In a recent review article, “Caffeine, Body Fluid-Electrolyte Balance, and Exercise Performance,” published in the June 2002 issue of the International Journal of Sport Nutrition and Exercise Metabolism, researcher Lawrence E. Armstrong, a professor of exercise and environmental physiology at the University of Connecticut, found that caffeine is not the dehydrating demon some people believe. In fact, he concluded that caffeine is no more a diuretic than water.

For years, health and exercise experts have cautioned that consuming caffeine and caffeinated beverages can lead to dehydration. But Armstrong, an avid runner and a well-respected scientist in the field of thermoregulation and human performance, observed evidence to the contrary, so he reviewed the scientific literature to determine 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 dietitians,” explains Armstrong, who has conducted fluid balance research since 1980.

Supporting Armstrong’s findings is an American Journal of Physiology August 2002 review of the literature on hydration by Dr. Heinz Valtin that cites a University of Nebraska study, which found that caffeinated beverages may be counted toward the daily fluid total.

Armstrong’s analysis of the scientific literature that was focused on moderate amounts of caffeine (equivalent to one to four cups of coffee a day) indicates:

• When consuming a caffeinated beverage, the body retains some of the fluid.
• Moderate caffeine consumption causes a mild diuresis very similar to that of water (water, when consumed in large volume, increases urine output).
• A person who regularly consumes caffeine has a higher tolerance to the diuretic effect.
• There is no evidence that consumption of caffeinated beverages causes a fluid-electrolyte imbalance that is detrimental to health or exercise performance.

Although additional research could help confirm these findings, Armstrong’s analysis of the literature is encouraging for regular consumers of caffeinated beverages. The article can be accessed at http://www.humankinetics.com/products/journals/.