Coffee consumption and fluid balance

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Coffee and Health houses current scientific information on a wide range of coffee-related topics. This blog post focuses on the topic of coffee consumption and fluid balance. Below is an overview of this topic which includes information on the effect of coffee on endurance exercise and exercise performance.

The study of the effect of coffee on fluid balance is split into two areas. These are caffeine intake during exercise and caffeine intake at rest in the general population.

According to the latest research, in normal life activities, caffeine consumption does not lead to dehydration. Studies also conclude that during exercise, moderate caffeine consumption is beneficial for endurance performance and does not contribute to dehydration.

The research supports that advice to abstain from drinking moderate amounts of caffeinated coffee in order to maintain adequate fluid balance is unfounded. While there may be a mild, short-term diuretic effect of caffeine, this effect is not strong enough to outweigh the benefits of fluid intake from coffee consumption. Coffee drinking in moderation also contributes to our fluid intake and does not lead to dehydration, with black coffee containing more than 95% water.

Coffee, caffeine and hydration in the general population

No increase in urinary excretion in regular caffeine consumers
A 1997 study reported a significant increase in the volume of urine excreted in individuals drinking coffee, compared with those drinking an equivalent amount of water. The subjects in the study had abstained from ingesting any caffeine for five days prior to the treatment, effectively making them ‘caffeine naïve’. This more pronounced effect on urinary excretion following re-introduction of caffeine is well-documented within the literature.

Short-term stimulation of urine output has also been found to occur in individuals who have been deprived of caffeine, and then given fairly large doses in one sitting. However, it appears that a tolerance to caffeine develops, and these effects are diminished in individuals regularly consuming moderate amounts of coffee.

Caffeinated beverages contribute to daily fluid intake
A Beverage Guidance Panel in the U.S. has stated that caffeine consumption, of up to the equivalent amount found in approximately five cups of regular coffee a day, does not cause dehydration.

Similarly, proceedings from a conference in North America have advised consumers that drinking a variety of caffeinated beverages can contribute to meeting the body’s fluid requirements.

Caffeine, hydration and exercise performance
There is no evidence of any detrimental effects of caffeine on exercise performance. This is supported by a comprehensive review in 2002 of the literature on caffeine and fluid balance during exercise. The review concluded that a daily intake of 300mg of caffeine, which is the amount found in approximately three regular size cups of coffee, may have a mild, short-term diuretic effect similar to that of water, with no significant effect on overall fluid balance.

A more recent survey (2010) also found no contribution of moderate levels of caffeine (constituted by less than 300mg) on dehydration, either at rest or during exercise. The survey also suggested that similar conclusions can be drawn for caffeine’s long-term effects.

Caffeine beneficial in endurance exercise
Available evidence shows that caffeine ingestion in moderate quantities is beneficial for sports performance in endurance athletes. Additionally, a 2010 review does not support claims that caffeine induces diuresis during exercise.

Caffeine does not adversely affect temperature regulation
There are several factors which can reduce heat tolerance during exercise in hot environments. Reviews of the effects of caffeine show no evidence that caffeine induces chronic dehydration, or negatively affects temperature regulation, in hot environments.

In conclusion, scientific evidence supports that moderate consumption of caffeinated beverages, including coffee, does not lead to dehydration. Advice to abstain from drinking moderate quantities of caffeinated coffee, because of potential negative effects on fluid balance, is therefore unfounded. Caffeinated beverages, including coffee, can in fact contribute to daily fluid intake according to current advice.

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