IFIC
REVIEW
International Food Information Council Foundation
Caffeine & Health:
Clarifying The Controversies
MENTAL PERFORMANCE
It has long been anecdotally reported that caffeine has the ability to improve alertness and aid in concentration. Recent studies in a number of laboratories have consistently demonstrated increases in key aspects of cognitive function related to alertness, even among well-rested volunteers. Additionally, caffeine enhances self-rated moods such as vigor, efficiency, energy and clear-headedness. These effects are present at consumption levels as low as 32mg (less than an eight-ounce cup of hot tea). [Lieberman, 2001]
Additionally, a study at the French National Institute for Health and Medical Research in Montpellier, France showed that consumption of at least three cups of coffee per day is associated with a slower rate of decline in cognitive abilities in women. Caffeine, which has already been associated with increased mental performance, has been identified as the ingredient most likely contributing to these results. These beneficial effects on cognitive decline in women appear to increase with age. [Rithcie, et al., 2007]
Although there have been reports of caffeine causing anxiety, a number of reviews of the research have shown that only extremely high levels of caffeine bring on anxiety (1,000-2,000 mg caffeine per day), and even this has not been shown to be consistent among reviews. [Smith, 2002; Stern, et al. 1989] Anxiety is rarely seen within the average range of caffeine consumption.
While large amounts of caffeine late in the evening may interfere with the onset of sleep, consumption at least eight hours prior to sleep will not affect sleep onset. [Smith, 2002; Bonnet, et al., 2005] Teenagers tend to stay awake longer as the school-week progresses, gradually becoming more sleep-deprived, and may consume caffeine to counteract daytime sleepiness. [Pollack and Bright, 2003] In practice, those experiencing sleeplessness learn to moderate caffeine consumption to levels and time of day that are more acceptable to them. [Smith, 2002; Nawrot, et al., 2003] Furthermore, with regular consumption of caffeine, tolerance to some of its effects can result, reducing the severity of those effects. [Bonnet, et al., 2005] Although not well documented, researchers have suggested that the familiar caffeine “morning pick-me-up” may simply be the relief of overnight withdrawal symptoms. [Dews, et al., 2002; British Nutrition Foundation, 2007]
Research has also shown that sleep-deprived individuals consuming caffeine had improved memory and reasoning. [Lieberman, 2001] Alertness and performance also improve at levels of 75-150mg after acute restriction of sleep, and at intakes of 200-600mg after one or more nights without sleep. [Bonnet, et al., 2005]
PHYSICAL PERFORMANCE
In addition to its effects on mental performance and mood, evidence has also shown that physical performance may be improved following caffeine consumption. [Magkos and Kavouras, 2004] Also, caffeine in amounts greater than 220mg has been found to significantly improve performance in simulations of driving and industrial work. [Smith, 2005]
Consuming 6mg/kg body weight of caffeine, or about five 8-ounce cups of coffee for a 155lb. male, significantly increased muscle endurance during brief, intense exercise (4-6 min) performed by recreational athletes. [Jackman, et al., 1996] In addition, Bruce et al. (2000) reported that intake of 6 or 9 mg/kg of caffeine, or about five or seven 8-ounce cups of coffee, respectively, produced a significantly improvement in performance compared with a placebo for competitive male rowers during a 2,000-meter time trial. Notably, the lower dose of caffeine (6mg/kg) resulted in the fastest performance times. Caffeine ingestion of 5mg/kg prior to a maximum effort run resulted in significantly greater anaerobic metabolism and performance among recreational runners. [Doherty, 1998] Similarly, healthy untrained subjects performing a maximal oxygen deficit cycling test had significantly improved endurance following ingestion of 5 mg/kg caffeine. [Bell, et al., 2001] One of the few caffeine studies utilizing female subjects found that 6 or 9 mg/kg caffeine (about four or six 8-ounce cups of coffee for a 132 lb. female, respectively) produced dose-dependent improvements during repeated 2,000-meter time trials among competitive oars-women. [Anderson, et al., 2000]
In another study on cyclists, moderate levels of caffeine (6mg/kg) enhanced the performance times during a cycling trial. [Cox, et al., 2002] This result was observed whether caffeine was ingested on hour before exercise or in a series of administrations throughout the trial. The researchers also found support for the observed practice of consuming commercial soft drinks as a replacement for sport drinks during the last part of an endurance event. In a double-blind study, soft drinks produced enhanced performance at the end of the task, with the benefits being largely due to the ingestion of a small amount of caffeine (1.5mg/kg). Direct comparison of the ingestion of larger amounts of soft drink suggests that all types of caffeinated beverages, including soft drinks and sports drinks, are of equal and worthwhile benefit to the performance of a prolonged cycling task.
Consumption of caffeine prior to exercise has been shown to improve endurance during physical exercise. One suggested explanation for this was that caffeine enhanced fat utilization during exercise, instead of burning muscle; however, Laurent et al. (2000) showed that this was not the case. Rather, caffeine may lower the threshold for exercise-induced β-endorphin and cortisol release, hormones that produce the so-called “runner’s high”, which may contribute to the reported caffeine exercise benefits.
References
Magkos, F., Kavouras, S.A. Caffeine and ephedrine: physiological, metabolic and performance enhancing effects. Sports Med.2004;34(13):871 – 889.
Smith, A.P. Caffeine at work. Hum Psychopharmacol. 2005; Aug 20(6):441 – 445.
Jackman, M., Wendlin, P., Friars, D., Graham, T.E.:Metabolic, catecholamine, and endurance responses to caffeine during intense exercise. J Appl Physiol. 1996;81:1658 – 1663
Bruce, C.R., Anderson, M.E., Fraser, S.F., Stepto, N.K., Klein, R., Hopkins, W.G., Hawley, J.A. Enhancement of 2000-m rowing performance after caffeine ingestion. Med Sci Sports Exerc. 2000 Nov;32(11):1958 – 63.
Doherty, M. The effects of caffeine on the maximal accumulated oxygen deficit and short-term running performance. Int J Sport Nutr. 1998;8:95 – 104
Bell, D.G., Jacobs, I., Ellerington, K.: Effect of caffeine and ephedrine ingestion on anaerobic exercise performance. Med Sci Sports Exerc 2001;33:1399 – 1403
Anderson, M.E., Bruce, C.R., Fraser, S.F., Stepto, N.K., Klein, R., Hopkins, W.G., Hawley, J.A. Improved 2000-meter rowing performance in competitive oarswomen after caffeine ingestion. Int J Sport Nutr Exerc Metab 2000; Dec;10(4):464-75.
Cox, G.R., Desbrow, B., Montgomery, P.G., Anderson, M.E., Bruce, C.R., Macrides, T.A., Martin, D.T., Moquin, A., Roberts, A., Hawley, J.A., Burke, L.M. Effect of different protocols of caffeine intake on metabolism and endurance performance. J. Appl Physiol 2002; 93:990-999
Laurent, D., Schneider, K.E., Prusaczyk, W.K., Franklin, C., Vogel, S.M., Krssak, M., Petersen, K.F., Goforth, H.W., Shulman, G.I. Effects of caffeine on muscle glycogen utilization and the neuroendocrine axis during exercise. J Clin Endocrinol Metab. 2000;Jun;85(6):2170-5.
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