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  • With Mayo Clinic nutritionist

    Katherine Zeratsky, R.D., L.D.

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Mayo Clinic Health Manager

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Question

Caffeine: Is it dehydrating or not?

I've been seeing ads that say cola and coffee drinks hydrate you as well as water does. Is this true?

Answer

from Katherine Zeratsky, R.D., L.D.

It is true. Researchers used to believe that caffeinated drinks had a diuretic effect. This means that you would urinate more after drinking them, which could increase your risk of becoming dehydrated. Recent research shows that this is not true and that caffeine only has a diuretic effect if you consume large amounts of it — more than 500 to 600 milligrams (or 4 to 7 cups of coffee) a day.

Still, caffeinated drinks can make you jittery, sleepless or anxious. Water is probably your best bet to stay hydrated. It's calorie-free, caffeine-free, inexpensive and readily available.

Next question
Coffee and health: What does the research say?
References
  1. Armstrong LE, et al. Caffeine, fluid-electrolyte balance, temperature regulation, and exercise-heat tolerance. Exercise and Sport Sciences Review. 2007;35:135.
  2. Maughan RJ, et al. Caffeine ingestion and fluid balance: A review. Journal of Human Nutrition and Dietetics. 2003;16:411.
  3. Grandjean AC, et al. The effect of caffeinated, non-caffeinated, caloric and non-caloric beverages on hydration. Journal of the American College of Nutrition, 2000;19:591.

AN01661

Aug. 21, 2009

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