Fluid balance is a particularly important topic amongst athletes, as dehydration is always a concern since it is associated with reduced performance. Caffeine may exert a short-term diuretic effect but research suggests that this does not counter-balance the effects of the fluid intake from coffee drinking28-35. Drinking caffeinated coffee in moderation can help to maintain adequate fluid balance28-35.
A comprehensive review concluded that a daily intake of 300mg of caffeine (the amount found in approximately 3 regular cups of coffee) induces only a mild, short-term diuretic effect, similar to that of water, with no significant effect on overall fluid balance28. The authors stated that there is no evidence that caffeine is detrimental during exercise in hot climates when fluid losses are maximal28. The study further confirmed that statements suggesting the avoidance of caffeinated beverages before and during exercise are unfounded28.
A 2014 meta-analysis considering the role of caffeine in fluid balance in adults during rest and exercise concluded that although caffeine produced a minor diuretic effect this was negated by exercise. The authors also suggested that concerns regarding unwanted fluid loss associated with caffeine consumption are unwarranted particularly when ingestion precedes exercise33.
A further study published in 2014 found no significant differences in measures of hydration status between those who drank coffee or those who drank water, concluding that coffee consumed in moderation by regular male coffee drinkers had similar hydrating qualities to water34.
In 2004 the International Olympic Committee (IOC) officially removed caffeine from its list of banned substances stating that historical suggestions that caffeine’s mild, short-term diuretic effect may impair physical performance are unfounded.
Further information on fluid balance can be found here.