Myth: Can a Cup or Two of Coffee Cause Dehydration?

Does a cup or two of java in the morning cause dehydration? It’s a question researchers have been exploring for years, and results have been fairly conclusive. Caffeinated beverages, in moderation, aren’t likely to cause dehydration, the research agrees.

That’s right. Although caffeine itself can cause dehydration, the additional water in coffee and tea helps outset the mild diuretic effect of caffeine. In fact, your daily coffee habit can actually be added to your overall hydration budget.

According to one recent study, moderate levels of coffee can actually provide “similar hydrating qualities to water." Researchers at the University of Birmingham looked at what effect drinking coffee, instead of water, would have on overall hydration. In the study, 50 men, who regularly drank between three and six cups of coffee per day, completed two phases. In the first, coffee was their primary source of fluids. Then, they gave up coffee and drank an equal amount of water.

The results: Participants didn’t experience differences in hydration levels, which may have been a result of having developed a tolerance. Yet, the study was just the most recent example of research that has debunked the coffee-dehydration myth. In fact, the Institute of Medicine concluded in its 2004 Dietary Reference Indexes report that caffeinated beverages can contribute to daily water needs, as well, because the diuretic effect is minimal.

Excessive Caffeine Increases the Risk

So can you drink as much coffee as you want, without experiencing any hydration consequences? The short answer is no. In excess, the diuretic effect of caffeine is amplified, which increases the risk for dehydration. Plus, overindulging on java can cause adverse symptoms like the jitters, headaches and insomnia.

Is there a set limit? About 500 milligrams of caffeine per day is a great benchmark, according to one Mayo Clinic nutritionist. That’s about three to six cups of coffee per day. But the research is also clear that coffee drinkers can develop tolerance against the diuretic effects of caffeine.

So what’s the bottom line? The old wives’ tale that coffee causes dehydration just doesn’t hold a lot of weight. Contrarily, moderate amounts of caffeinated beverages can actually contribute to the body’s daily water needs. Instead, you should steer clear of excessive coffee drinking.


Are you dehydrated?

Are you at risk?
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