Caffeine: Is it dehydrating or not?….the answer may suprise you!

  • Katherine Zeratsky, R.D., L.D.
  • photo of Katherine Zeratsky, R.D., L.D. Katherine Zeratsky, R.D., L.D.

    As a specialty editor for the nutrition and healthy eating guide, Katherine Zeratsky helps you sort through the facts and figures, the fads and the hype to learn more about nutrition and diet.

    A Marinette, Wis., native, Katherine is certified in dietetics by the state of Minnesota and the American Dietetic Association. She has been with Mayo Clinic since 1999.

    She is active in nutrition-related curriculum and course development in wellness nutrition at Mayo Clinic in Rochester, Minn., and nutrition education related to weight management and practical applications of nutrition-related lifestyle changes.

    Other areas of interest include food and nutrition for all life stages, active lifestyles and the culinary arts.

    She graduated from the University of Wisconsin-Madison, served a dietetic internship at the University of Iowa Hospitals and Clinics, and worked as a registered dietitian and health risk counselor at ThedaCare of Appleton, Wis., before joining the Mayo Clinic staff.

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?


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 has a diuretic effect only if you consume large amounts of it — more than 500 to 600 milligrams (the equivalent of 5 to 7 cups of coffee) a day.

Still, caffeinated drinks at these levels 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.

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  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. Lopez RM, et al. The influence of nutritional ergogenic aids on exercise heat tolerance and hydration status. Current Sports Medicine Reports. 2009;8:192.
  4. Ruxton CH, et al. Black tea is not significantly different from water in the maintenance of normal hydration in human subjects: Results from a randomized controlled trial. British Journal of Nutrition. In press. Accessed June 2, 2011.
  5. Zeratsky KA (expert opinion). Mayo Clinic, Rochester, Minn. June 2, 2011.

AN01661 Aug. 20, 2011

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