Does coffee actually cause dehydration?


Chances are, you’ve heard that coffee is dehydrating. This notion has been floating around for ages. But given how popular (and, honestly, life-giving) coffee is, the claim warrants some investigation. Do you really need to worry that you’re dehydrating your body bit by bit with every sip of coffee? Here’s the deal.

In news you already know, coffee contains caffeine. If you’ve ever wanted to bow down to coffee after it’s gotten you through an exhausting day, you’re aware that caffeine is a stimulant. But the caffeine in coffee can also act as a diuretic, according to the US National Library of Medicine. This means it might make you pee more than you normally would.

Diuretics generally cause your body to expel sodium and water, the Mayo Clinic says. Scientists aren’t yet totally sure how caffeine does this. It may have something to do with how caffeine physically affects the kidneys through mechanisms like lowering sodium reabsorption, meaning there’s more salt for your body to expel via your urine. As it happens, sodium pulls water from your blood on its way out of your body, the Mayo Clinic says, so this can result in an uptick in pee. Another theory holds that caffeine acts as a diuretic by working on receptors for the neurotransmitter adenosine in a way that changes your body’s sodium and fluid balance. (Keep in mind this is about the caffeine—so if you’re drinking decaf, this diuretic effect won’t be nearly as intense.)

So, yeah, the bottom line is that you might need to take more bathroom trips than usual when you’re drinking a lot of coffee. How true this is can vary from person to person. Some research points to this diuretic effect being strongest in people who don’t regularly drink caffeine, then have high amounts of it. But, of course, if your morning drink is a 16-ounce iced coffee, then keep in mind that you’re drinking a ton of liquid and will clearly need to pee after that.

Since coffee is still a liquid, its hydrating properties can basically balance out its diuretic effects, which should stave off dehydration, according to Colleen Tewksbury, PhD, a senior research investigator in the Perelman School of Medicine at the University of Pennsylvania.

Everyone’s body handles caffeine differently, of course. But, in general, coffee is “roughly equally hydrating as it is a diuretic,” Dana Hunnes, PhD, adjunct assistant professor at the UCLA Fielding School of Public Health, tells SELF. This is part of why how much water you should drink every day is such an individual thing. Fluids from beverages such as coffee are hydrating, so they count, too.