FOR IMMEDIATE RELEASE
CAFFEINATED BEVERAGES MAY HELP IN
ATHLETIC PERFORMANCE
New York, N.Y. – October 21, 2004 – A review of scientific studies comprising 30 years of research gave encouraging news to coffee lovers who value their exercise: caffeinated beverages do not adversely affect exercise performance. They may actually improve endurance and reduce fatigue in certain types of intense exercise, such as cycling and running for more than four to eight minutes. Furthermore, the scientific consensus is that caffeine does not cause a fluid-electrolyte imbalance.
The
literature review had a two-fold purpose: 1) to evaluate the
controlled studies that explored the effects of caffeine on
dehydration and exercise performance, and 2) to determine whether
there is any scientific or physiological rationale for abstaining
from caffeinated beverages prior to exercise. The studies focused on
both athletes and recreational enthusiasts.
Lawrence Armstrong, Ph.D., Professor of Environmental Physiology in the Human Performance Laboratory at the University of Connecticut, Storrs, spoke today at the New York Academy of Sciences at a symposium for science writers. Coffee and Your Health: Surprising Findings.
Dr. Armstrong told the group that researchers had found that 82-92% of adults in North America regularly consume caffeine in some form. Adult coffee drinkers in the United States consume 200-400 mg of caffeine each day, which translates into two to four cups of coffee each day. Furthermore, 20-30% of these adults drink of up six cups of coffee each day.
The per capita consumption of dietary caffeine worldwide is 70 mg per day, which is almost entirely from beverages: 54% from coffee, 43% from tea, with 3% coming from other sources. Of course, the amount of caffeine in a cup of coffee or tea varies with the strength of the beverage and the size of the cup. Some prescription medications and over-the-counter analgesics also contain caffeine, and there is a negligible amount of caffeine in chocolate and other confectionery items.
According to Dr. Armstrong, other studies have shown, “Although soft drinks provide a fraction of the amount of caffeine found in coffee and tea, 98% of American youngsters from five to 18 years old consume some caffeine each day. This is due largely to the popularity of soft drinks among children.”
The physiologist explained that there has been a suspicion for years that caffeine might improve endurance performance, and since it is a central nervous system stimulant, athletes have used it in an attempt to improve their performance. According to Dr. Armstrong’s summary of research, studies have shown that caffeine does indeed have an ergogenic effect, and it can improve endurance time in prolonged events. He told the group, “Divergent research findings suggest that different caffeine-induced effects may be at work in different types of exercise.”
There are many factors that come into play, he added, including how much caffeine the athlete has consumed both in the past and just before the event, the type of exercise involved, what he or she ate prior to the activity, the extent to which the athlete has trained, and of course, individual variation.
The diuretic effect of coffee was also evaluated in previous studies which Dr. Armstrong reviewed. The mild diuretic effect in coffee, tea and soda stems from their active agents, classified as methylxanthines. Dr. Armstrong explained, “The caffeine in coffee, tea, and soft drinks is 1,3,7-trimethylxanthine. Tea contains theophylline – 1,3-dimethylxanthine. Theobromine is found in tea, chocolate and cocoa as 3,7-dimethylxanthine. All three compounds are central nervous system and cardiac stimulants, as well as mild diuretics in some situations.
Both serious athletes and weekend athletes consume a number of beverages that, when taken in large volume, have a diuretic effect. It is interesting to note that researchers have shown that fluid-electrolyte replacement beverages have diuretic activity, and that even water is a diuretic. At less than 300 mg a day, the diuretic activity of caffeine is similar to that of water.
Dr. Armstrong noted that, “…virtually no evidence exists in the scientific literature that caffeine exaggerates dehydration and electrolyte loss to the point that it impairs exercise performance.” He told the science writers that neither athletes nor recreational enthusiasts will incur detrimental fluid-electrolyte imbalances if they drink caffeinated beverages in moderation and eat a well-balanced diet.
In addition to performing the review of other investigators’ work mentioned above, Dr. Armstrong discussed his own recently completed research, presented in the paper, Fluid-electrolyte and renal indices of hydration during eleven days of controlled caffeine consumption (in review).
He told the science writers, “Our recent investigation determined if three levels of controlled caffeine consumption affected fluid-electrolyte balance and renal function differently. Fifty-nine active males (mean + SD; age, 21.6 + 3.3 y) consumed 3 mg caffeine· kg-1·d-1 on days 1-6 (equilibration phase). On days 7-11 (treatment phase), subjects consumed either 0 mg (C0; placebo; n=20), 3 mg (C3; n=20), or 6 mg (C6; n=19) caffeine/kg body weight/day in capsules; no other dietary caffeine intake was allowed. The subjects maintained detailed records of food and fluid intake.”
Dr. Armstrong noted, “There were no significant differences between groups C0, C3 and C6 (P>0.05) for any of the hydration-relevant variables, including urine volume.”
He concluded, “We found no evidence of acute or chronic dehydration in C3 or C6 during 11 days of controlled caffeine consumption. Our findings question the widely accepted notion that caffeine acts chronically as a diuretic.“
Armstrong, LE. Caffeine, body fluid-electrolyte balance, and exercise performance. International Journal of Sport Nutrition and Exercise Metabolism. 2002. 12:189-206 2002.
Armstrong, LE, Pumerantz, AC, Roti, MW et al. Fluid-electrolyte and renal indices of hydration during eleven days of controlled caffeine consumption. July 2004. In review.
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