Citat:
We conclude, based on the information above, that the popular beliefs about caffeine in regard to fluid balance, electrolyte balance, and exercise-heat tolerance are incorrect.
Because dehydration is absent, the body's ability to regulate temperature (i.e., via sweating and increased skin blood flow) is not impaired, even in a hot environment. In turn, because hyperthermia is not greater when caffeine is consumed (vs a water placebo), exercise performance is enhanced without increased physiological strain.
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Exerc Sport Sci Rev. 2007;35(3):135-140.
Citat:
The idea that caffeine is a diuretic originated around 1930 with experiments on just a few humans and with animal research. The results indicated that caffeine causes an increase in urine production, which is true. But then, water does the same thing. Does that mean that we shouldn’t drink water? ...the diuretic activity of caffeine is similar to that of water.
For decades, health and exercise experts have cautioned that caffeine causes dehydration, despite a lack of scientific evidence to support that idea. It’s fair to ask why hospitals aren’t filled with dehydrated people.
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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, Judelson DA, Watson G, Dias JC, Sökmen B, Casa DJ, Maresh CM. Fluid, electrolyte, and renal indices of hydration during 11 days of controlled caffeine consumption. International Journal of Sport Nutrition & Exercise Metabolism 15:252-265, 2005.