written by: Pratik Patel
Coffee is one of the most popular beverages consumed all around the world, and yet most coffee consumers don’t know what caffeine does to their body besides to help them wake up in the morning and avoid a full blown caffeine withdrawal headache. Caffeine is a substance that acts on the central nervous system, mainly as a stimulant, that can aid in physical performance and help with alertness and cognition. With caffeine being one of the most thoroughly reviewed ergogenic aids, there is a lot of evidence that supports the consumption of caffeine to support improvements in both physical and mental performance. But, because caffeine has a diuretic effect on the body and has the potential to increase urine production, there is the belief that this could affect fluid balance, increase the risk for hyperthermia, and cause dehydration. Because of these potential negative effects, it is commonly believed that individuals should refrain from caffeine intake before or during exercise.
The research shows three main categories in which caffeine ingestion can correlate to dehydration; hydration status, electrolyte levels, and body temperature regulation.
Should you cut down or skip your coffee, tea or favorite caffeinated beverage when exercising?
Caffeine's effect on hydration status
When it comes to hydration status, it’s been shown that caffeinated beverages and water affect body water balance in a similar fashion both during exercise and in general. There are some studies that show that caffeine does cause an increase in urine production, but many others show that there is no relationship between the amount of fluid consumed and the appearance of increased urine production because of caffeine. Caffeine doses less than 226mg (equivalent to the amount found in 2-3 cups of coffee or 5-8 cups of tea) and even up to 553mg show no difference in the diuretic effect of caffeine vs water. When it comes to hydration status there is no evidence that caffeine causes fluid loss any greater than that of water (1).
Does it impact Electrolyte levels?
The consumption of caffeine does inhibit the reabsorption of sodium and may increase sodium excretion but when looked at as a whole, daily sodium balance remains positive. An adequate diet can provide enough sodium to cover urinary losses even when caffeinated beverages are consumed. There is no evidence that caffeine consumption causes an imbalance in electrolyte levels that is detrimental to exercise performance or health as long as caffeine is consumed in moderation (2).
How does caffeine impact body temperature regulation?
Many individuals caution the use of caffeine in hotter conditions, especially exercising in these conditions, due to the increase in heart rate caused by caffeine consumption and potential issues with temperature regulation. However, the research has found it has the opposite effect. Caffeine intake when compared to a control has little or no influence on human thermoregulation and circulatory strain (1). It has also been shown that caffeine intake up to 6mg per kg of bodyweight per day when compared to zero intake did not alter fluid-electrolyte, exercise endurance or thermoregulatory responses during exercise heat training (3). Because caffeine does not affect fluid balance nor causes dehydration, the body’s ability to thermoregulate is not affected. Overheating is not a concern in hot environments for those consuming caffeine vs water (1).
Should you refrain from drinking coffee because of the fear of dehydration?
We’re not here to take away your morning cup of coffee, nor are we trying to add an iced coffee into your daily training regimens. We’re simply here to present some of the robust research about how caffeine affects physical performance. Even though caffeine results in a slight increase in urine production, it has no effect on fluid or electrolyte balance, nor does it affect temperature regulation in the body with intakes of up to 6mg* per kg of bodyweight per day. Caffeinated beverages do not directly cause dehydration and it can even contribute to daily fluid intake and balance in a similar manner that water does.
*NOTE: 6mg per kg of bodyweight is equivalent to 490mg of caffeine for the entire day or the equivalent of about 5 cups of brewed coffee for a 180lb individual. It should be noted that there is no need for an individual to consume 6mg per kg bodyweight per day; this is the upper limit that has been studied and shown not to effect hydration status.
(1) Armstrong, L. E., Casa, D. J., Maresh, C. M., & Ganio, M. S. (2007). Caffeine, fluid-electrolyte balance, temperature regulation, and exercise-heat tolerance. Exercise and sport sciences reviews, 35(3), 135–140.
(3) Roti, M. W., Casa, D. J., Pumerantz, A. C., Watson, G., Judelson, D. A., Dias, J. C., Ruffin, K., & Armstrong, L. E. (2006). Thermoregulatory responses to exercise in the heat: chronic caffeine intake has no effect. Aviation, space, and environmental medicine, 77(2), 124–129.