Coffee, caffeine and health

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Expert comment by Dr Astrid Nehlig

In January, the European Food Safety Authority published its anticipated draft scientific opinion on the use of health claims relating to caffeine. Drawing on the available body of scientific research, it was concluded that single doses of caffeine up to 200mg and daily intakes of up to 400mg do not raise safety concerns for adults in Europe. Below I provide an overview of some of the latest research in this area.

Alertness
The caffeine in coffee is probably most well-known for its stimulating effects, which research has proven benefits mental performance – including improving visual attention, memory performance and alertness.

The effect of caffeine on alertness is most marked in situations where an individual’s alertness level is reduced. During night work, for example, caffeine has been found to reduce cognitive failures and accidents in subjects consuming over 200mg caffeine daily1. Caffeinated coffee and a short nap have also been shown to be the most effective ways to counteract driver fatigue2.

Although caffeine has been found to restore wakefulness and counteract the decline in mental performance due to lack of sleep, it may also have a detrimental effect on sleep quality in some individuals.

Some people who are particularly sensitive to caffeine may take longer to fall asleep, their duration of total sleep and deep sleep will be reduced and they will experience more frequent awakenings. These effects are usually less marked in regular consumers, and caffeine abstinence can also improve these symptoms.

Sports performance
In exercise the effects of caffeine are not so clear cut. In short-term, high intensity exercise caffeine has inconclusive effects; with long-term endurance exercise EFSA has established a causal relationship between caffeine intake and endurance capacity, and performance and the rate of perceived performance.

Caffeine has also been found to moderate central fatigue and influence ratings of perceived exertion, pain and levels of vigour – all of which are likely to lead to improvements in performance3.

Fluid balance
There are widespread guidelines on the amount and types of fluid we should be drinking in order to remain well hydrated, particularly during physical activity, and we hear a lot about how individuals should avoid caffeinated beverages in order to stay well hydrated.

Whilst caffeine is a mild diuretic agent which increases the frequency of urination, it does not increase the amount of fluid passed, and the benefits that can come from the fluid intake from caffeinated beverages outweigh the potential mild diuretic effect of caffeine.

Scientific evidence looking at the effects of caffeine on fluid balance does not support the hypothesis that caffeine has a significant diuretic effect4. Furthermore, coffee drinking in moderation contributes to our daily fluid intake and does not lead to dehydration, or a significant loss in body fluid5,6.

Dependence
The issue of possible dependence on caffeine is something that we also see continuously debated. While caffeine in coffee is a mild central nervous system stimulant, scientific studies using brain scans, such as De Luca M.A. et al in 20077, suggest that moderate coffee drinkers do not develop a physical dependence to caffeine.

However it is true that the American Psychiatric Association has added caffeine withdrawal to the symptoms8 that it recognises. It is known that some people may experience symptoms after the abrupt cessation of caffeine; research suggests this occurs 12-24 hours after cessation of caffeine and translates into headaches, drowsiness, and feeling of fatigue, but won’t last more than 48 hours and can avoided by the progressive decrease of intake.

Taken overall, the evidence to date does suggest that people can continue to enjoy moderate caffeine consumption as part of a healthy, balanced diet.

References
1. Smith A.P. (2005) Caffeine at work. Hum Psychopharmacol, 20:441-5
2. Reyner L.A. & Horne J.A. (1997) Suppression of sleepiness in drivers: combination of caffeine with a short nap. Psychophysiology, 34:721
3. Davis J.K. et al. (2009) Caffeine and anearobic performance: ergogenic value and mechanisms of action. Sports Med, 39:813-32
4. Popkin B.M. et al. (2006) A new proposed guidance system for beverage consumption in the United States. Am J Clin Nutr, 83:529-542
5. Kolasa K.M. et al. (2009) Hydration and health promotion. Nutrition Today, 44:190-203
6. Killer S.C. et al. (2014) No Evidence of Dehydration with Moderate Daily Coffee Intake: A Counterbalanced Cross-Over Study in a Free-Living Population. PLoS ONE, 9(1):e84154
7. De Luca M.A. et al (2007) Caffeine and accumbens shell dopamine. J Neurochem 103:157-163
8. American Psychiatric Association (2013) Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM V) ISBN 978-0-89042-554-1DSMV

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