Eight glasses of water a day — is it backed by science?
Eight glasses of water a day — everyone says you need it. But is there actually a study behind it?
- Claim
- 8 GLASSES WATER A DAY
- Catch
- NO SINGLE NUMBER
- Verdict
- DRINK WHEN THIRSTY
The rule traces to a 1945 nutrition board note: about two and a half liters of water daily, most of it already in food and other drinks.
There's no study proving eight glasses of plain water prevents anything. Your needs depend on size, activity and climate — and coffee, tea and food all count.
Health bodies give total-water targets from all sources — about two point seven liters for women, three point seven for men — not eight glasses. Drink when you're thirsty.
The catch: total-water targets come from surveys, not trials proving eight glasses prevents disease. Needs vary — there's no single number for everyone.
SOURCES
- Valtin H. Drink at least eight glasses of water a day? Isn't that an exaggeration? Am J Physiol Regul Integr Comp Physiol. 2002;283:R993-R1004.
- National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for water. 2004.
For information only, not medical advice. Talk to a doctor if you have kidney or heart conditions.
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