The study of the effect of coffee, and caffeine in particular, on fluid balance can be split into two distinct areas: caffeine intake in the general population and caffeine intake specifically during exercise.
Black coffee contains more than 95% water15. Research suggests that coffee drinking in moderation contributes to fluid intake and does not lead to dehydration, or significant loss of body fluid3-8. Moderate coffee consumption is typically defined as 3-5 cups per day, based on the European Food Safety Authority’s (EFSA) review of caffeine safety14.
Fluid in the body is important: EFSA has concluded that a cause and effect relationship has been established between the dietary intake of water and the maintenance of normal and physical cognitive function16. Whilst there is some indication of a short-term diuretic effect of caffeine intake, this effect does not counter-balance the effects of the fluid intake from coffee drinking5. Drinking caffeinated coffee in moderation can therefore help maintain adequate fluid balance3-8.
Research also suggests that a moderate intake of caffeine does not contribute to dehydration during exercise10-14 and that it can improve endurance performance (EFSA). The European Food Safety Authority (EFSA) in its Scientific Opinion on Caffeine noted that caffeine intake does not affect body temperature or hydration status beyond what could be expected from the exercise conditions14.
The content in this Overview was last edited in May 2017. Papers in the Latest Research section and further resources are added regularly.
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