Coffee is a go-to morning beverage for most Americans—but is your cup of joe messing with your hydration?
Across forums online and in everyday life, you might hear people advise coffee drinkers to grab a glass of water before or immediately after having their morning brew. The goal is to stave off any coffee-induced dehydration.
Adding in an extra glass of water can’t hurt—and it’ll certainly help you get one step closer to hitting your daily hydration goals. But experts say the fear that coffee causes dehydration is, in most cases, unfounded.
The notion that coffee is dehydrating is a myth, albeit a long-standing one.
All the way back in 1928, researchers published a study concluding that coffee had a diuretic effect, making participants urinate more. That’s something most coffee drinkers have likely experienced themselves.
But it’s not limited to just coffee—any sort of caffeinated drink, including tea, energy drinks, or soft drinks, can make people urinate more, Julie Stefanski, MEd, RDN, senior editor for Foods & Nutrition at Goodheart-Willcox and spokesperson for the Academy of Nutrition and Dietetics, told Health.
So it makes sense why people may assume that drinking caffeinated drinks such as coffee would leave their bodies more dehydrated than when they started.
However, although coffee works like a diuretic, its effects aren’t particularly long-lasting.
Even back nearly 100 years ago, researchers found that regular coffee consumption could help people could build up a tolerance to these diuretic effects. And that finding has been replicated numerous times in the years since.
In 2005, researchers had male participants consume caffeine for six days, then split them into high, low, and no caffeine groups for an additional five days. All participants had similar urine output throughout the trial.
Similarly, a 2014 study enrolled 50 male coffee drinkers—over the course of three days, participants either drank four cups of coffee or water daily (in addition to a standardized water intake). The results showed no differences in hydration status among the participants.
When you consume caffeine—whether from coffee or any other caffeinated beverage—it affects how your kidneys process both salt and water, said Theresa Gentile, MS, RD, a Brooklyn-based dietitian and spokesperson for the Academy of Nutrition and Dietetics.
Specifically, caffeine causes the kidneys to filter more fluid, prevents them from reabsorbing normal amounts of sodium, and can even disrupt certain signals between the liver and kidneys, Gentile told Health. All of that means “losing more urine and salt,” she explained.
But as your body adjusts to caffeine over time, those effects largely go away, Gentile said.
Once that happens, moderate caffeine intake shouldn’t cause dehydration—in fact, coffee is mostly water and will even count toward your daily fluid needs, she explained.
You shouldn’t experience any issues with dehydration if your caffeine intake stays consistent, but any time you’re consuming more caffeine than your body is used to, expect to take more trips to the bathroom, Gentile added.
In particular, she explained, very high amounts of caffeine—think five or more cups of strong coffee or several energy drinks—can “cause a stronger diuretic effect,” even for regular coffee drinkers. At that point, or anytime you significantly increase your daily caffeine intake, you could be at risk for dehydration, Gentile said.
For most adults, limiting caffeine consumption to 400 milligrams per day—about two to three 12-ounce cups of coffee—is an amount “not generally associated with negative effects,” according to the Food and Drug Administration (FDA). For most people, staying beneath that limit shouldn’t lead to any hydration issues either, Gentile added.
Beyond that threshold, though, higher doses could raise your risk of dehydration, as well as:
But when it comes to coffee consumption, what’s healthy looks different for every person. “There is wide variation in both how sensitive people are to the effects of caffeine and how fast they eliminate it from the body,” per the FDA.
So if you’re a new coffee drinker (maybe the ads for pumpkin spice lattes finally got to you), your body may not be used to caffeine. It’s smart to start with a smaller dose—maybe 50 to 100 milligrams—and see how your body responds, Gentile recommended.
Plus, anytime you’re drinking caffeine, it’s important to pay attention to your body and make sure you’re well-hydrated.
“A general rule of thumb that’s often taught to athletes is that you should be peeing at least every three to four hours and the urine should be light yellow or clear,” Joseph Vassalotti, MD, clinical professor of nephrology at the Mount Sinai Icahn School of Medicine and the Chief Medical Officer of the National Kidney Foundation, told Health.
Any darker or less frequent urination—coupled with other dehydration symptoms such as headache, dry lips, muscle cramps, or lightheadedness—may mean it’s time to put down the coffee and grab a glass of water.
