Does Coffee Dehydrate You? A Urologist Reveals the Truth

Updated: Nov. 14, 2023

A doctor sets the record straight on one of the widest-believed alleged downsides of your morning cup: That coffee depletes your system of water.

Coffee addict? Wake up and smell the coff—oh wait, your day started strong, right? If you’re like many Americans, you’ve probably already downed a couple cups of Joe—and we do mean many Americans: 70% of US adults say they drink coffee every week, while 62% report drinking it daily, according to a 2023 survey done by the National Coffee Association of America.

However, while coffee has many fans, there is one big potential drawback. Coffee sometimes gets a bad rap as being unhealthy for one main reason: It’s dehydrating. Does your beloved beverage deserve such defamation? A urologist spilled the beans to The Healthy @Reader’s Digest.

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Diuretic vs. dehydration

A lot of the confusion stems from a misunderstanding about what caffeine does in your body, says S. Adam Ramin, MD, a Los Angeles-based urologist and medical director of Urology Cancer Specialists. “Caffeine is a mild diuretic, meaning that it increases your need to urinate, so in that sense you are losing more water than if you hadn’t had any coffee,” Dr. Ramin explains. “However, just because something is a diuretic doesn’t mean it will automatically dehydrate you, and the effect in this case is slight. Coffee is mostly water, so you’re replacing what you lose.”

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What the science says

A meta-analysis (a research paper that examines multiple studies on the same subject) published in the peer-reviewed journal PLoS One concluded that “coffee, when consumed in moderation, provides similar hydrating qualities to water.” A finding in part of this research was that adults who drank between three and six cups of coffee a day showed no difference in hydration—as shown by measuring markers both in blood and urine—compared those who drank the same amount of plain water.

To the question “Does coffee dehydrate you?” adds Amanda A. Kostro Miller, RD, a licensed dietitian nutritionist in Nashville, TN: “In the past, people were often advised to avoid drinking coffee if they wanted to stay well hydrated, but this is a myth.” Better yet? “You can count coffee toward your daily hydration goals,” this nutrition expert says.

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Coffee should not replace water

While coffee can be hydrating, it doesn’t mean that you should drink it as your only source of hydration, say our experts. If you drink coffee to the exclusion of water, it can hurt your health, making you jittery, anxious and disrupting your sleep.

“I don’t recommend using coffee as your main source of hydration, as too much coffee can harm your kidneys,” Dr. Ramin says. “It can increase your risk of kidney stones due to its high oxalate content and make symptoms of an overactive bladder worse.”

The Healthy @Reader’s Digest’s Medical Review Board co-chair Latoya Julce agrees, emphasizing your kidney could be in danger if you’re consuming more caffeine than water. “Dehydration can cause a build-up of wastes and acids in the body, and it can clog the kidneys,” she explains.”

The key, says Kostro, is moderation. “The Dietary Guidelines for Americans recommends limiting caffeine to 400 milligrams per day, which is about three to four cups of coffee,” she says. “After that, I recommend switching to water.”

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