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Pierre Maurage,

3Psychological Science Research Institute, Catholic University of Louvain, Belgium

4Institute of Neuroscience, Catholic University of Louvain, Belgium

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Alexandre Heeren,

3Psychological Science Research Institute, Catholic University of Louvain, Belgium

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Mauro Pesenti

3Psychological Science Research Institute, Catholic University of Louvain, Belgium

4Institute of Neuroscience, Catholic University of Louvain, Belgium

Author disclosures: P. Maurage, A. Heeren, and M. Pesenti, no conflicts of interest.

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1
P. Maurage and M. Pesenti are research associates and A. Heeren is a post-doctoral researcher funded by the National Fund for Scientific Research (Belgium).

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Received:

28 January 2013

Revision received:

18 March 2013

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Pierre Maurage, Alexandre Heeren, Mauro Pesenti, Does Chocolate Consumption Really Boost Nobel Award Chances? The Peril of Over-Interpreting Correlations in Health Studies, The Journal of Nutrition, Volume 143, Issue 6, June 2013, Pages 931–933, https://doi.org/10.3945/jn.113.174813

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Abstract

A correlation observed between chocolate consumption and the number of Nobel laureates has recently led to the suggestion that consuming more chocolate would increase the number of laureates due to the beneficial effects of cocoa-flavanols on cognitive functioning. We demonstrate that this interpretation is disproved when other flavanol-rich nutriment consumption is considered. We also show the peril of over-interpreting correlations in nutrition and health research by reporting high correlations between the number of Nobel laureates and various other measures, whether cogently related or not. We end by discussing statistical alternatives that may overcome correlation shortcomings.

A recent note in the New England Journal of Medicine reports a high correlation between chocolate consumption and the number of Nobel laureates, taken as a proxy of a population's global cognitive level, in 23 countries all over the world (1). This, the author argues, would be due to the beneficial effect of the flavanols contained in cocoa. This subclass of polyphenol-flavanoids present in various plant-based foods (2) would indeed play a preventive role against neurodegenerative diseases and, more globally, might have a positive impact on cognitive functioning (3–5). As a direct consequence of this surprising correlation, the author of the note suggests increasing the quantity of chocolate intake to improve cognitive abilities at the individual level, which will in turn increase the number of Nobel laureates at the national level. Whereas the second part of this provocative conclusion may have been made humorously, the first one was taken very seriously in recent scientific publications [e.g., (6,7)] and has received wide coverage in the popular media. However, as appealing and intriguing as it may sound, this conclusion must be taken very cautiously, as it goes in fact far beyond the data. In the following discussion, we show that it must be questioned on methodological, statistical, and logical grounds.

At the methodological level, it is worth noting that the observed correlation is in fact based on country-averaged chocolate consumption and not on the actual consumption of Nobel laureates themselves. This causes a major interpretation problem known as ecological inference fallacy, where conclusions about individual behaviors are drawn from data about aggregate behaviors, with no guarantee that the relationships observed at the group level necessarily hold for individuals (8) [for an application of this problem to health-environmental exposure issues, see (9)]. Moreover, the correlated data concern the last 2 y for chocolate consumption, whereas they spread over more than a century for Nobel laureates. This temporal gap clearly limits the pertinence of this correlational analysis, as chocolate consumption habits have radically changed over the past decades [e.g., the worldwide production of cocoa has quadrupled between 1960 and 2010 (10)], and recent consumption thus cannot be taken as a good estimator of past periods. More importantly, chocolate is only one of the many nutriments containing flavanoids. Should the quantity of flavanoids in nutriments indeed be the crucial explanatory factor, then the number of Nobel laureates should also correlate with the consumption of other flavanoid-rich nutriments. We, however, did not observe such a correlation with the mean annual tea (r = 0.03; P= 0.88) (Fig. 1A) and wine (r = 0.16; P= 0.47) (Fig. 1B) consumption per capita in the same 23 countries (11) even though these nutriments both present very high flavanoid concentrations (12). Thus, flavanoid concentration does not fully explain the high chocolate–Nobel laureate correlation.

FIGURE 1

Correlations between countries' (A) number of Nobel laureates per ten million population and annual per capita tea consumption; (B) number of Nobel laureates per ten million population and annual per capita wine consumption; (C) number of Nobel laureates and number of IKEA stores per ten million population; (D) number of Nobel laureates per ten million population and annual per capita gross domestic product; and (E) annual per capita chocolate consumption and annual per capita gross domestic product.

FIGURE 1

Correlations between countries' (A) number of Nobel laureates per ten million population and annual per capita tea consumption; (B) number of Nobel laureates per ten million population and annual per capita wine consumption; (C) number of Nobel laureates and number of IKEA stores per ten million population; (D) number of Nobel laureates per ten million population and annual per capita gross domestic product; and (E) annual per capita chocolate consumption and annual per capita gross domestic product.

At the statistical level, it is worth recalling that correlation never implies causation. There are many examples of correlations for which causal interpretations do not make sense [e.g., (13)]. Let us prove again this caveat by reducing it to the absurd within the present context. We found an incredibly high correlation between the number of IKEA furniture stores (14) and Nobel laureates (r= 0.82; P< 0.0001) (Fig. 1C), although we could not come up with any mutual causal relationship - and we doubt that someone would seriously claim that IKEA mainly limits its market to countries awarded the Nobel prize or that the need to understand and apply IKEA's furniture assembly instructions improves cognitive functioning at the population level.

At the logical level, even when keeping in mind that correlation does not mean causation, it is tempting to infer some loose directionality between factors when high correlations come along with sound interpretations. After all, a beneficial effect of flavanoid consumption on cognitive functioning on populations is plausible and certainly sounds more logical than the reverse effect of Nobel awards possibly leading to greater consumption of chocolate. Accordingly, although the author of the note acknowledges that the observed correlation cannot be directly interpreted as reflecting a causal link, the discussion tends to exclude alternative explanations and proposes that higher chocolate consumption will increase the number of Nobel laureates. However, even with an apparently meaningful relation, such an interpretational drift from correlation to directionality must never be allowed, because, as hidden factor(s) influencing both variables separately cannot be excluded, a third cause fallacy could always be involved. In the present case, e.g., we reasoned that the Gross Domestic Product (GDP; i.e., country market value of all final goods and services per year per capita) taken as an indicator of a country‘s standard of living could mediate both luxury food consumption and the level of scientific research. As we suspected, it turned out that the GDP (15) strongly correlated both with the number of Nobel laureates (r= 0.66; P < 0.001) (Fig. 1D) and chocolate consumption (r= 0.73; P< 0.001) (Fig. 1E). Moreover, using the Fisher r-to-z transformation that allows statistical comparison of the strength of different correlations, we found that the original chocolate-Nobel correlation (r= 0.79; P< 0.0001) is not significantly stronger than the GDP-Nobel (Fisher z-test = 0.49, NS) or than the GDP-chocolate (Fisher z-test = 0.9, NS) correlations observed here.

Experimental designs or intervention trials should always be preferred when researchers want to examine cause-to-effect relationships. When this is not possible and a correlational design is the only solution, 2 mathematical methods, Granger causality and Convergent Cross Mapping (CCM) tests, have been specifically developed to approach causality. The Granger causality test assesses whether a sequence of data points is useful to predict another based on linear regression modeling of stochastic processes (16,17): if a X₁ “Granger-causes” X₂, then past values of X₁ should contain information that helps predict X₂ above and beyond the information contained in past values of X₂ alone. Concretely, once a correlation is found, the Granger causality test can be used to strengthen the case that there is a causal link at work (18). However, when causality runs both ways (e.g., in the relation between sport and excess weight, limited physical activity favors weight increase and excess weight leads to reduced physical activity), CCM can be used instead of the Granger causality test. Based on nonlinear state space reconstruction, CCM mathematically transforms each data set to create a 3-dimensional shape called a manifold (19). Points on one manifold are used to predict points on the other, but not necessarily the other way round, allowing causal relationships of one direction or another to be measured separately. Although the application of these methods has just begun [see e.g. (20)], we think that they constitute a good alternative when experimental designs are not possible.

Correlations tell the researchers the degree of relationship between factors; no more, no less. They prove useful in understanding which factors are related and in generating hypotheses for further experimental testing. Our discussion of a recent report attributing beneficial effects to chocolate consumption shows the peril of over-interpreting correlations. In nutrition research, such erroneous inferences may have dramatic effects, as they may lead to attributing beneficial (or harmful) effects to a wrong cause, hence representing a real danger for health. We hope we have helped readers to correctly situate the relevance of the initial report and to avoid misinterpretations of correlations that hamper nutrition and health research.

Acknowledgments

P.M., A.H., and M.P. designed research; P.M. performed statistical analyses; and P.M., A.H., and M.P. wrote the paper. All authors read and approved the final manuscript.

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Author notes

1
P. Maurage and M. Pesenti are research associates and A. Heeren is a post-doctoral researcher funded by the National Fund for Scientific Research (Belgium).

© 2013 American Society for Nutrition

© 2013 American Society for Nutrition

Topic:

awards and prizes

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cognitive ability

cocoa

chocolate

flavanol

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# data[].attributes.attachment_link.title
Does Chocolate Consumption Really Boost Nobel Award Chances? The Peril of Over-Interpreting Correlations in Health Studies

# data[].attributes.attachment_link.description
Abstract. A correlation observed between chocolate consumption and the number of Nobel laureates has recently led to the suggestion that consuming more chocolat

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https://www.nicswell.co.uk/health-news/can-chocolate-make-you-smarter#:~:text=They%20found%20that%20people%20who,rarely%20or%20never%20ate%20chocolate.

# data[].attributes.attachment_link.readable_text
"Chocolate makes you smarter, proves 40-year study," claims the Daily Express. The news is based on research which found that people who ate chocolate at least once a week performed better in brain tests.

Researchers in the US looked at whether eating chocolate regularly - regardless of the type of chocolate or the amount - was linked to brain function, in about 1,000 participants.

They found that people who said they ate chocolate at least once a week performed better in a range of mental tests involving memory and abstract thinking (among other functions), compared to those who rarely or never ate chocolate.

Lead researcher Georgina Crichton was quoted in the media as saying that the benefits of this would make someone better at daily tasks, "such as remembering a phone number, or your shopping list, or being able to do two things at once, like talking and driving at the same time".

The researchers said their results suggest that the "regular intake of cocoa flavanols may have a beneficial effect on cognitive function".

There have been plenty of studies in recent years looking at the possible health benefits of chocolate, including preventing heart disease and stroke, and improving brain function.

Due to the nature of the study, researchers admit they are unable to say whether the chocolate was responsible for the improved performance in the tests. Plenty of other factors could have been involved.

Before getting too carried away with the supposed health benefits of chocolate, it's worth remembering that chocolate also contains lots of sugar and fat, so should only be eaten in moderation.

Where did the story come from?

The study was carried out by researchers from the University of South Australia, the University of Maine and the Luxembourg Institute of Health, and was funded by the National Institutes of Health. The study was published in the peer-reviewed journal Appetite.

The study received widespread and mostly uncritical coverage by the UK media. The Independent and Daily Express both said that the study gave "proof" that chocolate made people more intelligent, while The Daily Telegraph and Daily Mirror said chocolate "can make you smarter".

However, The Guardian took a more sceptical approach, saying the results were "very vague" and taking the opportunity to question other health claims made for chocolate.

What kind of research was this?

This was a cross-sectional analysis of data from a big cohort study, which follows people through time. However, in this case, the researchers used data from just one time point, giving a "snapshot" of people's diet and brain function tests.

Studies like this can point to links between factors, but cannot demonstrate cause and effect. For example, it could be that chocolate makes people clever - or that clever people tend to eat more chocolate.

What did the research involve?

Researchers looked at the data from about 1,000 people taking part in a US cohort study (the Maine-Syracuse Longitudinal Study, MSLS) which was set up to examine cardiovascular risk factors and brain function in community-dwelling adults. As part of this study, participants filled in food questionnaires and undertook brain function tests from 2001 to 2006.

The researchers adjusted the figures to take account of factors that could skew the results, including people's education level, age, cardiovascular risk factors, and overall diet. They then looked to see whether brain test results varied according to how often people said they ate chocolate.

They excluded people with dementia, a history of stroke and past problems with alcohol use. While the main analysis of 968 people was based on one-off data for each individual, they also looked at data from a sub-group of 333 people who had taken intelligence tests in the past, before providing dietary information. They wanted to see whether intelligence scores could predict whether or not people said they ate chocolate frequently.

People in the study underwent brain function tests in six main areas:

visual-spatial memory and organisation

scanning and tracking

ability to remember spoken information, such as a story or a list

working memory

similarities test (to assess abstract reasoning)

mini-mental state exam

The researchers combined the first five to create an overall score.

The researchers took account of a few variables that could affect the results - such as people's education level, age, sex, overall diet and cardiovascular risk.

What were the basic results?

After adjusting their figures for confounding factors, the researchers found that better-than-average scores on five of the brain function area tests, and the overall score, were linked to eating chocolate more often (at least once a week compared to rarely or never). Tests of verbal memory showed no link to chocolate consumption.

Eating chocolate once a week, or more than once a week, was also linked to above-average test results, compared to eating it less than once a week. However, it's not clear whether eating chocolate more than once a week was linked to better test results than eating it weekly.

When the researchers looked at the subgroup of people who'd had intelligence tests in the years before the dietary questionnaire, they found that intelligence scores did not predict whether or not people ate chocolate.

How did the researchers interpret the results?

The researchers said their results, along with those of other short-term studies, suggest that, "regular intake of cocoa flavanols may have a beneficial effect on cognitive function, and possibly protect against normal age-related cognitive decline."

They add that people will need to strike a balance between the supposed health benefits of eating chocolate and its high-calorie content.

Conclusion

Studies suggesting that chocolate is good for us always grab the headlines. However, as is so often the case, the reality is less clear than the headlines suggest.

The current study adds to information about the links between diet and brain function - the way our brain processes and manages information.

It found that people who scored better than average on these tests said they ate chocolate more often than people who scored worse than average on the tests. But we don't know why that is.

There are quite a few limitations to the study. It's cross-sectional, which means we don't know which came first: the chocolate habit or the better brain function scores. It only shows us results from one snapshot in time.

There are many factors that are hard to account for that could affect how much chocolate you eat, and how well you do on brain function tests - for example, the family you grew up in. We can't be sure chocolate was the only factor that mattered. We also don't know how much chocolate people ate (only how often they ate it) or what type - whether it was dark, milk or white chocolate.

It's not easy to do good-quality, long-term studies into the effects of diet on health or intelligence, but we need to see much more, and better, long-term research before we can conclude that chocolate makes you smarter.

And even if cocoa flavanols do have some benefits, it's worth remembering that chocolate also contains lots of fat and sugar, which can contribute to obesity.

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well is a programme incorporating support

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education and information on a wide range of health and wellbeing issues which is available to all northern ireland civil service staff

# data[].attributes.attachment_link.title
Can chocolate make you smarter? | NICS Well

# data[].attributes.attachment_link.description
"Chocolate makes you smarter, proves 40-year study," claims the Daily Express. The news is based on research which found that people who ate chocolate at least once a week performed better in brain tests. Researchers in the US looked at whether eating chocolate regularly - regardless of the type of chocolate or the amount - was linked to brain function, in about 1,000 participants.

# data[].attributes.body
https://www.frontiersin.org/articles/10.3389/fnut.2017.00019/full

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Department of Biotechnological and Applied Clinical Sciences, University of L'Aquila, L'Aquila, Italy

Department of Life, Health and Environmental Sciences, University of L'Aquila, L'Aquila, Italy

Department of Psychology, "Sapienza" University of Rome, Rome, Italy

Enhancing cognitive abilities has become a fascinating scientific challenge, recently driven by the interest in preventing age-related cognitive decline and sustaining normal cognitive performance in response to cognitively demanding environments. In recent years, cocoa and cocoa-derived products, as a rich source of flavonoids, mainly the flavanols sub-class, have been clearly shown to exert cardiovascular benefits. More recently, neuromodulation and neuroprotective actions have been also suggested. Here, we discuss human studies specifically aimed at investigating the effects of acute and chronic administration of cocoa flavanols on different cognitive domains, such as executive functions, attention and memory. Through a variety of direct and indirect biological actions, in part still speculative, cocoa and cocoa-derived food have been suggested to possess the potential to counteract cognitive decline and sustain cognitive abilities, particularly among patients at risk. Although still at a preliminary stage, research investigating the relations between cocoa and cognition shows dose-dependent improvements in general cognition, attention, processing speed, and working memory. Moreover, cocoa flavanols administration could also enhance normal cognitive functioning and exert a protective role on cognitive performance and cardiovascular function specifically impaired by sleep loss, in healthy subjects. Together, these findings converge at pointing to cocoa as a new interesting nutraceutical tool to protect human cognition and counteract different types of cognitive decline, thus encouraging further investigations. Future research should include complex experimental designs combining neuroimaging techniques with physiological and behavioral measures to better elucidate cocoa neuromodulatory properties and directly compare immediate versus long-lasting cognitive effects.

Introduction

With the increase in general population aging, age-related cognitive decline has progressively become a major public health issue. Consequently, enhancing cognitive resources came to be a priority scientific challenge, mainly driven by the need to detect preventive agents for cognitive decline and dementia. At the same time, immediate cognitive enhancement is often desirable in cognitively demanding environments. Stimulants such as caffeine are indeed commonly used to sustain cognitive performance during periods of fatigue and prolonged wakefulness ( 1).

In the last years, the field of nutraceuticals and functional food has developed along with the interest in the potential modulatory effects of food constituents on human health. In this context, there has been increasing interest in the biological effects of flavonoids, a class of polyphenolic compounds, as potential nutraceuticals with several beneficial biological actions, including cardioprotection, neuroprotection, and neuromodulation. Particularly, cocoa bean has been recognized as a rich source of flavonoids, mainly the flavanols subclass in the form of epicatechin and catechin ( 2).

Chocolate also contains other functional ingredients, such as the methylxanthine caffeine and theobromine, with the potential to influence neurocognitive function. However, relative to total flavanols content, caffeine and theobromine concentrations in cocoa and chocolate have been considered lower than those required to exert significant pharmacological actions ( 3).

Epidemiologic studies suggest that a regular intake of flavonoids could be associated with better cognitive function ( 4), decreased risk of dementia ( 5) and cognitive decline ( 6), lower prevalence of cognitive impairment ( 7), better cognitive evolution over a 10-year period ( 8), and better dose-dependent cognitive performance in normal aging ( 9).

The specific mechanisms of action of flavonoids responsible for cognitive protection and modulation are not entirely elucidated. Nevertheless, increasing evidence supports the notion that cocoa and chocolate consumption provides several health benefits, including neurocognitive enhancement and neuroprotective effects. In this brief review, we discuss human studies specifically aimed at investigating the effects of acute and chronic administration of cocoa flavanols on cognition.

Enhancing Cognition with Cocoa Flavonoids: Direct Versus Indirect Mechanisms of Action

The beneficial effects of polyphenolic compounds have been first attributed to their ability to exert antioxidant actions ( 10). However, due to the very low concentration of flavonoids detectable in the brain, it is unlikely that direct antioxidant action can entirely account for cognitive effects in vivo. Instead, flavonoids' neurobiological effects are now believed to be mediated by a range of actions involving the ability to protect vulnerable neurons, enhance neuronal function, and stimulate regeneration via interaction with neuronal intracellular signaling pathways involved in neuronal survival and differentiation, long-term potentiation (LTP), and memory ( 11).

Flavonoids can counteract neuronal injury underlying neurodegenerative diseases such as Parkinson and Alzheimer diseases through their interaction with signaling proteins important in the pro-survival pathways ( 12). Interestingly, flavonoids and their metabolites cross the blood-brain barrier and have been localized in the brain, particularly in areas crucial for learning and memory such as hippocampus, cerebral cortex, cerebellum, and striatum ( 13- 15). These structures are particularly vulnerable to the effects of aging and neurodegeneration, suggesting that flavonoids could exert direct neuroprotective effects ( 16). Direct interactions within several cellular signaling pathways have been described, such as mitogen-activated protein kinase, extracellular signal-regulated kinase, and phosphoinositide 3-kinase (PI3-kinase/Akt) signaling cascades ( 17), that are crucially involved in triggering gene expression and protein synthesis for LTP ( 18). In memory-related areas such as the hippocampus, flavonoids promote the expression of brain-derived neurotrophic factor (BDNF), that is crucial to adult neurogenesis, synaptic growth, and neuronal survival ( 19). Increasing evidence from animal models indicates that flavonoids can promote cognitive benefits through their ability to directly interact with the cellular and molecular architecture involved in memory function ( 2, 11, 12). To date, however, it is still not entirely clear whether and to what extent these direct biological actions also extend to the human brain.

Flavonoids could also display their neurocognitive effects indirectly, through their capability of inducing cardiovascular actions. In this regard, cardiovascular benefits of cocoa and chocolate consumption are now well established and include endothelium-dependent vasodilation, which contributes to the maintenance of normal blood flow, reduced platelet aggregation, and blood pressure improvement ( 20- 26).

Importantly, flavanols such as epicatechin can improve endothelial function by increasing the nitric oxide (NO) bioavailability, a key regulator of vascular function, leading to improvements in vascular tone and blood pressure regulation ( 27, 28). These peripheral vascular changes may also extend to brain perfusion, leading to a more efficient cerebrovascular coupling during neuronal activation, which is considered crucial for the functional and structural integrity of the brain. Moreover, as increased cerebrovascular function promotes adult neurogenesis in the hippocampus ( 29), flavonoid-mediated vascular changes could be additionally relevant for memory function.

Coherently, increasing evidence highlights the potential of cocoa flavanols to influence cognitive abilities interacting with the cerebrovascular system. Flavanol-rich cocoa has been shown to significantly increase cerebral blood flow (CBF) 1-2 h post-intervention in humans ( 30- 32), suggesting that flavanols' indirect, vasodilatatory actions could account for acute cognitive enhancement following a single administration ( 16). Conversely, cognitive benefits associated with long-term flavonoids intake are more likely to involve morphological changes induced by direct actions on neuronal signaling. However, indirect mechanisms of action can also contribute to long-term neuroprotective effects, as increases in NO levels can further impact on brain vascularization over time by promoting angiogenesis, thus resulting in better cerebrovascular communication.

Effects of Cocoa Flavanols Daily Intake on Cognition: Evidence from Chronic Investigations

In line with the evidence suggesting a favorable association between flavonoids' regular consumption and cognitive performance in elderly subjects ( 33), chronic and sub-chronic cognitive effects of cocoa flavanols administration have been addressed in normal aging and clinical populations (see Table 1).

Table 1. Summary of the studies examining the effects of daily administration of cocoa flavanols on cognitive performance.

In this respect, the daily consumption of flavanol-rich cocoa drink has been showed to positively affect cognition, leading to improvements in cognitive performance both in older adults with early memory decline ( 36) and in cognitively intact elderly subjects ( 39). Specifically, compared to the low-flavanol condition (48 mg), the chronic administration of intermediate (520 mg) and high (993 mg) cocoa flavanols content over an 8-week period was associated to improvements in processing speed, executive function, and working memory in subjects with mild cognitive impairment. At higher cocoa flavanols concentrations, significant improvements were also evident in a verbal fluency task. Interestingly, such cognitive beneficial effects were paralleled by improvements in blood pressure and insulin resistance, suggesting a role of endothelial function and glucose sensitivity in modulating cognitive function in these patients ( 36). More recently, similar findings were replicated in healthy aged participants. Subjects in the intermediate and high cocoa flavanols groups, after a daily consumption over an 8-week period, showed better performance in several cognitive domains compared to those in the low-flavanol group ( 39).

By contrast, in healthy older adults a 6-week cocoa flavanols intervention showed no significant effects on cognitive and cardiovascular outcomes ( 34). In this study, however, participants were administered chocolate bar or beverage containing 397 or 357 mg flavanols, respectively; insufficient flavanols content may therefore account for the negative finding.

In middle-aged (40-65) subjects, Camfield et al. ( 35) investigated the chronic (30-day intake) neurocognitive effects of 250 and 500 mg cocoa flavanols administration using a spatial working memory task and steady-state visually evoked potentials (SSVEP). Compared to placebo, participants receiving cocoa flavanols treatment showed changes in SSVEP average amplitude and phase across several posterior parietal and centro-frontal sites that indicated an increased neural efficiency in response to the working memory task. Hence, cocoa flavanols long-term intake could effectively improve cognition trough increased neural efficiency, although, in this healthy population, the observed changes in brain activation were not paralleled by concomitant improvements in spatial working memory accuracy. Similarly, a sub-chronic (5 days) daily intake of 172 mg cocoa flavanols was associated, in healthy young subjects, to increased blood oxygenation level-dependent signal in various brain regions in response to an attention switching task, without any behavioral effect ( 31).

It has been proposed that cocoa long-term cognitive protection could particularly affect populations at risk. In this regard, Sorond et al. ( 37) evaluated the effect of flavanol-rich cocoa on neurovascular coupling in older subjects with vascular risk factors. In patients with impaired cerebrovascular coupling at baseline, cocoa administration was associated with improvements in cerebrovascular function both acutely and after a 30-day period. Moreover, chronic flavanols intake also resulted in improvements in cognitive flexibility. Conversely, no significant effects of cocoa administration on neurovascular coupling and cognitive performance were observed in those with intact cerebrovascular functions ( 37).

Besides improving CBF and CBF velocity after daily intake ( 41, 42), cocoa flavanols could also specifically affect cerebral blood volume in memory-related brain areas ( 38). Using high-resolution functional magnetic resonance imaging, a 3-month intervention with 900-mg cocoa flavanols resulted in increased cerebral blood volume in the dentate gyrus of the hippocampus, a structure particularly affected by aging and potentially implicated in memory decline. Moreover, the increase in cerebral blood volume was highly correlated with improvements in performance in a dentate gyrus-dependent memory task. Cocoa flavanols regular intake could therefore improve human dentate gyrus function through global increase in blood flow or a more selective increase in capillary density.

More recently, Neshatdoust et al. ( 40) investigated the link between cognitive performance and BDNF serum levels in older participants following cocoa flavanols chronic administration over 12 weeks. Results showed that, in comparison to a low-flavanol control (23 mg total flavanols), the daily intake of a high-flavanol cocoa drink (494 mg total flavanols) was associated with higher BDNF serum levels and improvements in global cognition scores. Therefore, changes in serum BDNF levels induced by cocoa flavanols could additionally underpin the beneficial effect of chronic cocoa flavanols intake on cognitive functions.

Collectively, these findings seem to support quite consolidated epidemiological evidence indicating that regular cocoa flavanols intake possesses the potential to protect human cognition, particularly in aged populations ( 33). As suggested ( 43), cocoa flavanols long-term beneficial effects on cognition could also possibly explain the correlation between country levels of chocolate consumption and Nobel Prizes per capita.

Acute Effects of Cocoa Flavanols Intake on Cognition

Only few randomized controlled trials have investigated the possibility that human cognitive function may be improved following acute cocoa consumption, within 6 h post-ingestion (see Table 2).

Table 2. Summary of the studies examining the effects of acute administration of cocoa flavanols on cognitive performance.

In a double-blind crossover study, 30 healthy adults were administered chocolate drinks containing 520 and 994 mg flavanols and 46 mg matched control, with a 3-day washout between sessions ( 44). Cognitive assessment, designed to be cognitively fatiguing, consisted in a 10-min task battery administered in six consecutive repetitions, including a serial subtraction task and a rapid visual information processing task. Results showed that, compared to control, both 520 and 994 mg cocoa flavanols doses significantly improved working memory performance on serial subtractions.

Using a similar acute intervention, Field et al. ( 45) found that 2 ho after a 773-mg cocoa flavanols supplementation, young participants showed enhanced performance on the accuracy measure of a spatial working memory task, as well as performance improvements on a choice reaction time task. Also, visual function was improved, with better visual contrast sensitivity and time to detect motion direction ( 45).

By contrast, Pase et al. ( 46) failed to demonstrate any acute effect of 500 mg cocoa flavanols administration on cognition in older adults. Cognitive assessment included measures of memory and attention. However, as a limitation, participants had a standardized lunch break before testing session; it is therefore possible that flavonoids effects were masked by post-prandial factors ( 46).

Immediate cognitive enhancement induced by high-flavanol cocoa is generally supposed to be mediated by the capability of their metabolites to promote crucial changes in peripheral and central blood flow. Some investigations therefore included behavioral and cardiovascular measures to explore the association between acute post-intervention cognitive enhancement and changes in peripheral and central blood perfusion. In this respect, Massee et al. ( 47) showed improvements in a serial subtraction task after the acute administration, in healthy subjects, of a cocoa bar containing 250 mg of flavanols. However, this study failed to demonstrate significant concomitant cardiovascular improvements after treatment. Conversely, a pilot study in healthy young participants showed that a single higher dose of flavanol-rich cocoa (516 mg) caused a significant global increase in CBF 2 h post-treatment ( 31). This result suggests an increased brain perfusion mediated by NO-dependent vasodilation, after cocoa consumption ( 31, 49).

In line with this result, in a recent near-infrared spectroscopy study, the administration of 903 mg cocoa flavanols increased cerebral oxygenation during the Stroop task performance in comparison to placebo, again suggesting increased NO-mediated vasodilation. Conversely, cocoa flavanols had no acute effects on serum BDNF levels ( 48). Therefore, these data support the idea that flavanols-induced acute changes in brain perfusion could underpin immediate cognitive-enhancing effects. However, the increased cerebral blood oxygenation was not paralleled by concomitant effects on cognitive performance ( 48). The young age of participants may have contributed to the lack of behavioral effects. This could be particularly relevant in this study, as participant performed a very short, relatively simple cognitive task. Since cocoa has been shown to affect cognitive performance in healthy individuals undergoing sustained effortful cognitive processing ( 44), these results open the possibility that, at least in healthy young adults, a high level of cognitive demand is needed to uncover the subtle immediate behavioral effects of flavonoids.

Accordingly, it could be argued that flavanols may be more effective in sustaining performance in highly demanding contexts or in presence of impaired physiological functions (e.g., cardiovascular risk factors). In this respect, we recently evaluated, in healthy young subjects, the effects of acute flavanol-rich chocolate administration on cardiovascular and cognitive function known to be specifically impaired by lack of sleep ( 27, 28). To this purpose, participants underwent two baseline sessions, performed after undisturbed nocturnal sleep, and two experimental sessions, after one night of total sleep deprivation. Subjects were randomly assigned to consume, 90 min before each testing session, flavonoid-rich dark chocolate (520 mg total flavanols) or flavonoid-poor chocolate (88.5 mg total flavanols). Cognitive assessment included the Psychomotor Vigilance Task, as a measure of behavioral alertness, and a 2-back working memory task. A single flavanol-rich cocoa administration was effective at counteracting the vascular impairment observed after a night of total sleep deprivation. Moreover, in the female subsample, cocoa flavanols also counteracted cognitive impairment specifically induced by sleep loss, leading to improvements in the accuracy measure of the working memory task. This result supports the idea of a specific effectiveness of cocoa flavanols in sustaining higher order cognitive performance during sustained effortful processing in healthy individuals. Interestingly, in the whole sample higher flow-mediated dilation levels, indicative of improved endothelial function, were related to better performance accuracy. Thus, although direct CBF measurements were not included, the results indicate that a single flavanol-rich chocolate administration could exert beneficial effects on cognitive performance through the capability to induce acute changes in peripheral and central blood flow via NO-dependent vasodilation.

Altogether, investigations on acute cognitive-enhancing effects of cocoa flavanols support the effectiveness of cocoa at sustaining cognitive performance, although with mixed results. Quantity and bioavailability of the consumed cocoa flavanols, together with the length and cognitive load of the cognitive assessment, represent crucial factors that may significantly impact on the experimental outcomes.

Conclusion

In recent years, in the context of an increased interest in the modulatory effects of food constituents on human health, cocoa flavanols have been suggested to display a variety of beneficial biological actions, including neuroprotection and cognitive modulation.

At present, the limited number of studies investigating cocoa flavanols intake and cognitive performance has produced mixed results. Indeed, physiological responses to flavonoid supplementation such as vasodilation, both at peripheral and central levels, have been consistently replicated; conversely, cognitive findings are not as unequivocal. When trying to account for such discrepancies, several methodological differences should be considered in dose, form, and timeframe of the cocoa flavanols administration, as well as in length and cognitive load of the experimental tasks. All these variables could have a remarkable impact on physiological and behavioral results and are likely to partly explain discrepancies among results.

Nevertheless, the evidence accumulated so far suggests that cocoa flavanols administration can be effective at sustaining cognitive performance, leading to improvements in measures of general cognition, attention, processing speed and memory. Beneficial cognitive effects of regular flavanols intake, particularly in patients at risk, are presumably mediated by direct neuroprotective actions as well as improvements in cerebrovascular and metabolic functions. Furthermore, acute administration of cocoa flavanols could result in immediate cognitive-enhancing effect, sustaining performance particularly in cognitively demanding conditions, including fatigue and sleep loss.

Altogether, research on the effects of cocoa and chocolate on human cognition, although at its preliminary stage, converges at pointing to cocoa as a new interesting nutraceutical tool to protect human cognition and counteract different types of cognitive decline, thus encouraging further investigations. Future research should be addressed to the identification of sensitive experimental measures capable of detecting flavanol-induced subtle changes in cognitive performance. Moreover, the characterization of appropriate dose, timing, and form of flavanols intervention required to reach beneficial effects in different populations, as well as the inclusion of fully matched placebo controls, are needed. Undefined remain also the effects of both acute and chronic administration of cocoa flavanols on chronic sleep deprivation and shift work, situations that may have a pronounced clinical impact. To elucidate immediate and long-term neuromodulatory properties of cocoa, future investigations should be ideally designed to include neuroimaging techniques in conjunction with cognitive and physiological measures.

Author Contributions

VS wrote the manuscript. VS and MF conceived and organized the structure of the review. DT contributed to write the first draft of the manuscript. DT, GD, LG, and MF contributed to the critical revision of the paper and approved the final manuscript for the publication.

Conflict of Interest Statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Abbreviations

BOLD, blood oxygenation level-dependent; BDNF, brain-derived neurotrophic factor; CBF, cerebral blood flow; ERK, extracellular signal-regulated kinase; LTP, long-term potentiation; MAPK, mitogen-activated protein kinase; NIRS, near-infrared spectroscopy; NO, nitric oxide; PI3-kinase/Akt, phosphoinositide 3-kinase; SSVEP, steady-state visually evoked potentials.

References

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Enhancing Human Cognition with Cocoa Flavonoids

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Enhancing cognitive abilities has become a fascinating scientific challenge, recently driven by the interest in preventing age-related cognitive decline and sustaining normal cognitive performance in response to cognitively demanding environments. In recent years, cocoa and cocoa-derived products, as a rich source of flavonoids, mainly the flavanols sub-class, have been clearly shown to exert cardiovascular benefits.

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https://theconversation.com/research-check-does-eating-chocolate-improve-your-brain-function-55229

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Everyone loves a study that turns one of our favourite vices into a health benefit. This week, the news headlines tell us "eating chocolate improves brain function" and that it "could help protect against normal age-related decline".

The study, published this month in the peer-reviewed journal Appetite, found that memory and abstract thinking improved in those reporting more chocolate consumption. These effects were reported not to be influenced by factors such as age, weight and general health measures.

Before you reach for a Mars bar or a Dairy Milk, let's take a step back.

This is a correlational study. That means it shows an association between people who reported regularly eating chocolate and better scores on brain function tests. It doesn't show that chocolate consumption directly improves brain function.

Other factors are also at play. The people who consumed more chocolate also had better diets and drank less alcohol. And both groups relied on their memory to report their chocolate consumption levels.

Sorry, folks, but you won't be able to rely on this study to justify your 3pm chocolate binge.

How was the study conducted?

The 968 participants were from the Maine-Syracuse Longitudinal Study, which has followed the same group of New Yorkers for more than 35 years. The participants undertake questionnaires and physical examinations at various intervals so researchers can determine changes associated with ageing, the development of heart disease and also cognitive performance.

In 2006, the participants reported how often during the week they ate a variety of foods, including chocolate, meat, eggs, breads, rice, fruit, vegetables, dairy, nuts and beverages such as tea, coffee, water, fruit juice and alcohol. Chocolate was not differentiated according to whether it was dark, milk or white chocolate.

The researchers compared those who never or rarely ate chocolate (337 people) and those who ate chocolate at least once a week (631 people).

Participants were given various brain function tests - including remembering where things were (spatial memory), abstract reasoning, working memory and attention. The relationships between chocolate intake and performance on the cognitive tasks were then analysed.

The results from people who had dementia were excluded, as this is a serious cognitive impairment, as were people who had experienced a stroke, as this would skew the results.

What were the results?

The participants reporting that they ate chocolate more than once a week performed better in most of the cognitive tests, particularly on their "visual-spatial memory and organisation" score. There was no relationship with working memory.

More women were self-reported chocolate eaters, so this could bias the results. Women often perform better than men in certain tests of cognitive function, particularly in the elderly.

The chocolate-eating group was less likely to have high blood pressure or diabetes and had lower fasting blood glucose levels (indicative of pre-diabetes) than non-chocolate-eating participants.

However, chocolate eaters had higher cholesterol, including low-density lipoprotein (bad) cholesterol, which is associated with poorer cardiovascular health.

So what does it all mean?

Chocolate is often demonised due to the high sugar and fat content in chocolate bars and its association with "guilty pleasure". But cocoa (or chocolate in its raw form) actually contains lots of compounds that act in the brain.

In particular, cocoa contains flavanoids, which are found in fruits such as grapes and apples. Cocoa also contains caffeine and theobromine, which are the stimulants found in coffee and tea. These natural compounds are thought to improve alertness and so can improve brain function.

But the amounts of these chemicals depend on the cocoa concentration of chocolate - milk chocolate contains much less of these active ingredients than dark chocolate. The study points out that the type of chocolate consumed wasn't assessed, so we don't know whether this had an impact on the results.

It's important to remember that this is a correlational study. It doesn't examine whether chocolate consumption directly improves brain function. To test this, an experiment would ask people to eat a chocolate-rich diet or a no-chocolate diet for a reasonable amount of time, and then carry out the brain function tests. This would be a way of establishing whether chocolate can enhance cognitive performance.

What else do we need to take into account?

The participants who consumed chocolate also reported eating more serves of vegetables, meats and dairy foods, and more food overall, as well as drinking less alcohol. This indicates they may have had better diets overall, regardless of their reports of eating more chocolate.

Alcohol intake is known to diminish brain function, so could have an impact on the non-chocolate-eating group. The authors followed up this observation by examining alcohol intake separately and found no association between alcohol intake and the tests of brain function. This suggests that alcohol didn't have an impact on brain functions measured. However, it could indicate differences in general health and well-being.

More people in the non-chocolate-eating group had diabetes, so they may have been avoiding chocolate because of the high sugar content. Diabetes has been linked with cognitive impairments, particularly in memory performance, so this could affect the results.

Another issue is that the participants were retrospectively self-reporting their food intake in response to a questionnaire. People can easily misreport or underestimate their consumption.

(In fact, the lower scores on the brain function tests by people who consumed less chocolate could reflect a group that was less able to accurately report their food consumption. Asking someone to recall their food for the week is a test of memory in itself!)

Portion sizes weren't reported either, only the frequency of foods eaten over days. So the research didn't differentiate between whether you eat a family-sized bar of chocolate, or just a single square.

This type of cross-sectional study is great for showing the relationship between diet and health at a snapshot in time. But correlation does not equal causation. To really get to the bottom of this issue, we need carefully designed experimental studies to examine the association between chocolate and cognitive health, and the mechanisms linking them. - Amy Reichelt

Peer review

This review of the article is a sound interpretation of the results.

The important point is that although the participants were in a longitudinal study that recruited people in waves between 1975 and 2000, the measurement of dietary intake and the cognitive function testing was only done on a sub-group who came in for testing during the sixth wave of follow-up, between 2001 and 2006. So the main analysis could only look at cross-sectional associations.

The participants were divided into three groups based on usual chocolate consumption: never, once a week, or more than once a week. But it's not clear whether usual intake was over the past year, or just for the past week, which could affect the results.

The review clearly highlights some other potential explanations for the findings, including that those who ate chocolate also reported some healthier eating patterns. It's very likely that those with diabetes would have been advised to eat less chocolate.

The observation of a lower proportion of chocolate eaters having high blood pressure is consistent with a systematic review showing that regular chocolate consumption can have a small blood-pressure-lowering effect.

However, as much as we would all love the results of the cross-sectional analysis to be true, a 2013 systematic review found that, in trials lasting between five days to six weeks, chocolate did not improve cognitive function.

I agree with the conclusion that better-quality trials, including mechanistic studies, are needed. - Clare Collins

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Research Check: does eating chocolate improve your brain function?

# data[].attributes.attachment_link.description
Everyone loves a study that turns one of our favourite vices into a health benefit. This week, the news headlines tell us "eating chocolate improves brain function" and that it "could help protect against normal age-related decline". The study, published this month in the peer-reviewed journal Appetite, found that memory and abstract thinking improved in those reporting more chocolate consumption.

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We decided to choose this topic because it interested us in how specific types of chocolate can affect your brain's abilities to focus and overall improves cognitive performance. We wanted to relate this more specifically to students and school activities so our question specifically focuses on the type of chocolate you eat compared to how long you are able to study for typically on a test. We correlated that the longer someone studies, the more focus they hold. We will go about getting the best information about this by conducting a survey through google form that will be sent out to the students of 10th grade.

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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6262453/

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Abstract

Dark chocolate is rich in flavonoids that can have effects on body composition and cognitive performance. The aim of this study was to analyze the effects of acute and subchronic chocolate intake on electrical brain oscillations. A study with 20 healthy subjects (mean age of 24.15 years) and a control group with five subjects (mean age of 23.2 years) was carried out. In the acute effect study, the subjects' intake was dark chocolate (103.72 mg/kg of body weight) rich in flavonoids and low in calories as in fasting. In the control group, the subjects intake was only low-calorie milk. For the subchronic effect, a daily dose of dark chocolate was given for eight days. The baseline electroencephalogram (EEG) was recorded before dark chocolate intake; at 30 min, the second EEG was carried out; on the eighth day, the third and fourth EEGs were performed before and after the last intake. In acute and subchronic intake, Delta Absolute Power (AP) decrease was observed in most brain regions ( p < 0.05), except in the right fronto-centro-temporal regions. In the Theta band, there was a generalized decrease of the AP of predominance in the left fronto-centro-temporal regions. In contrast, an increase in AP was observed in the temporo-occipital regions in the Alpha band, and in the right temporal and parieto-occipital regions in the Beta band. The control group did not have significant changes in brain oscillations ( p > 0.05). We concluded that acute and subchronic chocolate intake decreased the Delta and Theta AP and increased Alpha and Beta AP in most brain regions.

Keywords: dark chocolate, electroencephalogram, cognitive effects

1. Introduction

In recent years, one of the major problems of global public health has been the growth of the population over 65 years old, and the increase in aging-related diseases such as mild cognitive impairment and dementias [ 1]. On the other hand, in the first years of life, increases in the availability of neonatal intensive care units have resulted in an increase in the number of surviving premature and very-low-birth-weight infants with perinatal brain injury (PBI) [ 2]. Therefore, one of the current scientific challenges in these two population groups is to modify aging and to prevent and eventually reverse cognitive impairment or enhance cognitive performance [ 3]. Thus, the chronic intake of flavonoids has been demonstrated to have beneficial effects for cardiovascular disease and many others, which include decreasing blood pressure in hypertensive patients, and decreasing insulin resistance and overweight in patients with metabolic syndrome. Chocolate, especially dark chocolate with its high content of flavonoids and theobromine, has proven to be a promising food for cardiovascular and metabolic effects [ 4].

Recently, some papers have shown that the flavonoids of dark chocolate improve cognitive functions, specifically working on memory and Trail-Making-Tests in healthy people and those with cognitive impairment [ 5, 6]. Dark chocolate has the highest flavonoid content. Some commercial preparations have modified the composition of dark chocolate to increase the flavonoid content and decrease the caloric intake. Analysis of the effects of dark chocolate has been divided according to the days in which it is ingested in acute, subchronic and chronic conditions [ 7].

Although some effects of dark chocolate on cognitive performance have already been studied, research on the modifications of brain electrical activity after the acute intake of chocolate has been poorly analyzed. It is well established that by taking advantage of such powerful electroencephalographic (EEG) technology one could easily probe brain electrical oscillations. With the use of quantitative EEG (qEEG) for the analysis of brain electric activity, precision and consistency were improved [ 8, 9, 10]. Currently, to our knowledge, there are no papers that study the acute effect of dark chocolate on brain electric oscillations in healthy people. Therefore, the objective of our study was to analyze how brain oscillations are affected by the acute intake of chocolate rich in flavonoids and low in calories, as well as the intake of one cup of chocolate every morning for seven days.

2. Materials and Methods

A prospective longitudinal study was conducted. Twenty healthy subjects (13 female and 7 male), volunteers, who attended the specialized center (Diagnóstico, Tratamiento e Investigación Neurológica, S.C.) were included in groups of five people every two weeks to complete the 20 subjects. The control group included 5 healthy subjects (3 female and 2 male). Subjects in the study group ingested low-calorie milk with dark chocolate, while the control group ingested only low-calorie milk. Characteristics of the study were fully explained to each participant, as well as the minimum risks of participating in the project; those who agreed signed an informed consent form, and underwent clinical nutritional and neurological examinations. The project followed the Helsinki guidelines and was approved by Ethical Research Committee of Diagnóstico, Tratamiento e Investigación Neurológica, S.C. (protocol # 2016/001; date of approval: 28 November 2016).

2.1. Baseline EEG Recording

The baseline EEG was recorded over twenty minutes; patients closed their eyes but stayed awake during the procedure, and the data were collected using the Medicid-5 system (Neuronic Mexicana, SA, México City, México). Amplifier characteristics were as follows: 10,000 dB gain, low-cut filters at 0.05 Hz and high-cut filters at 70 Hz. Nineteen referential leads of the International 10/20 System with linked earlobes as references were used ( Figure 1 ). The impedance was under 5 Kohms in all electrodes with a sampling frequency of 200 Hz. All EEG recordings were analyzed by clinic neurophysiologists (ES-R). The analysis of background EEG activity was carried out with the Fast Fourier Transform. Twenty-four segments of 2.56 s each were selected in blind form by the principal author (ES-R). Only the segments in which the patient was totally awake were analyzed to obtain the absolute power (AP), relative power (RP) and mean frequency (MF) of Delta (0.5-3.5 Hz), Theta (3.6-7.5 Hz), Alpha (7.6-12.5 Hz) and Beta (12.6-19 Hz) bands. The subtraction of the global scale factor (GSF) was applied to AP in all bands to decrease non-physiological variability; this procedure is known to improve diagnostic precision [ 11].

2.2. Experimental Maneuver

The experimental maneuver consisted of ingesting 6.8 g of dark chocolate rich in flavonoids (375 mg) and low in calories (25 kcal) CocoaVia (Mars Symbioscience Inc., Germantown, MD, USA) dissolved in 250 mL of low-calorie milk (115 kcal, Milk and Derivatives Trader, SA CV, Torreón, México). Subjects in the control group only ingested 250 mL of low-calorie milk. After thirty minutes of chocolate intake or low-calorie milk, the second EEG was performed with the same characteristics as the baseline EEG recording. For the subchronic effect, a daily dose of dark chocolate was given for eight days, and the third EEG was performed after the last intake on day eight.

2.3. Statistical Mnalysis

Statistical analysis was performed using descriptive measures, mean and standard deviation. For the analysis of brain electrical activity, the baseline values of AP and MF of Delta, Theta, Alpha and Beta bands were normalized to 100%, and the percentage of variation after dark chocolate intake was comparable among all subjects. Both crude and normalized values were compared by means of a one-way repeated measures ANOVA, and two conditions (before and after dark chocolate intake) were used for analyses in Neuronic Statistics (Neuronic Mexicana, SA, México City, México, 2011), a specialized statistical program for EEG analysis. Values of p < 0.05 were considered significant.

3. Results

In the chocolate group we studied 20 healthy subjects; 7 males and 13 females, and the subjects had a mean age of 24.15 ± 4.84 years. Subjects were free of metabolic and nervous system diseases, although two of them were overweight (body mass index of 32.1 and 35.4). In the control group, 5 healthy subjects with a mean age of 23.2 ± 2.58 years were studied (3 female and 2 male). The results of the effect of chocolate intake or low-calorie milk on brain electrical activity are described in the next paragraphs.

3.1. Acute Effect of Dark Chocolate Intake

Modifications of brain electrical activity after intake of 250 mL (103.72 mg/kg of body weight) of dark chocolate were observed in AP and MF in various leads and in different frequency bands ( Table 1 ). Delta AP decrease was observed in most brain regions ( p < 0.05, n = 20, ANOVA-test), except in the right fronto-centro-temporal regions, where there were no significant changes. Additionally, in the Theta band, there was a generalized decrease in the AP of predominance in the left fronto-centro-temporal regions. In contrast, in the Alpha and Beta bands, an increase in AP was observed. In the Alpha band, this increase was localized in the temporo-occipital regions, and in the Beta band, this increase was localized in the right temporal and parieto-occipital regions in bilateral form ( Figure 2 ). The most significant values were observed in the occipital leads, and the Alpha and Beta bands are described in detail in the following paragraphs. The baseline Alpha AP of the O1-AVR lead was 49.68 ± 51.71 μV2/Hz after the chocolate intake was increased by 32.69% ( p = 0.04). The Alpha AP of the O2-AVR lead was 62.12 μV2/Hz; after ingesting the chocolate, an increase of 29.01% was observed ( p = 0.009). The baseline Beta AP of the O1-AVR lead was 4.50 ± 1.85 μV2/Hz, and post-chocolate intake increased by 26.33% ( p = 0.0001). In the O2-AVR lead, baseline was ±2.14 μV2/Hz, and a significant increase of 17.21% ( p = 0.0001) was observed after chocolate intake ( Figure 3 and Figure 4 ).

Table 1

Leads

AP Delta

AP Theta

AP Alpha

AP Beta

3.2. Acute Effect of Low-Calorie Milk Intake

After the ingestion of 250 mL of low-calorie milk, no significant differences were observed between the baseline values of the AP of the Delta, Theta, Alpha and Beta bands in any of the brain regions analyzed ( p > 0.05, n = 5, ANOVA-test). In contrast to the chocolate group, in the control group the alpha and beta AP did not change significantly in the occipital regions. The baseline Alpha AP of the O1-AVR lead was 38.20 ± 8.49 μV2/Hz after the low-calorie milk intake was 39.40 ± 13.25 μV2/Hz ( p = 0.73). The Alpha AP of the O2-AVR lead was 48.68 μV2/Hz; after ingesting the low-calorie milk was 42.84 ± 23.00 μV2/Hz ( p = 0.18). The baseline Beta AP of the O1-AVR lead was 4.72 ± 2.73 μV2/Hz; after ingesting the low-calorie milk was 4.39 ± 2.03 μV2/Hz ( p = 0.40). In the O2-AVR lead, baseline was 4.24 ± 1.78 μV2/Hz, and a non-significant decrease to 3.81 ± 1.28 μV2/Hz ( p = 0.16) was observed after low-calorie milk intake ( Figure 3 and Figure 4 ).

3.3. Subchronic Effect of Seven-Day Dark Chocolate Intake

To evaluate the subchronic effect of daily chocolate intake, the baseline AP value in the O1 and O2 leads was compared with those obtained seven days later. In the O1-AVR lead, the Alpha AP increased to 63.39 ± 58.23 μV2/Hz, which represented 30.51% ( p = 0.007). The AP Alpha of the O2-AVR lead increased to 72.85 + 65.13 μV2/Hz with an increase of 49.52% ( p = 0.023). Finally, the Beta AP of the O1-AVR lead increased to 5.16 ± 1.69 μV2/Hz, representing 19.0.2% ( p = 0.005). In the O2-AVR lead, the increase was 5.65 ± 2.87 μV2/Hz, representing 28.09% ( p = 0.03) ( Figure 3 and Figure 4 ).

3.4. Acute Effect on a Subchronic Effect of Dark Chocolate Intake

The Alpha AP of the O1-AVR lead increased to 71.23 ± 61.36 μV2/Hz, corresponding to 54.01% ( p = 0.0003). In the O2-AVR lead, the AP increased to 78.12 ± 61.51 μV2/Hz, corresponding to 71.88% ( p = 0.007). Finally, the Beta AP of the O1-AVR increased to 6.12 ± 2.13 μV2/Hz, corresponding to 40% ( p = 0.000009). In the O2-AVR lead, the AP increased to 6.62 + 3.55 μV2/Hz, corresponding to 47.28% ( p = 0.004) ( Figure 3 and Figure 4 ). On day eight, after the last chocolate intake, the increase in Alpha and Beta AP was higher than basal AP and the AP after seven days of intake.

3.5. Modifications of Mean Frequency

After dark chocolate intake, no modifications in MF Delta, Theta, and Beta were observed. Only a generalized decrease of MF Alpha was observed, with more significant values in occipital regions ( Figure 2 ). In spectral analysis of EEG, the characteristic Alpha spectral peak was moved to lower frequencies in the majority of subjects, and this modification was more evident at seven days, and after the last dark chocolate intake at day eight. In less consistent form, an increase in the amplitude of the spectral Alpha peak was found.

4. Discussion

The main results of our study were that intake of 6.8 g of dark chocolate is enough to cause a decrease in the AP Delta and Theta, and an increase in the AP Alpha and Beta in the temporo-occipital leads without changes of brain oscillations in the control group. In addition, a decrease in MF Alpha was found. These results will be analyzed in the following paragraphs.

Chocolate, especially dark chocolate, with its high content of flavonoids, has proven to be a promising food in terms of its cardiovascular effects. Recently, some studies have reported cognitive effects after intake of dark chocolate, specifically on attention and working memory. To date, only one study has reported the effects of dark chocolate on brain electrical activity, specifically stable-state visual evoked potentials [ 12]. Moreover, no study has reported the effects of chocolate on human brain electrical oscillations recorded in the EEG. In our study, we analyzed the acute effect of the intake of a single dose of dark chocolate and the subchronic effect of daily intake for seven and eight days.

In the acute effect analysis, there were notable changes in brain electrical activity 30 min after dark chocolate intake without changes of brain oscillations in the control group. It has been postulated that the cognitive acute effects appear a few minutes after dark chocolate intake and can be mediated indirectly by vascular mechanisms that cause an increase in cerebral blood flow. In recent studies, it was shown that dark chocolate intake with a mean dose of 516 mg and a high dose of 903 mg of flavonoids increases brain blood flow as evaluated by functional magnetic resonance [ 13] and near-infrared spectroscopy [ 14]. However, these studies show conflicting results if the increase in cerebral blood flow is mediated by nitric oxide-induced vasodilation or not. Regarding the cognitive effects of chocolate intake, a double-blind crossover study of three groups was conducted: the first with high-dose flavonoids (994 mg), the second with 520 mg, and a control group with 46 mg. A working memory task of serial digital subtraction before and after the intake of chocolate was applied. Subjects with medium and high doses of flavonoids showed significant improvement in this work memory task in relation to the control group [ 15]. Other studies have had similar results [ 16], and negative results [ 17]. On the other hand, the effects found with dark chocolate could be attributed to the low-calorie milk in which the chocolate was dissolved. However, in the control group where the subjects ingested the same amount of low-calories milk but without dark chocolate, no significant changes in the brain oscillations were observed.

On the other hand, the acute effect of dark chocolate intake seems to have a direct relationship with the demand for cognitive resources of the task or with the interference or damage of the neural circuits involved in the task. This was observed in the study by Grassi et al. [ 18], in which the dark chocolate effect was compared in a group of subjects with sleep deprivation and a control group with normal sleep submitted to a working memory 2-back test. The results showed that the intake of a single dose of chocolate reversed the deleterious effects of sleep deprivation and even improved performance of tasks on the basal level. Consistent with previous results, in our study, the highest increases in Alpha and Beta AP were observed in those subjects with the lowest values at baseline. Therefore, in future studies, it would be desirable to evaluate whether similar doses of dark chocolate flavonoids produce different effects in populations of healthy subjects, with cognitive impairment and learning or neurodevelopmental disorders.

In addition to vascular changes and cerebral blood flow, it is possible that dark chocolate effects occur through neural networks involved in the processes of attention, work memory or episodic memory, and that these effects can be acute or subchronic. Flavonoids cross effectively the blood brain barrier, and many studies have found them in brain regions that are actively involved in the processes of attention, episodic, procedural and working memory, such as the hippocampus, frontal cortex and basal ganglia [ 19]. In an experimental study, the authors analyzed whether epicatechin, a dark chocolate flavonoid, could enhance memory formation of Lymnaea snail exposed to epicatechin before training, during the consolidation period immediately following training and 1 hour after training. Only the snails exposed to epicatechin immediately after training showed enhanced memory formation [ 20]. In addition, in a mouse experimental model, the effects of the chronic consumption of food enriched in cocoa-based dark chocolate on the excitability of hippocampal neuronal networks were analyzed. A significant enhancement in seizure-like population spike bursting at the neurogenic dentate gyrus was found with a reduction in the levels of GABA-α1 receptors [ 21].

It is necessary to emphasize that in our study, although the effects of dark chocolate on electrical brain activity were recorded in almost all brain regions, they were more evident in the temporo-occipital regions for the Alpha band, and in the parieto-occipital and temporal regions in the Beta band. In these regions, the neural circuits are actively involved in visuospatial working memory and episodic memory processes. In addition, the Alpha frequencies have been implicated in visuospatial working memory processes especially in the maintenance phase, where it has been observed that the higher the complexity of the task and the greater the demand for cognitive resources, the Alpha spectral peak has a greater amplitude, indicating that a greater number of neurons are activated synchronously [ 22, 23, 24].

Our study has some limitations; for example, the sample size was small, especially in the control group; however, it was sufficient to detect changes in brain electrical oscillations in chocolate-ingesting groups.

5. Conclusions

We can conclude that the results of our study sustain that acute and subacute dark chocolate intake decreases the AP of the Delta and Theta bands, and increases the AP of the Alpha and Beta bands in most brain regions, especially in the temporo-occipital leads. The control group, with low-calorie milk intake, did not have significant changes in brain oscillations.

Acknowledgments

We appreciate the participation in the study of all voluntary subjects.

Author Contributions

Conceptualization, E.S.-R., B.E.-Z. and E.Z.-U.; methodology, E.S.-R., B.E.-Z. and E.Z.-U.; software, B.E.-Z. and E.Z.-U.; formal analysis, E.S.-R., B.E.-Z. and E.Z.-U.; investigation, E.S.-R., B.E.-Z. and E.Z.-U.; resources and data curation, B.E.-Z. and E.Z.-U.; writing-original draft preparation, E.S.-R. and B.E.-Z.; writing-review and editing, E.S.-R., B.E.-Z. and E.Z.-U.; visualization and supervision, E.S.-R.; project administration, E.Z.-U.

Funding

This research received no external funding.

Conflicts of Interest

The authors declare no conflicts of interest.

Articles from Foods are provided here courtesy of Multidisciplinary Digital Publishing Institute (MDPI)

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Effects of Dark Chocolate Intake on Brain Electrical Oscillations in Healthy People

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Dark chocolate is rich in flavonoids that can have effects on body composition and cognitive performance. The aim of this study was to analyze the effects of acute and subchronic chocolate intake on electrical brain oscillations. A study with 20 healthy ...

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Source: Enhancing Human Cognition with Cocoa Flavonoids 

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Source: Enhancing Human Cognition with Cocoa Flavonoids 

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Pro-
This source includes a summary of the studies examining the effects of daily administration of cocoa flavanols on cognitive performance. It includes a large range of participants and the different flavanol amounts, and discusses their findings through their statistical study. This information would lead readers to the same conclusion because it shows evidence as to how chocolate improves cognitive function.
Counter-
It does not focus on a specific type of chocolate and also doesn't have a wide variety of different types which may stray readers from agreeing with their conclusion. The chocolate used in their experiment is not very specified and varies only from chocolate bar to cocoa supplements and drinks which could cause different results.

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Source: Can Chocolate Make You Smarter? 

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Source: Can Chocolate Make You Smarter? 

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#1: This source could have specified more about their statistical study and not left it to be so vague. It is important to know how many people out of the 1000 participants performance increased or some sort of percentages could have been useful so that we can have a better understanding on the results.

#2: It would be beneficial to compare the results between students (younger people) versus the adults that were only studied in this experiment because it gives us a larger variety of answers that could potentially prove something about the age factor as well.

#3: Having a larger sample size would always improve the accuracy of ones study.

#4: The experiment did not take account the types of chocolate people had and simply asked people how often they ate chocolate which could possibly be too vague to receive accurate statistical answers.

#5: Adding a graph or data table with the factors and results of this study would be extremely useful in comparing the results and discussing this topic instead of just writing about the results with no specific percentages or visuals.

#6: The rules and restrictions of their experiment could definitely be more defined and clear so that they would have a better perspective on this topic. For example they mentioned how they did not take into account how much chocolate people ate, only how often. They also mentioned how this study was cross-sectional only.

#7 Adding on to the previous criticism, something that is very small but could definitely be a significant factor is what would be considered eating chocolate in this study. Is it if a participant eats only a chocolate bar or are foods that include some chocolate like ice cream or cookies also counted towards chocolate consumption. More specifically its unclear how much chocolate you have to eat in order for it to count.

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Source: Research Check: does eating chocolate improve your brain function?

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Source: Research Check: does eating chocolate improve your brain function?

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Pro: This source discussed a certain study where they tracked the type of food people ate for a week and wanted to see if the people who consumed more chocolate did better cognitively. Their use of statistics leads the reader to the same conclusion because it provides specific information about their study and their results matched with their hypothesis on what they believed would happen.

Counter: This source mentions while discussing the results that the answers could potentially be biased because there were more women who ate chocolate and according to their research, women often perform better than men in certain tests of cognitive function.