Coffee probably doesn't dehydrate you, after all

We've all heard the warning: Even though coffee is at least 98.5 percent water, that cup of joe you're drinking is a diuretic that will dehydrate you if you don't chase it down with a cup of H20. Well, good news, javaheads — and dedicated tea drinkers, too: Unless you're mainlining the caffeine, coffee and tea are probably about as hydrating for you as an equal amount of water, according to Claudia Hammond at the BBC's Medical Myths blog.

Most of the research underpinning the coffee-as-diuretic idea focuses on the role caffeine plays, and "one of the most frequently mentioned studies was conducted way back in 1928 with a sample of just three people," says Hammond. Here's her theory on why people have believed in diuretic effect for so long:

That doesn't mean you should necessarily drink eight cups of coffee a day (any more than you need to drink eight cups of water), but you probably shouldn't fret too much about that daily pot of coffee dehydrating you, either. --Peter Weber

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