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Why Does Caffeine Make You Dehydrated?

author image Virginia Franco
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Why Does Caffeine Make You Dehydrated?
A woman is drinking from a coffee mug. Photo Credit: DAJ/amana images/Getty Images

The human body contains two-thirds water. If you do not drink enough liquid, or lose more fluids than what your body needs to function normally, you will become dehydrated. Conventional wisdom has said for years to keep caffeine at a minimum, in part to avoid dehydration. While not false, caffeine’s ability to dehydrate has been exaggerated.

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Modern Myth

Medical experts have warned for years that caffeine is a strong diuretic. The notion believed by many is that by drinking caffeinated drinks like coffee, tea and colas, you will need to urinate so frequently you could become dehydrated if you’re not careful.

Diuretic Effect

Caffeine appears to have a diuretic effect only when consumed in excess. An excessive amount is more than 500 to 600 mg a day, or the equivalent of between four and seven cups of coffee daily, according to


In moderation, caffeine is as strong a diuretic as water. Various investigations comparing caffeine with water or a placebo seldom noted an increase in urine volume, according to an "International Journal of Sport Nutrition and Exercise Metabolism" June 2002 review of 10 previous studies led by scientists at the University of Connecticut.

Common Dehydration Causes

Although caffeine does not appear to dehydrate, other things can. Vomiting and diarrhea, such as that occurring with a stomach bug, can deplete your water reserves, as can diet supplements like laxatives or diuretics that promise to help you shed “water weight.” It is important to be aware of dehydration signs and take precautions to avert dehydration and replenish fluids.

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