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  July 22, 2002

Armstrong's Study Shows Caffeine Does Not Increase Dehydration
By Janice Palmer

Caffeine is not the diuretic demon people are often told to avoid during exercise or while working in extreme environmental conditions.

In fact, caffeine is no more a diuretic than water, according to a research review article by Larry Armstrong, a professor of exercise and environmental physiology at the Neag School of Education.

Image: Coffee Cup

For decades, health and exercise experts have warned that consuming caffeine and caffeinated beverages can lead to dehydration. But Armstrong, an avid runner and a well respected scientist in the fields of thermo-regulation and human performance, observed evidence to the contrary, so he investigated whether abstaining from caffeinated beverages was scientifically and physiologically justifiable.

"While there have been several studies done that show caffeine is a mild diuretic, there is no evidence that exercise, when combined with the consumption of caffeine or caffeinated beverages, will result in chronic dehydration, and this is contrary to the advice of most exercise physiologists, physicians and dieticians," explains Armstrong, who has been conducting fluid balance research since 1980.

"Therefore, the health and performance of athletes and recreational enthusiasts will not be impaired if they consume caffeine and caffeinated beverages in moderation and eat a well-balanced diet," he says. The National Coffee Association funded his study.

Among his findings:

  • When caffeine or a caffeinated beverage is consumed, the body retains some of the fluid;

  • Caffeine consumption causes a mild diuresis very similar to that of water (water, when consumed in large volume, increases urine output);

  • There is no evidence that consumption of caffeinated beverages causes a fluid-electrolyte imbalance that is detrimental to health or exercise performance;

  • A person who regularly consumes caffeine has a higher tolerance to the diuretic effect;

  • The determination of safety or risk of consuming caffeine and caffeinated beverages depends on several factors, including the amount consumed and tolerance to caffeine.

For decades, caffeine has been a favorite stimulant for athletes trying to make weight or enhance muscle definition before competition. Both the National Collegiate Athletic Association (NCAA) and the International Olympic Committee classify caffeine as a banned substance, because of its ergogenic properties. But while there are instances of abnormal and unhealthy diuretic use by athletes, Armstrong reports that "these examples should not be interpreted to mean that the average person who participates in exercise several times a week would be jeopardizing his or her health by consuming one or two caffeinated products each day."

Because the scientific literature analyzed by Armstrong focused on moderate amounts of caffeine (one to four cups of coffee a day), he advises that further research be conducted to determine if chronic, high-dose caffeine consumed over several days results in fluid-electrolyte imbalances.

His findings were published in the June issue of the International Journal of Sport Nutrition and Exercise Metabolism and were recently presented at the American College of Sports Medicine conference in St. Louis, Missouri.

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