Last week, as I stared at my dry, dull face in the mirror, I proclaimed to my boyfriend that the two cups of coffee I'd downed that morning had really dried me out. He scoffed. “Coffee doesn’t actually dehydrate you—that’s a myth,” he responded, casually tossing a grenade into my entire belief system.
Um, excuse me, what? Of course coffee dehydrates you. Of course caffeine dries out your skin, gives you headaches, and causes you immense guilt for choosing cold brew over cold water. Right?! Wrong. After a quick Google search and a flip through my rolodex of doctors, I discovered that my dude was actually correct: Caffeine doesn’t dehydrate you.
Well, at least not in the intense, dramatic way we all think. “Coffee, or, specifically the caffeine in coffee, does have a diuretic effect—meaning it causes your kidneys to flush extra water through urination—but the stimulant is very mild,” says Jennifer Haythe, M.D., a cardiologist and internist at Columbia University.
Basically, chugging a bunch of caffeinated drinks can cause you to pee more frequently, which is technically dehydrating (since you’re losing some fluids), but it won’t be enough to impact your body’s water volume. “In a healthy body, it’s very unlikely that a few cups of coffee are the cause of your dull skin, or headaches, or overall feeling of dryness—at least, not through the mechanism of dehydration,” says Dr. Haythe.
Plus, because you’re ingesting that caffeine with a volume of fluid (like tea and coffee), you’re offsetting any liquid lost through urination. In fact, one 2014 study even found that drinking coffee (in moderation) caused such minimal diuretic effects, that it actually hydrated study participants, rather than dehydrated them.
Pretty awesome, right? Of course, not all people will feel great after a venti blonde roast. Some people may just have a sensitivity to caffeine, which can trigger headaches or stomachaches, but it’s very unlikely that’s because of dehydration. “There are dozens of reasons why someone could feel crappy,” says Dr. Haythe.
And the bottom of that long, long list? Your morning caffeine. Please celebrate this joyous news by drinking a jug of iced coffee on me.
This story was updated on July 2, 2019, to clarify research details.
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