Does coffee dehydrate you?

Caffeinated coffee at moderate intake (1–3 cups per day) does not produce net dehydration in habituated coffee drinkers, the mild diuretic effect of caffeine is completely offset by the fluid volume in the beverage itself, and chronic coffee consumers show no difference in hydration markers compared to non-coffee drinkers in hydration status studies (Killer et al., PLOS ONE, 2014).

The coffee-dehydration myth has been persistently taught by athletic trainers, nutritionists, and physicians who misapplied the diuretic pharmacology of caffeine to caffeinated beverages. Caffeine in isolation is mildly diuretic. Coffee is a caffeinated aqueous solution, the 250 ml of water in a cup of coffee overwhelms the mild diuretic effect. At very high caffeine doses (>300–500 mg in a short window, equivalent to 3–5 large coffees quickly), a net diuretic effect can occur, particularly in non-habituated individuals. For daily moderate coffee drinkers, coffee counts toward daily fluid intake.

Honesty Scale: Solid (1) for moderate coffee consumption not producing net dehydration in habituated consumers.

What to do: Count your daily coffee and tea toward your total fluid intake. No additional compensation for coffee is needed unless you are drinking 5+ large coffees per day in a non-habituated state.

For the full picture, read The Hydration Deep Dive