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 10-14 and that it can improve endurance performance14. 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.
While the relation between hydration status and physical activity has been an area of extensive research, the importance of hydration for maintenance of good health and cognitive performance is increasingly recognised1.
It is a common belief that drinking caffeinated coffee can lead to dehydration. The mild, short-term diuretic effect of caffeine has been described an “unproven myth”2. Scientific evidence looking at the effects of caffeine on fluid balance does not support this commonly held belief.
The content in this overview was last edited in May 2017. Papers in the research section and further resources are added regularly.