The popular ergogenic aid might not be the powerful diuretic it was once thought to be. 

In North America, about 90 percent of adults regularly consume caffeine, mainly in liquid form, whether from cola, tea, coffee, or other caffeine-laced beverages. Caffeine is also present in cocoa and chocolate. Given this statistic, it is safe to assume that most endurance athletes ingest caffeine on a daily basis and perhaps even during training and competition. While the proper use of caffeine can enhance physical performance, it has long been labeled as a diuretic, or a substance that actually increases fluid losses by increasing urine production. Athletes have often been cautioned to limit their daily caffeine and not to count caffeine-containing beverages toward total daily fluid intake.

MORE: Do The Performance Benefits of Caffeine Come At A Cost?

Is caffeine truly dehydrating? For almost a decade scientists have challenged this assumption about caffeine. Reassessments of existing data and new studies of the effects of  caffeine on the hydration status of athletes show that, while caffeine often does act as a mild diuretic, stimulating urine production from the kidneys, it does not produce a greater increase in urine volume when compared with the same volume of water or caffeine-free fluid consumption. One study compared the effects of caffeinated and noncaffeinated beverages (both caloric and calorie-free) on the daily hydration status of healthy males. Over a twenty-four-hour period, there were no significant hydration differences among the various beverages. Another study had athletes rehydrate with a caffeinated beverage between exercise periods. The researchers found little evidence to support that caffeine can slow down an athlete’s efforts to rehydrate. Bottom line: Caffeine is not the powerful diuretic it was once thought to be.

RELATED — Daily Hydration Needs: Water, The First Nutrient

Endurance athletes can rest assured that a moderate daily intake of caffeine of about 1.4 to 2.7 milligrams per pound (3–6 mg/ kg) of body weight should not compromise their daily hydration status when consumed within the context of a well-balanced diet. Caffeine intakes safely falling into this range would be 230 to 460 milligrams of caffeine for a 170-pound (77 kg) man, or 190 to 380 milligrams for a 140-pound (64 kg) woman. A can of soda contains about 40 to 45 milligrams of caffeine, but the amount of caffeine in a cup of coffee varies widely depending on how the coffee is brewed (for the caffeine content of some beverages, see Table 1.1). Certainly, caffeine-containing drinks should not compromise the majority of your fluid intake.

Avoid excessive doses of caffeine, however, as high amounts are associated with side effects such as nervousness, gastrointestinal upset, irritability, and insomnia. Higher doses can also negatively affect your hydration status and do not result in performance improvements much beyond the moderate doses. Heavy coffee drinkers may find that the acidic nature of the drink can cause reflux.

This article is adapted from the new edition of Sports Nutrition for Endurance Athletes by Monique Ryan, MS, RD, CSSD, LDN with permission of VeloPress. 


About The Author:

Monique, Ryan, MS, RD, CSSD, LDN, is a seasoned and trusted sports nutritionist with nearly 30 years of professional experience helping elite and age-group endurance athletes and major league sports teams to optimize their nutrition. She is also the founder of Personal Nutrition Designs, based in the Chicago area. 


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