Coffee Makes You Dehydrated: Say What?

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It has long been thought that coffee and other caffeine-containing beverages are dehydrating and don’t count toward your daily fluid intake. In fact, some go as far as recommending one cup of water for every cup of Joe you consume. Most of us know that caffeine is a diuretic (it makes us have to go pee), but does it deplete our bodily fluids?


The Straight Talk
In his review, “Caffeine, Body Fluid-Electrolyte Balance, and Exercise Performance,” Lawrence E. Armstrong, a professor of exercise physiology at the University of Connecticut disproves the notion that caffeinated beverages rob us of our precious fluids. By reviewing the scientific research on the subject, he concludes that although caffeine, like water, is a mild diuresis (it increases excretion of urine), moderate caffeine consumption does not produce a “fluid-electrolyte imbalance” that can affect health or exercise performance. Furthermore, we retain roughly the same amount of fluid after drinking a caffeinated beverage as we do after drinking water.


Even more encouraging for habitual coffee consumers is the finding that those with caffeine tolerance have reduced likelihood that a fluid electrolyte imbalance will occur. The more regular your caffeine habit, the more fluid your body is conditioned to retain.


Other findings support his conclusions. A small study done at the University of Nebraska tested the body weight, urine output, and blood of eighteen subjects after they consumed caffeinated and non-caffeinated beverages. They determined that there was “no significant differences in the effect of various combinations of beverages on hydration status of healthy adult males.” The Institute of Medicine expert panel on water and electrolyte intake asserts that the diuretic effects of caffeine are transient, and that coffee, tea, and colas can contribute to total water intake.


The Takeaway
Moderate caffeine consumption won’t dehydrate you and can actually help you reach your overall daily fluid intake. Make mine a double.


Say What? is a series created to support or debunk common health myths. If you have a question for Brie, please send it to her in care of the editor at rbrown@realgirlsmedia.com.


Updated November 14, 2008

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