Does Drinking Coffee Really Dehydrate You? We Asked Dietitians

According to the National Coffee Association, 62 percent of Americans drink coffee daily, with the average coffee drinker consuming more than three cups each day. If you tend to spend more time sipping coffee instead of water throughout the day, you might be asking the question: Does coffee dehydrate you? 

"The impact of coffee on hydration is a super common question," says Ilisa Nussbaum, RD, clinical dietitian nutritionist at Yale New Haven Hospital. "We always joke that nutritionists start each answer with 'it depends,' but it's true for this question."

Here are a few ways to figure out exactly how your coffee habit is affecting your hydration levels.

If you're a regular coffee drinker:

If you're concerned about your morning cup of Joe, you need not worry too much. "Anyone who regularly consumes caffeinated coffee or tea will develop a tolerance, and a regular cup of coffee has no real significant effect on overall hydration status," says Marie Spano, MS, RD, CSCS, CSSD.

Studies have shown that drinking two to four cups of coffee (around an 8-ounce size cup—we're not talking Venti here) had little impact on hydration for the regular coffee drinker. The caffeine in coffee is a diuretic, but with regular consumption of coffee, that diuretic effect actually decreases, having minimal impact on urine output.

But don't mistake this information as a free pass not to hydrate in general, it's more a free pass to stop worrying so much about whether coffee really dehydrates you. Where some frequent coffee drinkers may start to feel more dehydrated is when they sip on coffee throughout the day and don't hydrate in other ways

"Don't let your caffeine intake impair your intake on straight fluids like water," Nussbaum says. In short, you still need enough water, you just don't need to overcompensate with water if you drink coffee. Coffee may not dehydrate you detrimentally, and it can even count toward your daily hydration—but it's still imperative to drink enough water throughout the day and other more hydrating drinks.

If you're a casual/occasional coffee drinker:

While the diuretic effect of coffee decreases with regular coffee consumption, the casual coffee drinker may feel more of a dehydrating impact. They simply don't have the same level of tolerance as a more frequent coffee drinker. However, the impact isn't too intense. "In those who don't regularly consume caffeine, drinking two to three cups of coffee will lead to a very short-term and minimal increase in urine output," Spano says.

It's important to pay attention to what you feel like when drinking coffee. For example, if you're taking more trips to the bathroom (for number one or two), you may want to increase your fluid intake to replenish.

And another thing to note—when a habitual coffee drinker goes sans caffeine for a few days, they should treat it more like they're a casual drinker when they come back to it. "If you're sick or recovering from an illness that left you caffeine-free for a few days, it's a good idea to ease back into your coffee habit," Nussbaum says. Of course, whenever you're sick, it's important to hydrate as much as possible.

As for the decaf coffee drinker? Even decaf has trace amounts of caffeine in it, but it certainly has less of a diuretic effect than caffeinated.

Know Your Body

Everyone reacts to caffeine differently and has different hydration needs based on their size, age, and how much they exercise. Two cups of coffee may have little impact on one person, while another will feel more heightened effects. Keep in mind that not all cups of coffee have equal levels of caffeine—if you're noticing a pattern of adverse reactions, it's best to decrease the amount you're sipping.

"The easiest way is to pay attention to what your body feels like when you drink coffee: its impact on your sleep and the number of times you're going to the bathroom," says Nussbaum. 

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