Caffeine is a mild diuretic, increasing water loss through urination. Because caffeine is a mild diuretic, polyuria is a possibility.
In its 2005 consensus on hydration, the American College of Sports Medicine wrote, ‘Caffeine ingestion has a modest diuretic effect in some individuals but does not affect water replacement in habitual caffeine users, so caffeinated beverages such as coffee, tea, soft drinks) can be ingested during the day by athletes who are not caffeine naïve’.
A definitive study by researcher R.D Wemple in 1997 demonstrated that although caffeine ingestion during rest causes a very mild diuresis, or increase in urinary output, over a 4 hour period.
However, a tolerance to the mild diuretic effect of caffeine at rest rapidly occurs and the diuretic effect is not present in subjects who regularly consume some caffeine. Only single large doses of 250 to 300 milligrams seem to cause any significant diuretic action.
Caffeine is a mild diuretic
