October 3, 2025
Coffee and Hydration
The belief that coffee dehydrates you is one of the most persistent myths in nutrition. It is wrong. Coffee is a mild diuretic, meaning it modestly increases urine production. But the water content in a cup of coffee more than offsets the diuretic effect. You retain more fluid than you lose. Coffee hydrates you, on net.
The Research
A 2014 study in PLOS ONE compared hydration in men drinking 4 cups of coffee per day versus 4 cups of water per day over 3 days. Result: no significant difference in hydration markers. A 2003 review concluded that caffeine doses below 500mg per day do not produce a diuretic effect significant enough to cause dehydration. Habitual coffee drinkers develop tolerance to the diuretic effect.
The Simple Rule
Drink coffee. Also drink water. Do not worry that one is undoing the other. Your morning coffee counts toward your daily fluid intake. During exercise, coffee is not a substitute for water. See the performance benefits of pre-workout coffee but hydrate with water during activity. Find a shop near you and enjoy your cup without guilt.
Keep reading: How Much Coffee Is Too Much, Coffee Before a Workout, How Much Caffeine Is in Coffee.
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