The Kona-day race morning Perk: A Return To Empowering Coffee Spurred on advice from people like Peter Reid and Mark Allen, some triathletes Linsey Corbin as Montana, a fast break of one month from coffee, hours before the gun goes off Hawaii Ironman
Dehydration and Coffee

The coffee itself is the diuretic, or is it the caffeine in coffee?

If I drink decaf coffee, it is still a diuretic?

Caffeine, not necessarily a diuretic a belief long held the coffee may be on the way to be rebutted. Sports nutritionists and physiologists often counsel active people to avoid caffeine because it could act as as a diuretic and therefore negative effects on performance and health. A study published in June 2005 in the International Journal of Sport Nutrition and Exercise metabolism examined the effects of daily consumption of caffeine in 59 healthy men. For the first 6 days of the study, all participants consumed 3 milligrams of caffeine per kilogram of body weight. On days 7 to 11, they were randomly assigned to receive no caffeine, or 3 or 6 mg of caffeine per kilogram of body weight. Whatever the dose of caffeine, the participants "all measures of hydration and electrolyte balance were within normal limits. These findings challenge the longstanding belief that, when consumed regularly, caffeine acts as a diuretic.

Caffeine