Does Drinking Coffee Really Dehydrate You? We Asked Dietitians

It's not as detrimental to hydration as you might think.

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 sip more coffee than 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 and 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.

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Regular Coffee Drinkers

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. While coffee itself isn't too dehydrating, some frequent coffee drinkers should still hydrate in other ways.

"Don't let your caffeine intake impair your intake of straight fluids like water," Nussbaum says. Coffee may not dehydrate you detrimentally, and it can even count toward your daily hydration—but it's still imperative to drink enough water (and other more hydrating drinks) throughout the day.

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Casual Coffee Drinkers

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 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, but it certainly has less of a diuretic effect than caffeinated.

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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. And 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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  1. National Coffee Association, NCA releases atlas of American coffee.

  2. Killer SC, Blannin AK, Jeukendrup AE. No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population. PLoS One. 2014;9(1):e84154. doi:10.1371/journal.pone.0084154

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