Myth or Fact: Is Coffee Dehydrating?

We look at this common belief and other potential coffee myths.

If you've ever been told to chase your cup of coffee with a tall glass of water, as though it was a shot of tequila, you've heard some version of the old wives' tale that coffee is dehydrating. Despite its diuretic function—the original cause for concern around dehydration—current studies show that coffee hydrates drinkers. Breaking down the science with the help of registered dietitian Amanda Frankeny, I unpack why coffee counts to meet some of your daily fluids needs.

Myth #1: Coffee Is Dehydrating

Meeting your recommended daily fluids may sound intimidating when you hear the numbers; according to the Institute of Medicine, women should be consuming 95 ounces and men 131 ounces daily. Luckily filling your plate can count as well. Hydrating foods like fruits and veggies can help add to your total, so long as most of your fluid intake comes from liquid; juice, sparkling water, tea, and even coffee. According to Frankeny, this is because "those who drink caffeine regularly actually develop a tolerance to the diuretic effects, [referring to] coffee's ability to promote urination."

The FDA advises that adults enjoy no more than 400 mg of caffeine (that includes soft drinks or energy drinks) and that pregnant women limit their intake to 150-300 mg daily. Depending on how you take your coffee (see myth three for more), that's around four cups per day. Any more could cause dehydration, as well as potentially anxiety, insomnia, headaches, and other issues.

Myth #2: It Makes You Pee More

The same chemical that inspires loads of productivity and alertness can also produce more frequent bathroom visits. According to Frankeny, that's because caffeine both increases blood pressure in the kidneys and sends signals to your pituitary gland to stop the production of the antidiuretic hormone. Together this can cause the need to go.

Despite this, studies demonstrate that hydration levels are unaffected, so long as you're consuming the recommended daily amounts of caffeine.

Cup of cappuccino and still water on the table in a coffee shop, side view
Alexander Spatari / Getty Images

Myth #3: Decaf Is Better

A double shot of espresso packs a punch that regular joe just doesn't provide. That's because caffeine levels differ depending on the method and amounts used. Frankeny notes that if you're consuming within your recommended daily limits of 400 mg, whether you enjoy a regular drip coffee in the morning and switch to an espresso pick-me-up in the afternoon, you should be fine.

Myth #4: You Should Drink More Water When You're Drinking Coffee

We've covered that regular java guzzlers have a tolerance for caffeine's diuretic effects and that the brew can even count for some of your daily hydration needs. But if you're still feeling thirsty or are concerned about whether you're getting enough liquids, be alert to some key physical cues. Frankeny shares, "regardless of how much caffeine you drink, look for dehydration symptoms like thirst, weakness, dizziness, fatigue, reddened skin, and dry mouth."

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