It is a common misconception that caffeine can lead to dehydration during exercise. Research examining the effect of caffeine on hydration levels during exercise shows that caffeine does not have a significant effect on hydration and does not lead to increased dehydration.
Sweat
To make a long, complicated story short, sweat is filtered plasma. As an individual continues to sweat, plasma levels decrease. As plasma levels drop, they affect the body's ability to cool and can ultimately lead to heat-related issues. If caffeine did act as a diuretic during exercise, it would worsen the situation.
Caffeine as an Ergogenic Aid
Caffeine acts as an ergogenic aid primarily as a CNS stimulant lowering the feeling of exertion during endurance events. Caffeine also causes an increased release of free fatty acids, which assist in oxidative energy supply during endurance events. High levels of caffeine are not needed to realize increased performance. The equivalent of 2 to 2.5 cups of coffee is sufficient, with no increased performance benefits beyond that amount.
Caffeine As Diuretic During Exercise
Caffeine is considered a diuretic due to the fact that it increases urination in those that are not accustomed to ingesting caffeine. During exercise, antidiuretic hormone, or Vasopressin, is released in order to conserve hydration levels by decreasing urination. Aldosterone release is also stimulated during exercise in order to retain both sodium and water. The release of both of these hormones would offset any possible diuretic effects of caffeine.
Side Effects of Caffeine
While caffeine does not lead to increased dehydration during exercise, there are possible side effects when consuming caffeine as an ergogenic aid. Individuals unaccustomed to ingesting coffee may experience gastrointestinal distress. Other possible side effects include: headache, irritability, muscle twitching, arrhythmia, increased heart rate and insomnia. Before utilizing caffeine as an ergogenic aid, know how your body responds.
References
- "The Complete Book of Road Cycling and Racing"; Will Peveler Ph.D.; 2009
- "Exercise Physiology: Nutrition, Energy, and human Performance"; William McArdle, et al.; 2010
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