Caffeine and fluid balance during exercise

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A review of 10 studies, which scrutinised the different protocols and the results obtained, concluded:

–     A daily intake of 300mg of caffeine induces only a mild, short-term diuretic effect, similar to that of water, with no significant effect on overall fluid balance.

–    There is no evidence that caffeine is detrimental during exercise in hot climates when fluid losses are maximal.

–    The long-term effects of caffeine on fluid balance are not adequately reported. There are a number of methodological limitations. For example, urine should be collected over longer periods, at least 24 hours.

–    Statements suggesting the avoidance of caffeinated beverages before, and during, exercise are unfounded.

A more recent survey reviews the various components of hydration during sport. As far as caffeine is concerned, ingestion of moderate to low levels (less than 300mg) in one shot did not contribute to dehydration either at rest or during exercise. Similar conclusions can be drawn for the long-term ingestion of caffeine.

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