Myth #5: Coffee dehydrates you
You've probably heard that caffeine, like alcohol, is a diuretic that causes the kidneys (in a different way than alcohol) to allow extra water out when you pee. But recently, a well-regarded study in the UK showed that a moderate amount of caffeine doesn't seem to dehydrate you. Regular coffee consumers spent four days drinking four cups of coffee per day and four days drinking a caffeine-free placebo, and researchers measured how hydrated they were. Joe addicts clinked mugs when the findings came in: They were equally hydrated, regardless of caffeine consumption.
Good to know, but it's also worth keeping in mind that while results were statistically significant, they came from only 50 male participants who were already used to drinking three to six cups daily. They also lived in the not-so-sunny UK and weren't allowed to work out or drink alcohol. Eliminating other causes for extra water loss was how the researchers made this a controlled trial, but it doesn't describe most of our lifestyles -- there was no chance to see how coffee, exercise, and drinking might act together.
Moral of the story? A cup or two shouldn't be an issue, but don't go trading your water bottle for an insulated mug.
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Marina Komarovsky is a freelance writer for Thrillist, and she was never willing to believe that coffee was bad for you in the first place. For more on water and food and such, follow her tweets: @MariKomarovsky.