penetar, Walter Reed Army Institute of Research, Washington, D.C. 20307-5100

1

Subjects were paid for their participation. The investigators adhered to AR 70-25 (U.S. Department of the Army, 1989) and U.S. Army Medical Research and Development Command Reg 70-25 (1989), on the use of volunteers in research.

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Effects of Caffeine on Cognitive Performance, Mood, and Alertness in Sleep-Deprived Humans

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David M.Penetar, 1 1David M.Penetar, Walter Reed Army Institute of Research, Washington, D.C. 20307-5100 Una McCann,

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Previous research suggests that effects of caffeine on behaviour are positive unless one is investigating sensitive groups or ingestion of large amounts. Children are a potentially sensitive subgroup, and especially so considering the high levels of…

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Using Caffeine to Optimize Mental & Physical Performance | Huberman Lab Podcast 101

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Moderate caffeine consumption increases alertness and reaction time, improves memory and cognitive skills, and improves mood. In a conducted by the National Institute of Aging, part of the U.S. Department of Health and Human Services, participants who were given caffeine before a cognitive test scored higher than those who had no caffeine. Beyond that, suggest that the benefits of caffeine include helping to prevent Parkinson's disease, reducing the risk of gallstones, preventing weight gain and even stimulating hair growth .

Long-term caffeine use has been found to increase the risk of certain kinds of heart disease, such as coronary heart disease and hypertension, but seems to lower the risk of other types of fatal heart diseases. More common risks of caffeine consumption above the recommended amounts include insomnia, a fast heartbeat, restlessness, and muscle tremors. A showed that caffeine increases the effects of nicotine on the body, which means that smokers who consume caffeine may form stronger nicotine addiction.

Consuming moderate amounts of caffeine does not appear to be harmful, and may even be beneficial, but it's not without risk. Will you give up caffeine?

More Resources

Video: SciShow

Learn about the effects of caffeine on the body.

Article: National Academic Press
6 Caffeine Effects
Read about the effects of caffeine on various aspects of human behavior.

Website: Business Insider
Caffeine Consumption by Age
See how caffeine consumption compares by age and source.

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For many people, caffeine jump starts the day. But does it have health benefits or health risks? How much caffeine do you consume? Join the conversation.

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Caffeine is a stimulant and the most commonly used drug in the world. Every day, millions consume it to increase wakefulness, alleviate fatigue, and improve concentration and focus.

Amid myths and controversy about whether caffeine is good or bad for us, evidence suggests that moderate coffee consumption can bring both benefits and risks.

However, a high consumption of caffeine may not be healthful. In addition, the recent trend of adding caffeine to drinks and snacks that do not naturally contain it has raised new concerns.

This article will look at the potential health benefits and risks of caffeine, the questions of energy drinks, and the likelihood of a caffeine overdose occurring.

The Food and Drug Administration (FDA) consider caffeine to be both a drug and a food additive. They recommend a maximum intake of 400 mg a day.

In prescription and over-the-counter (OTC) medicines, caffeine is used to treat tiredness and drowsiness, and to improve the effect of some pain relievers.

It belongs to a group of medicines called central nervous system (CNS) stimulants.

Foods containing caffeine can help restore mental alertness.

Caffeine's use as an alertness aid should only be occasional. It is not intended to replace sleep and should not regularly be used for this purpose.

In the United States (U.S.), more than 90 percent of adults use caffeine regularly, with an average consumption of more than 200 milligrams of caffeine per day. This is more caffeine than in two 6-ounce cups of coffee or five 12-ounce cans of soft drink.

Caffeine occurs naturally in the leaves, seeds, or fruit of more than 60 plant species, including:

coffee beans

tea leaves and buds

dola nuts

cacao beans

guarana seeds

yerba mate leaf

Caffeine in plants acts as a natural pesticide. It paralyzes and kills insects that attempt to feed on them.

Food sources

Caffeine features in tea, coffee, and chocolate, and it is regularly added to gum, jelly beans, waffles, water, syrup, marshmallows, sunflower seeds, and other snacks.

The FDA recommends that healthy adults limit their caffeine intake to a maximum of 400 milligrams (mg) a day, about 4 or 5 cups of coffee. This amount is not associated with negative effects.

There is no set limit for children, but the American Academy of Pediatrics (AAP) discourages the consumption of caffeine and other stimulants by children and adolescents.

The amount of caffeine included in some common foods and beverages are:

One 8-ounce cup of coffee: 95 to 200 mg

One 12-ounce can of cola: 35 to 45 mg

One 8-ounce energy drink: 70 to 150 mg

One 8-ounce cup of tea: 14 to 60 mg

Decaffeinated cola and soft drinks contain no caffeine, but decaffeinated coffee is not caffeine-free.

"Energy drinks" contain varying amounts of caffeine.

Additional products are now appearing on the market, from "psyched up" oatmeal to "wired" waffles.

These have raised concerns, especially regarding the potential impact on children and adolescents. The FDA has questioned the safety of this practice.

Caffeine may have some health benefits, but not all of these have been confirmed by research.

Weight loss

Caffeine may boost weight loss or prevent weight gain, possibly by:

suppressing the appetite and temporarily reducing the desire to eat

stimulating thermogenesis, so the body generates more heat and energy from digesting food

Weight loss products that are marketed as thermogenics may contain caffeine and ephedra, or ephedrine.

Research has not confirmed long-term results.

Alertness

A 75-mg serving of caffeine can increase attention and alertness, and a 160 to 600-mg dose may improve mental alertness, speed reasoning, and memory.

However, caffeine is not a substitute for sleep.

Sports performance

Caffeine can improve physical performance during endurance exercise.

The European Food Safety Agency (EFSA) recognize that caffeine can increase endurance performance, endurance capacity, and reduction in perceived exertion.

However, the effects on short-term, high-intensity exercise remain inconclusive.

Brain function

Caffeine affects adenosine receptors in the brain. Coffee also contains polyphenol antioxidants, and these, too, act on various pathways.

Studies have suggested that drinking coffee may help enhance some thinking skills and slow the mental decline that comes with age.

However, more research is needed to confirm this.

Alzheimer's and Parkinson's disease

Research has found that lifelong caffeine consumption may reduce the risk of developing Alzheimer's disease.

Studies have also reported that people with a higher coffee consumption have a lower risk of Parkinson's disease.

Memory

Research from Johns Hopkins University suggests that a dose of caffeine after a learning session may help boost long-term memory.

Liver and colon

It has been suggested that caffeine enemas may help prepare the colon for an endoscopy or colonoscopy by supporting the excretion of bile through the colon wall.

Proponents claim that a caffeine enema increases the levels of glutathione, an antioxidant, and so it supports the natural processes of detoxification in the liver.

However, there is little evidence to support this theory.

Coffee consumption may help decrease the risk of cirrhosis and slow the rate of disease progression in hepatitis C infection. Observational studies have found that coffee may have protective benefits for people with hepatocellular cancer.

Eyelid spasm

There is some evidence that caffeine may help protect people from an eye disorder known as blepharospasm.

This condition, caused by abnormal brain function, makes people blink incessantly and can leave them functionally blind.

Cataracts

Researchers have found that caffeine may help protect the lens of the eye against damage that could lead to the formation of cataracts.

Skin cancer

Some scientists have suggested that caffeine may guard against certain skin cancers.

One team found that caffeine applied directly to the skin of mice helped prevent damaging ultraviolet (UV) light from causing skin cancer.

Others have linked the consumption of three cups of caffeinated coffee a day with a 21 percent lower risk of developing basal cell carcinoma in women, and a 10 percent lower risk in men, compared with drinking less than one cup per month.

Kidney stones

A study of 217,883 participants analyzed the association between caffeine intake and the risk of developing kidney stones.

Those who consumed more caffeine had a lower risk of developing kidney stones.

Mouth, throat, and other cancers

In a study of 968,432 men and women, participants who drank than 4 cups of coffee a day had a 49-percent lower risk of death from oral cancer, compared with those who drank no coffee at all or only an occasional cup.

Other possible cancer-related benefits include:

a lower risk of endometrial cancer

a reduced risk of prostate cancer

protection against head and neck cancer

protection against the recurrence of breast cancer

Stroke

Data for 34,670 women in Sweden without a history of cardiovascular disease indicated that women who drank more than one cup of coffee per day had a 22 to 25-percent lower risk of stroke compared with women who drank less.

Low or no coffee drinking appeared to be linked to an increased risk of stroke.

Type 2 diabetes

One longitudinal study found that participants who increased their coffee intake by more than one cup a day over a 4-year period had a 1 percent lower risk of developing type 2 diabetes compared with people who did not change their intake.

People who lowered their daily consumption by more than one cup of coffee showed a 17 percent higher risk for type 2 diabetes.

A study published in Diabetes Care in 2004 linked a high coffee consumption over a period of 4 weeks with increased fasting insulin concentrations.

However, the reasons for the link were unclear. It may be due to lowered insulin sensitivity, meaning the body does not use the insulin produced efficiently.

The team called for more investigation before asserting that high coffee consumption lowers risk for type 2 diabetes.

Much of the published research about caffeine suggests that it is beneficial, in moderation.

However, some studies highlight the potentially harmful effects of caffeine.

Depression

A high caffeine intake may worsen symptoms of anxiety and depression.

Research published in 2016 found that, in 234 middle school students in Korea, a higher caffeine intake was linked to higher weight, lower academic achievement, and a higher risk of severe depression.

However, whether the caffeine leads to depression or depression causes people to consume more caffeine remains unclear.

Blood sugar

People with type 2 diabetes report that their blood glucose levels rise after consuming caffeine.

There is some evidence that caffeine may impair insulin action, leading to a small but detectable rise in blood sugar levels, particularly after meals.

Pregnancy

Studies have suggested that more than 300 mg a day of caffeine, or the amount equal to around three cups of coffee, could lead to:

loss of pregnancy

delayed fetal growth

abnormal fetal heart rhythm

According to the National Institutes of Health (NIH), the weeks before pregnancy also count. Research shows that if both parents consume more than two caffeinated drinks a day in the weeks before they conceive, a loss of pregnancy may be more likely.

Women should limit their caffeine intake to 200 mg or less during pregnancy.

Fertility

Some research suggests that caffeine may reduce muscle activity in the fallopian tubes, which carry eggs from the ovaries to the womb.

This could mean, say the study authors, that caffeine reduces a woman's chances of becoming pregnant by about 27 percent.

Breast-feeding

Caffeine passes into breast milk in small amounts, and it may build up in the nursing infant.

Infants whose mothers drink large amounts of caffeinated beverages may be jittery and have trouble sleeping.

Gout

An additional intake of caffeine may trigger a gout attack in people with the condition.

Drinking six or more caffeinated beverages in 24 hours has been associated with an almost four-fold increase in the risk of recurrent gout attacks.

Incontinence

A study that looked at 1,356 women found that those with an intake of 329 mg of caffeine a day, equivalent to about three cups of coffee or more, had a 70-percent higher chance of bladder problems.

Insomnia

Consuming caffeine 3 and even 6 hours before bedtime can significantly disrupt sleep. Up to 6 hours before bedtime, caffeine can reduce objectively measured total sleep time by more than 1 hour.

Headaches

A population-based study found that dietary and medicinal caffeine consumption may be a modest risk factor for triggering chronic daily headache, regardless of headache type.

Menopause

A study published in the journal Menopause found that women who consumed caffeine during menopause were more likely to have hot flashes and night sweats.

Other adverse effects

Caffeine's main effect on the body is an increased temporary sense of wakefulness and alertness, but it can also cause uncomfortable symptoms.

Consuming over 400 mg of caffeine a day can lead to:

Caffeine increases the release of acid in the stomach, sometimes leading to an upset stomach or heartburn.

Caffeine can interfere with the sleep cycle. Sleep loss is cumulative, and even small nightly decreases can add up and disturb daytime alertness and performance.

Drug interactions

Some medicines may interact with caffeine.

These include some:

Antibiotics

Bronchodilators

Antipsychotics, such as clozapine

Some antidepressants

Carbamazepine, as caffeine could increase the risk of seizures

Caffeine may also interact with diuretics, estrogens, valproate, and some other medications.

A number of herbs and supplements can interact with caffeine to varying degrees:

A number of myths surround caffeine consumption. Have a look at some of them.

1. Is caffeine addictive?

In 2013, the American Psychiatric Association (APA) added caffeine withdrawal to the list of recognized conditions in the Diagnostic and Statistical Manual of Mental Disorders (DSM-V). However, not all caffeine consumers have withdrawal symptoms if they stop consuming caffeine.

People who suddenly stop drinking coffee may experience symptoms about 12 to 24 hours after quitting. These peak after 20 to 48 hours before disappearing. Gradually reducing caffeine intake over a period of days does not trigger these symptoms.

Unlike other drugs, caffeine has not been shown to activate the pathways in the brain that are related to addiction.

Therefore, caffeine is not considered an addictive substance.

2. Is caffeine a diuretic?

Caffeine has been associated with increased urinary volume and frequency, causing the body to lose water and electrolytes such as potassium and sodium.

However, researchers have not found a significant difference in fluid loss between people who drink or do not drink coffee.

One team concluded that: "Coffee, when consumed in moderation by caffeine habituated males provides similar hydrating qualities to water."

Additional water loss may occur if a person consumes more than 250 mg a day, but the fluid consumed with the drink is likely to make up for any loss.

3. Does coffee cause osteoporosis?

Caffeine may affect the way the body absorbs calcium, and this has raised concerns that drinking coffee can lead to osteoporosis.

However, this has not been confirmed by research.

A Swedish study of data for over 60,000 women found that: "High coffee consumption was associated with a small reduction in bone density that did not translate into an increased risk of fracture."

Women with a good intake of calcium through their diet are unlikely to be at risk of osteoporosis as a result of drinking coffee.

4. Does caffeine sober you up?

People who have drunk too much alcohol often turn to coffee or an energy drink to sober them up.
However, caffeine does not sober a person up or make them fit to drive. It may make them more alert, but it does not reverse the poor judgment and other effects associated with alcohol.
In fact, it could be more dangerous because, without the drowsiness, a person is more likely to believe they are sober, which could lead to hazardous activities such as driving home or consuming more alcohol.

The caffeine and sugar content in energy drinks could be detrimental to health.

There is some controversy around energy drinks. They have been banned from a number of student campuses, because of reports of health problems and even fatalities.

The amount of caffeine in an energy drink depends on the brand and type.

While one 16-ounce Americano coffee can contain 225 mg of caffeine, the caffeine content of a 16-ounce can of energy drink until recently ranged from 160 mg to 357 mg.

Producers of the drink that contained 357 mg of caffeine have now lowered their caffeine content to 300 mg. It carries a health warning that it should not be consumed by children, those with heart problems, or those who may have an intolerance to caffeine.

Energy drinks contain not only caffeine but other plant-based stimulants, simple sugars or artificial sweeteners, and additives. A 16-ounce serving of one well-known energy drink would contain around 50 g, or 1.75 ounces, or 5 teaspoons of sugar.

These high concentrations of caffeine and sugar could have a negative impact on the body.

Mixing alcohol and energy drinks

When alcoholic beverages are mixed with energy drinks, the caffeine can mask the depressant effects of alcohol. Alcohol also decreases the metabolism of caffeine, prolonging its effects.
Drinkers who consume alcohol mixed with energy drinks are three times more likely to binge drink than drinkers who do not report mixing alcohol with energy drinks.
They are also twice as likely to report experiencing sexual assault, sexually assaulting someone else, riding with a driver who was under the influence of alcohol, being physically hurt or injured, and requiring medical treatment.

A person is unlikely to die from consuming too much caffeine in the diet. It is estimated that it would take 149 or so cans of caffeinated energy drink to kill an average adult male. Vomiting would most certainly occur before a person had a chance to consume a fatal overdose of caffeine from dietary sources.

Caffeine pills are popular with young people, but they can be hazardous.

However, pure caffeine is a powerful stimulant, and very small amounts can lead to an accidental overdose. A single teaspoon of pure caffeine is roughly equivalent to 28 cups of coffee.

In addition to the usual adverse effects from too much caffeine, high doses can lead to:

anxiety

heart palpitations and rapid heart beat

sweating

nausea and vomiting

cardiac arrest

Following the deaths of at two young men from an overdose of pure caffeine sold over the internet, the FDA urges people "to avoid pure, powdered caffeine." They also call on parents to be aware that these products may attract young people.

Whether consumed as a food or a medicine, the blood and body tissues absorb caffeine within around 45 minutes. It reaches peak level in the blood within 1 hour and remains there for 4 to 6 hours.

While there, caffeine changes the way the brain and body work.

Caffeine has a similar structure to adenosine, a chemical that is present in all human cells.

In the brain, adenosine acts as a CNS depressant.

Adenosine promotes sleep and suppresses arousal by slowing down nerve activity. Adenosine binding also causes blood vessels in the brain to dilate, to increase oxygen intake during sleep. When awake, the levels of adenosine in the brain rise each hour, making the brain and the body less alert.

To a nerve cell, caffeine looks like adenosine, and caffeine binds to the adenosine receptors.

However, unlike adenosine, it does not decrease the cell's activity. As caffeine utilizes all the receptors adenosine binds to, the cells can no longer sense adenosine. As a result, instead of slowing down because of the adenosine level, cellular activity speeds up.

Caffeine blocks adenosine's ability to open up the brain's blood vessels, causing them to constrict. This is why caffeine is used in pain relief medicine for headaches. If the headache is vascular, relief comes as the caffeine narrows the blood vessels.

The blocking of adenosine causes excitatory neurotransmitters to increase in the brain. The pituitary gland notices this increased activity and releases hormones that tell the adrenal glands to produce epinephrine.

Moderate amounts of caffeine appear not to be harmful, and a moderate intake of caffeine may bring health benefits.

The FDA recommends an intake of no more than 400 mg a day.

However, the impact will vary according to the amount consumed, the individual's size, sex, and sensitivity to the effects, and any medications or supplements they may be taking.

Pure caffeine can be dangerous, even life-threatening, and should be avoided.

In addition, the current trend for adding caffeine to foods such as gum and ice cream, items that commonly target children remains a matter of concern, and investigations are ongoing.

Anyone wishing to give up caffeine should cut down over a few days rather than at once, to avoid uncomfortable symptoms.

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Caffeine is a stimulant that occurs naturally in several foods. Some companies also add it artificially to their drinks and snacks. In small doses it can improve alertness. The FDA recommends no more than 400 mg a day as too much may negatively impact health. Find out more about caffeine's benefits and risks here.

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Many people can't imagine starting their day without a cup of coffee or tea. Caffeine has become the silent hero fueling our daily lives, helping people get through that afternoon slump. It can also have positive effects on alertness, cognitive function and athletic function. But as we indulge in our favorite caffeinated beverages, there are also some concerns about excessive consumption and potential health risks.

Caffeine is a chemical stimulant that can be found naturally in coffee beans, tea leaves, cacao beans, guarana berries and yerba mate leaves and quickly boosts alertness and energy levels. It can also be made synthetically and added to drinks, food, tablets and supplements.

The AMA's What Doctors Wish Patients Knew ™ series provides physicians with a platform to share what they want patients to understand about today's health care headlines.

In this installment, four AMA members shared what doctors wish patients knew about caffeine. They are:

Nicole Clark, MD, a neurologist in Helena, Montana, and an AMA delegate for the Montana Medical Association.

Stephen Devries, MD, a preventive cardiologist and executive director of the educational nonprofit Gaples Institute in Chicago.

Nerissa Fernandes, DO, an internist at Rush University Medical Center, which is part of Chicago's Rush University System for Health.

Shannon Kilgore, MD, a neurologist in Palo Alto, California. She is also an AMA delegate for the American Academy of Neurology.

Rush University System for Health is part of the AMA Health System Member Program, which provides enterprise solutions to equip leadership, physicians and care teams with resources to help drive the future of medicine.

Pay attention to consumption

About 85% of adults consume 135 milligrams of caffeine daily in the U.S. This is equivalent to 12 ounces of coffee, which is the most common source of caffeine for adults.

The amount of caffeine in brewed coffee "can vary greatly depending on the type of bean, the amount of grind, the size of the particles, the brew time and other factors pertaining to the source," said Dr. Kilgore. "And then, of course, tea and soft drinks tend to have less caffeine."

"The Food and Drug Administration considers less than 400 milligrams of caffeine per day as safe," said Dr. Fernandes, which "is about two to three 12-ounce cups of coffee a day."

"Of course, if you're getting jittery, it's too much caffeine," said Dr. Clark.

Additionally, "per the American Academy of Pediatrics, in general, young kids should avoid caffeine," said Dr. Fernandes.

Try small, frequent doses

"One of the things that people don't realize is, if you think of it as a medicine, then the best way to use it is in small, frequent doses," said Dr. Kilgore. "So, 20 milligrams to 100 milligrams at a time as opposed to the standard American mug of coffee.

"And then just getting it into your brain a small amount at a time," she added, noting that "if you're home with the increase of telework and things like that it might be easy to just serve yourself a little bit at a time throughout the day."

"Then, when you start to feel your mental performance lagging, take it a little bit more-up until 2 p.m.," Dr. Kilgore said.

BP and heart rate can rise

"With regards to heart health, blood pressure and heart rate can be raised by caffeine intake," said Dr. Fernandes. "I ask patients not to drink caffeine about 60 minutes prior to their appointment, especially if I'm monitoring or treating them for high blood pressure."

Caffeine "can also cause an increase in heart rate, as well as causing some extra heartbeats," she said. "Not necessarily abnormal heart rhythms, but some extra heartbeats we call PVCs-or premature ventricular contractions-or they'll also cause a sensation of palpitations."

Caffeine may help depression

"In low doses, caffeine may help with depression," said Dr. Clark. The reason is because caffeine "stimulates dopamine, which is a chemical in your brain that plays a role in pleasure motivation and learning."

Low levels of dopamine can make you feel tired, moody and unmotivated, among other symptoms, she said. But "having more dopamine helps patients with depression by improving their mood."

Dr. Fernandes cautioned, however, that even though "there is some data that shows caffeine helps with mood," clinical depression requires evidence-based medication and therapy.

"When you drink caffeine, it is rapidly absorbed in the stomach and then the gastrointestinal tract, and then it gets metabolized by some of the enzymes in the liver," Dr. Fernandes said. "Then it causes some hormones-called neurotransmitters-within the nervous system to be more stimulated or excited."

Dr. Devries noted that caffeine is typically absorbed "within 45 minutes and is metabolized in the liver at rates subject to significant genetic variability."

Caffeine "is highly metabolized, with about 3% or less being excreted in the urine," said Dr. Kilgore. "The half-life of the drug typically is around four to five hours, but it can range dramatically from as quickly as an hour and a half to as much as nine hours, depending on genetic factors and coadministration with other medications, including oral contraceptives, and smoking.

"Smokers have massively increased clearance, so they will keep it around for a shorter time," she added, noting that "pregnancy gets greatly reduced metabolism, so women need to watch how much caffeine they're drinking."

Caffeine can interfere with medications

"It's important to tell your doctor about your caffeine intake because it can interfere with medications," said Dr. Fernandes. "For example, if a patient is taking another stimulant medication for ADHD, the combination with caffeine can cause high heart rate, elevated blood pressure and heart palpitations."

Some commonly used medications or supplements that can have diminished effects due to caffeine include iron supplements, thyroid medications, antidepressants and Alzheimer's disease medications.

Then, on the other end, caffeine may increase the absorption or effects of other medications such as acetaminophen, aspirin and a medication for Parkinson's disease.

With insomnia, limit caffeine

"Fortunately, typical intake of caffeine within the range of most coffee and tea drinkers has minimal risk, apart from perhaps difficulty sleeping for some," Dr. Devries said.

"The obvious side effect is that it can cause insomnia because it is intentionally trying to keep someone awake," said Dr. Kilgore. "In people who don't regularly drink caffeine, they're the most vulnerable to the insomnia component.

"Especially if it's consumed later in the day, like late afternoon, it can lead to insomnia and sleeping issues," said Dr. Fernandes. "Some people who use it more chronically might not be as sensitive to those effects, but we tell people to avoid using it later in the afternoon. Try to stick with it earlier in the day if you're going to drink it."

Coffee and tea have health benefits

"Coffee and tea are true feel-good stories in nutrition -we like them, and they like us back," said Dr. Devries. "Both coffee and tea are linked to a host of health benefits, including reduced risk of cardiovascular disease, lower risk of type 2 diabetes and improved longevity.

"Most of the benefits are noted with intake in the range of 2-5 cups per day," he added, noting "the source of the benefits, beyond caffeine, are a wide range of biologically active polyphenols-chemicals with powerful antioxidant and anti-inflammatory properties."

"Caffeine can actually be used as part of medications such as Excedrin [aspirin/paracetamol/caffeine], which is used often to relieve headaches or migraines," Dr. Fernandes said, noting that "what's interesting is that too much caffeine or withdrawal from caffeine can also cause headaches."

Caffeine can help with exercise

"It actually can help exercise as well," said Dr. Kilgore. "It's shown to improve endurance and speed as well as just having a decreased perception of fatigue."

By using caffeine in different forms, "people might be able to maintain exercise longer in a session," she said, noting that "athletes often will take it intentionally before they exercise."

This is because caffeine "is actually a part of some preworkouts to help with increasing motivation as well as helping with endurance," Dr. Fernandes said. But when it comes to preworkout drinks, "be aware of the time that you're taking it because it does have caffeine in it, so if you're taking it right before you're about to go to bed, it's going to have some effects on your sleep."

"Try to be conscious of timing and try to use preworkouts earlier in the day," she said. "And the most important thing is caffeine is a drug, so you can develop tolerance to it-and you can also develop withdrawal from it."

Some people may feel anxious

"There are concerns about increasing anxiety for some people," said Dr. Clark. This is "because caffeine is a stimulant and it stimulates some of the chemicals in your brain, speeding everything up."

"Even in moderate amounts it can cause jitteriness and anxiety," said Dr. Kilgore, noting that caffeine "can also increase respiratory rate, heart rate and blood pressure, which is most often fine in normal people, but if they have a health condition it should be under consideration."

Brewing method affects cholesterol

"Interestingly, brewing method does matter," said Dr. Devries, noting that "unfiltered coffee made with a French press or Turkish style and, to a lesser extent, espresso, are associated with a small but significant increase in LDL cholesterol that does not occur with filtered coffee.

"The reason is that filtered coffee removes much of the cafestol, a compound naturally found in coffee that raises blood cholesterol levels," he added.

There can be withdrawals

"The most common concern about coffee is that it has a withdrawal syndrome," said Dr. Kilgore. When this occurs, "people feel like they need to keep using it, even if they don't need it that particular day for its intended benefit of increasing alertness; and that withdrawal effect can happen as soon as 12 hours after the last coffee in people who use it regularly.

"It can last up to one to two days if intentionally stopped after prolonged use," she added, noting that "some effects can last even up to nine or 10 days with headache, nervousness and fatigue."

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Too much may lead to headaches

"If you consume too much caffeine, it can also cause headaches," said Dr. Clark. This is often in addition to feeling "nervous and anxious."

But caffeine can also "sometimes help headaches," she said, noting that "for some people, it can actually treat their headaches or migraines."

"Caffeine can also be used medically to treat headache because it improves the absorption of other analgesics," said Dr. Kilgore. "It actually causes vasoconstriction. That by itself can also make the headache go away. So, it can cause headaches, and it can also help."

Weight gain may be decreased

"Caffeine can actually decrease weight gain-not necessarily cause weight loss," said Dr. Kilgore. "It increases your base metabolic rate and can suppress appetite a bit, which is useful if someone's thinking of trying to be careful about their weight."

"The important thing, of course, is that in the United States so much of our coffee has all this added cream and sugar, which adds to weight gain," she said. "So that really only pertains to black coffee, which has two calories a cup.

"Because it can make you feel less hungry and reduce cravings, but then for people who always have sugar in their coffee it probably increases cravings because of the sugar," Dr. Kilgore added.

Decaf is not free of caffeine

"Decaffeinated coffee has only slightly lower levels of polyphenols than regular coffee," Dr. Devries said. "Because of the preservation of high polyphenol levels, the association of decaffeinated coffee intake with improved longevity remains."

It is important to point out that "decaffeinated coffee isn't zero caffeine, but certainly much less," said Dr. Kilgore. "A lot of people think it's without caffeine, but it's not. It's about 2 to 15 milligrams, so certainly far less than caffeinated.

"But even if you went to decaf, you would probably have some withdrawal symptoms if you don't withdraw judiciously," she added.

Try to avoid energy drinks

"The more serious risks of caffeine are mostly related to heavy consumption from use in energy drinks and in supplement form," said Dr. Devries. "Anxiety and unsafe behaviors-especially in adolescents-are associated with energy drink use.

"High blood pressure, palpitations and arrhythmias are other possible risks with high intake of supplemental caffeine," he added.

"In general, I do try to counsel my patients to avoid energy drinks or caffeine energy supplements as much as possible because you see more side effects when people use them," Dr. Fernandes said. "If you're going to use them, definitely let your doctor know because some of the symptoms that you might be seeing us for might be related to it."

Don't cut caffeine right away

"It's important to know how much you're drinking in the first place, so really be honest with yourself about how much you're drinking and keep track of it for a few days," said Dr. Kilgore. "This will allow you to get a true sense of how much caffeine you're consuming."

"If you consume a lot of caffeine regularly and then you abruptly stop without gradually tapering off of it, you can definitely develop headaches," said Dr. Fernandes.

But if you need to reduce the amount of caffeine you are consuming, "slowly decrease your intake," said Dr. Clark. This means you can "do half caffeinated or you can mix in some decaffeinated beverages in sodas and coffee."

"Don't cut out caffeine completely all of a sudden because then you may experience some bad withdrawal syndromes," she said. "If you need help with how to decrease your intake or you're getting headaches when you're trying to go off caffeine, talk to your doctor."

Decrease intake if pregnant

For people who are pregnant, "you should decrease your intake of caffeine," said Dr. Clark. This is because "the caffeine does go to the baby and can speed up the baby's heart rate."

Additionally, "the baby can become dependent on caffeine and have withdrawals when the baby is born," she said. That's why "you should dramatically limit your caffeine intake when pregnant."

The American College of Obstetrics and Gynecology recommends that those who are pregnant limit caffeine intake to less than 200 milligrams per day.

Talk with your doctor

"If you do have questions about caffeine , definitely chat with your doctor about it," Dr. Fernandes said, "especially if you're worried that you might be consuming too much, if you're nervous about some of the side effects, or if you have questions about energy drinks.

"I see a lot of patients with side effects from energy drinks," she added. "So, if you're concerned at all about caffeine, definitely have a conversation with your doctor about it."

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What doctors wish patients knew about the impact of caffeine

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Caffeine can be part of a healthy diet for most people, but too much may pose a danger to your health. Four physicians share what to keep in mind.

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Women's Health Food and Nutrition Nutrition and Fitness Diagnosis and Screening for Gynecologic Conditions

Ah, coffee. Whether you're cradling a travel mug on your way to work or dashing out after spin class to refuel with a skinny latte, it's hard to imagine a day without it. The caffeine perks you up, and there's something incredibly soothing about sipping a steaming cup of joe. But is drinking coffee good for you?

Good news: The case for coffee is stronger than ever. Study after study indicates you could be getting more from your favorite morning beverage than you thought: Coffee is chock full of substances that may help guard against conditions more common in women, including Alzheimer's disease and heart disease.

Caffeine is the first thing that comes to mind when you think about coffee. But coffee also contains antioxidants and other active substances that may reduce internal inflammation and protect against disease, say nutrition experts from Johns Hopkins University School of Medicine.

What are the top health benefits of drinking coffee?

Your brew gives you benefits beyond an energy boost. Here are the top ways coffee can positively impact your health:

1. You could live longer.

Recent studies found that coffee drinkers are less likely to die from some of the leading causes of death in women: coronary heart disease, stroke, diabetes and kidney disease.

2. Your body may process glucose (or sugar) better.

That's the theory behind studies that found that people who drink more coffee are less likely to get type 2 diabetes.

3. You're less likely to develop heart failure.

Drinking one to two cups of coffee a day may help ward off heart failure, when a weakened heart has difficulty pumping enough blood to the body.

4. You are less likely to develop Parkinson's disease.

Caffeine is not only linked to a lower chance of developing Parkinson's disease, but it may also help those with the condition better control their movements.

5. Your liver will thank you.

Both regular and decaf coffee seem to have a protective effect on your liver. Research shows that coffee drinkers are more likely to have liver enzyme levels within a healthy range than people who don't drink coffee.

6. Your DNA will be stronger.

Dark roast coffee decreases breakage in DNA strands, which occur naturally but can lead to cancer or tumors if not repaired by your cells.

7. Your odds of getting colon cancer will go way down.

One in 23 women develop colon cancer. But researchers found that coffee drinkers - decaf or regular - were 26 percent less likely to develop colorectal cancer.

8. You may decrease your risk of getting Alzheimer's disease.

Almost two-thirds of Americans living with Alzheimer's disease are women. But the caffeine in two cups of coffee may provide significant protection against developing the condition. In fact, researchers found that women age 65 and older who drank two to three cups of coffee a day were less likely to develop dementia in general.

9. You're not as likely to suffer a stroke.

For women, drinking at least one cup of coffee a day is associated with lowered stroke risk, which is the fourth leading cause of death in women.

5 Heart-Healthy Food Swaps

How much coffee is safe for women to drink each day?

It's true, you can have too much of a good thing. Excessive intake of caffeinated coffee can make you jittery and cause:

Increased heart rate

Raised blood pressure

Anxiety

Trouble falling asleep

So how much coffee is the optimal amount to drink to get all the benefits, but avoid the negative side effects?

According to the Dietary Guidelines for Americans, it's safe for most women to drink three to five cups of coffee a day with a maximum intake of 400 milligrams of caffeine. (Caffeine content can vary depending on the type of coffee, but an average 8-ounce cup has 95 milligrams.)

But if you're pregnant or breastfeeding, the rules are different. Check with your obstetrician before adding caffeine into your diet. If coffee gives you the jitters, take care not to overdo it: Caffeine tolerance is different for everyone. You can still get some of the potential health benefits by drinking one cup of coffee a day, or even decaf.

Also, remember that what you add to your coffee can make a difference in how healthy the beverage really is. Instead of loading up on cream and sugar, try adding up to two tablespoons of milk, milk substitute or half-and-half, and using naturally sweet spices and flavorings. Try stirring in a ¼ teaspoon of the following for extra flavor:

While coffee is a pleasurable part of your lifestyle, there are other factors that make a bigger impact on your health such as eating a balanced diet, exercising and maintaining a healthy weight. But drinking coffee is a delightful addition to those key health factors.

Johns Hopkins nutritionists share a recipe for a healthy iced pumpkin spice "latte" smoothie.

Quick & Healthy Coffee Recipe

Iced Pumpkin Spice "Latte" Smoothie

Blend all ingredients to create a seasonally-inspired drink. Using real pumpkin adds beneficial fiber.

1 cup coffee

½ cup milk of your choice (such as unsweetened vanilla flavored almond milk, skim or 1% milk)

2 teaspoons pumpkin pie spice (or ½ teaspoon each ground cinnamon, nutmeg, ginger and allspice)

1 teaspoon vanilla extract

½ cup canned plain pumpkin

4 ice cubes

Try to limit added sugar as much as you can! If you MUST add sweetener, try pure maple syrup in a small quantity- start with 1 teaspoon.

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9 Reasons Why (the Right Amount of) Coffee Is Good for You

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A Johns Hopkins research nutritionist shares the benefits of coffee and a recipe for a healthy pumpkin spice latte smoothie.

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Caffeine’s Side Effects | Aurora Health Care

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Learn about caffeine’s many side effects, such as trouble sleeping, anxiety, heartburn, dizziness, shakiness, and elevated heart rate and blood pressure.

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From coffee and tea to energy drinks, caffeine is easy to find. Teens often reach for these drinks before a sports event or a long study session. And while it's true that caffeine may give them an energy boost or help them focus, drinking too much of it could be bad for their health.

This article discusses the short and long-term health effects that caffeine can have on teens. It includes the signs you should know that your teen drank too much caffeine and ways you can limit their intake.

What Is Caffeine?

Caffeine comes from natural sources. It's in coffee beans, cacao (where chocolate comes from), tea leaves, and more. Manmade forms are also added to certain foods and drinks.

Caffeine is a type of drug known as a stimulant. This means that it excites the central nervous system, making the person who drinks it more alert. Many people find that caffeine gives them a temporary energy boost and can even brighten their mood.

An estimated 80% of people worldwide consume caffeinated products every day. This includes roughly 73% of children. Fewer teens are drinking soda compared to a decade ago. However, teens are still drinking plenty of caffeine, turning to coffee and energy drinks instead.

Side Effects

Research shows that small doses of caffeine can:

Enhance your mood

Make you more alert

Help you process information faster

Boost your awareness

Help you focus

Speed up your reaction time

That said, most of the research has focused on adults, not children. And not all research on caffeine shows positive side effects either.

Caffeine can cause a number of unwanted side effects in both teens and adults. Some people are more sensitive to caffeine than others. For these more sensitive people, just a small amount of caffeine may produce unwanted effects.

Multiple studies have shown many unwanted side effects of caffeine including:

Restlessness

Nervousness

Flushed face

Diuresis (increased urination)

Upset stomach

Muscle twitching

Rambling speech and thoughts

Tachycardia or cardiac arrhythmia (irregular heart rhythms)

Pacing, tapping toes, pulling at clothes, and other forms of psychomotor agitation

The effects of caffeine can start within a few minutes after you consume it. This drug has a half-life of around five to six hours. In other words, after you consume it, it takes five to six hours for there to be half as much caffeine in your blood.

Recap

Health Consequences

Adolescence is a vital time for brain development. The brain has the most neural connections ( synapses) during these years, and they will keep maturing well into your mid-twenties.

Research shows that drinking caffeine from a young age can stunt brain development. That's because caffeine can make these growing connections less efficient and stop them from forming.

Caffeine triggers pleasure circuits in the brain's reward system. It gives your brain a burst of dopamine (the happy hormone). This is the same process that leads to drug addiction.

It is thought that caffeine's effect on the brain's reward and addiction center may influence a child's food and drink preferences later in life.

Here are a few other ways that caffeine can impact teens and adolescents:

Caffeine takes a major toll on a teen's sleep. Every 10mg of caffeine a 13-year-old boy consumes cuts his chances of getting 8.5 hours of sleep by 12%. Sleep deprivation (lack of sleep) in teens can affect their education, mental health, and physical health.

Caffeine may also cause the body to lose calcium. Consuming too much caffeine could lead to bone loss over time. Additionally, soft drink consumption has been linked to a higher incident of fractures, Drinking soda or energy drinks instead of milk can also raise a teen's risk of osteoporosis down the line.

Caffeine may worsen underlying health issues, like heart problems. It can also interact with certain medicines or supplements.

Recap

Gender Differences

Researchers have found that caffeine affects children of any sex the same prior to puberty. Once puberty passes, caffeine starts to affect males and females in different ways.

Overall, teen boys show a greater response to caffeine than teen girls. Girls are more likely to have a slower heart rate than boys after being given caffeine. Meanwhile, girls are more likely to have increased diastolic blood pressure. Diastolic blood pressure is the bottom number in a blood pressure reading. It stands for the amount of pressure in the arteries when the heart rests between beats.

Caffeine Dependence in Teens

Many people report feeling "addicted" to caffeine. They may have trouble quitting or cutting back on their caffeine intake. Some people continue consuming it even though they experience unwanted side effects.

Regular caffeine drinkers may have symptoms of withdrawal when they stop consuming it. Researchers have found that children and teens may go through withdrawal after they've cut out caffeine as well.

Withdrawal symptoms vary in severity. Common withdrawal symptoms include:

Headache

Fatigue

Sleepiness

Trouble concentrating

Difficulty completing tasks

Irritability

Depression

Anxiety

Flu-like symptoms (nausea/vomiting, muscles aches, hot and cold spells)

Impaired psychomotor and cognitive performance

Common Sources

Here are some of the most common sources of caffeine that appeal to teens:

Peach Snapple: 42mg (16 ounces)

Monster Energy Drink: 160mg (16 ounces)

Starbucks Frappuccino: 115mg (9.5 ounces)

Mountain Dew: 55mg (12 ounces)

Instant coffee: 31mg (1 tsp)

Brewed coffee: 95-200mg (8 ounces)

Iced tea: 70mg (12 ounces)

Most people know that coffee and certain soft drinks contain caffeine. But there are also some less obvious caffeine sources that parents and teens should know of, such as:

Dark chocolate: 18mg (1.45 ounces)

Clif Bar Peanut Toffee Buzz: 50mg (2.4 ounces)

Hot chocolate: 3-13mg (8 ounces)

Dannon All-Natural coffee yogurt: 30mg (6 ounces)

Vitamin Water Energy: 50mg (20 ounces)

Recap

Should Teens Consume Energy Drinks?

The American Academy of Pediatrics has taken a clear stance on energy drinks: They have no place in the diets of children and adolescents.

Some parents confuse energy drinks with sports drinks. Many teens mistake energy drinks as being healthier than soda too.

It doesn't help that energy drinks are often marketed to youth. Companies that make these drinks often sponsor sports events that appeal to teens. Such events make it seem that energy drinks are a good choice for young athletes to drink.

Energy drinks contain other substances that can be unhealthy for teens. Some contain guarana, which comes from a plant found in South America. Although it contains caffeine, it's not often thought of as a caffeinated product.

Energy drinks can also contain amino acids, vitamins, and additives. The effects of these substances are largely unknown.

Overdose and Toxicity

Many teens and young adults have overdosed on caffeine. In 2009 alone, The Substance Abuse and Mental Health Services Administration reported more than 13,000 emergency room visits related to energy drinks.

Between 2007 and 2011, the number of energy drink-related visits to emergency departments doubled. In 2011, one in 10 of these visits resulted in hospitalization.

Caffeine toxicity can be fatal. Logan Stiner, a high school student from Ohio, had a cardiac arrhythmia and a seizure after using powdered caffeine. Doctors learned he took more than a teaspoon of the powder. This was 16 times the recommended dose.

Caffeine powder is usually sold as a dietary supplement, so the FDA does not regulate it. It can easily be bought on the internet.

Several other deaths have been linked to caffeine overdose. An investigation by in 2012 found at least 13 deaths linked to energy drinks.

Recap

Limiting Caffeine for Teens

You can't control all the things your teen chooses to eat and drink when you're not around. But, you can teach them healthy habits and limit their caffeine intake. Here are some steps you can take to protect your teen from the dangers of caffeine:

Stock up Smartly

Don't stock the fridge with soft drinks. Don't buy teas, energy drinks, and other beverages with a lot of caffeine. Try to make it a habit for your family to drink water and low-fat milk instead.

Educate Yourself

Nutrition labels don't list how much caffeine a product has. If you find that your teen is drinking caffeine, do a quick internet search for the product's ingredient list. This list will show how many milligrams are in the product.

Talk About It

Many caffeinated drinks contain a lot of sugar, which can contribute to obesity and tooth decay. So limiting caffeine could be better for your teen's overall health. Make sure your teen knows that energy drinks and sugary teas aren't good for them.

Talk to your teen about the dangers of caffeine in the same way you talk about drugs or alcohol. Warn your teen that too much caffeine could cause serious health problems.

Be a Good Role Model

If you turn to coffee to help you function, or you down an energy drink before you head out for a night on the town, your teen may grow to think stimulants are a normal part of adult life. And that could lead them to develop bad habits.

Limit Afternoon and Evening Caffeine

Drinking a Frappuccino after school or a soda after basketball practice could keep your teen up half the night. If they are going to have caffeine, make sure it's early in the day.

Know the Warning Signs

Look out for signs that your teen is consuming a lot of caffeine. If your teen is jittery or not sleeping well, look into what they have been eating and drinking.

Help Your Teen Cut Back

If your teen regularly consumes more caffeine than they should, help them to cut back. Be aware they may have some unpleasant withdrawal symptoms if they suddenly quit caffeine altogether.

Recap

Caffeine is easy for teens to get ahold of. It's in coffee, tea, energy drinks, chocolate, and even protein bars. It's also sold online in powdered form, where it is often marketed as a supplement.

Caffeine overdose is a real risk for people of all ages. Educate your teen about the dangers of caffeine and be a good role model for them. Make sure your family knows the risks that caffeine poses, and the signs they have had too much.

Frequently Asked Questions

Can caffeine stunt a teenager's growth?

Though caffeine affects calcium absorption, studies have not found evidence that it stunts bone growth. Lack of sleep due to caffeine has not been found to affect growth either.

How much caffeine per day is OK for a teenager?

Most children's health experts agree that kids between 12 and 18 years of age should not have more than 100mg of caffeine each day. That roughly amounts to:

One cup of coffee

One or two cups of tea (depending on how strong it is)

Two 12-ounce sodas

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Learn if You Should You Let Your Teenager Drink Caffeinated Drinks

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Teens may reach for energy drinks before a game or to turn to coffee to help them pull an all-night study session. See the effects on a teen's health.