Hydration myths vs facts

The Myth

• Coffee is often said to be dehydrating because caffeine has a mild diuretic effect.
• This belief led to the idea that coffee ‘doesn’t count’ toward daily fluid intake.

The Facts

• Mild Diuretic Effect: Caffeine can increase urine output slightly, especially in non-habitual users.
• Tolerance: Regular coffee drinkers develop tolerance, so the diuretic effect largely disappears.
• Net Fluid Balance: A cup of coffee is still ~95% water. The hydration from water outweighs any minor diuretic effect.
• Scientific Consensus: Research shows coffee contributes positively to daily fluid intake and does not cause dehydration.

Supporting Evidence

• Studies comparing coffee vs water found no significant difference in hydration status among habitual coffee drinkers.
• The Institute of Medicine (U.S.) recognizes coffee and tea as valid sources of hydration.

Practical Considerations

• Moderate intake (3–4 cups/day) is safe and hydrating for most adults.
• Excessive caffeine (>500 mg/day) may increase bathroom visits, but still does not lead to clinical dehydration.
• Individual sensitivity varies—people prone to urinary frequency may experience stronger effects.

Summary

Coffee is not dehydrating. Despite its mild diuretic action, the water content provides hydration. For habitual drinkers, coffee counts toward daily fluid needs just like other beverages.

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