There's a belief that one of the most popular beverages in the world is also a diuretic. If you're a coffee drinker, this is what you need to know before your first sip.
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There are two types of people in the world: people who start every day with coffee, and people who just don't get what the big deal is about the bean juice. If you fall into the former camp, you've probably heard all kinds of mixed messages about your coffee habit—that it might help you live longer but could temporarily raise blood pressure, or that it can lower your risk of various chronic diseases but can also mess with your sleep. Some people even worry that coffee causes inflammation.

Perhaps you've also heard the warnings that coffee is dehydrating. But, is it? And if it is, how worried should you be? To set the record straight on whether coffee is a diuretic, we asked two registered dietitians to weigh in.

Is Coffee Dehydrating?

The answer is yes and no. Spoiler alert: Experts say that, overall, coffee is not actually dehydrating. "The caffeine in coffee does have a diuretic effect, meaning it makes your kidneys produce more urine," says Sarah Curry, M.S., RD, a dietitian based in the U.S. and the U.K. who specializes in eating disorders and irritable bowel syndrome. "The good news for coffee lovers is, the effect is only a minor one."

That's because you're likely consuming more liquid than you're losing when you drink a cup of coffee. "The diuretic effect of coffee is pretty insignificant, and it's actually counterbalanced by the fact that coffee is mostly water," says Beth Stark, RDN, LDN, a nutrition and culinary communications consultant based in Pennsylvania. "So you end up with positive hydration when it's enjoyed in moderation."

How Much Coffee Is Safe to Consume?

According to the U.S. Food & Drug Administration, healthy adults can consume 400 milligrams of caffeine per day, the amount found in four to five (standard 8-ounce) cups of coffee. (Note that's a "short" at Starbucks; a "tall" is 12 ounces).

However, there are multiple factors at play that determine how much is right for you. Everyone reacts to caffeine in their own way. Side effects of consuming too much caffeine (which can happen even within the 400-mg guidelines) include insomnia, jitters, anxiousness, gastrointestinal distress, headaches and mood problems, according to the FDA. If you experience those, consider cutting back.

In addition, you may also have to limit caffeine if you have high blood pressure, heart disease, anxiety or are pregnant, Curry says. This has little to do with hydration and more to do with the stimulating effects of caffeine, she says.

Keep in mind that caffeine content differs depending not only on the size of the cup but also on the roast and type of coffee drink you're consuming. Buying coffee from a coffee shop may be more potent than at-home coffee drink creations. "Caffeine content is often higher in coffeehouse drinks like cold brew, cappuccino or lattes [compared to home-brewed cups], so be mindful if you're drinking coffee outside of the home," Stark says. The strength of cold brew can vary greatly depending on the amount of coffee grounds that are used and how long they're steeped. And coffee drinks may have multiple shots of espresso. Each 1-ounce shot of espresso in a coffee drink contains about 63 milligrams of caffeine.

What Should You Do If Coffee Makes You Feel Dehydrated?

"If we look at the research, you are not likely to become majorly dehydrated from drinking coffee," Curry says. Past research, published in PLOS One, on 50 male coffee drinkers found that there wasn't a difference in hydration whether they were drinking coffee or water. The researchers concluded that coffee was similarly as hydrating as H20. (Though, that's not your cue to skip water entirely!)

Yet, research isn't absolutely indicative of how every person reacts to coffee (or anything else), so if you feel like coffee makes you feel thirsty and dehydrated, Curry recommends honoring that. "You may find you feel more refreshed starting the day with a glass of water before you kick off your coffee routine," she says.

It's also possible that you're dehydrated for other reasons and that coffee is just a small part of the equation. For example, being in a hot climate and sweating more, plus not drinking enough water and consuming a lot of caffeine could all combine to lead to dehydration. "Signs of minor dehydration are tiredness, dry mouth or lips, headache, thirst, dry skin, constipation and dark yellow or strong-smelling urine," Curry says.

"At the first onset of these symptoms, drink some water or a sports drink and monitor closely to see if symptoms improve," Stark says. "This is typically effective for most people that experience mild dehydration from simply not drinking enough fluid." But if those symptoms persist, call your doctor or visit the emergency room immediately.

The Bottom Line

While the caffeine in coffee does have a mild diuretic effect, you're actually drinking more fluid than you're losing when you drink a cup of the stuff. Of course, anything can have negative side effects if you go overboard, so stick to no more than 400 milligrams of caffeine (about four to five 8-ounce cups of coffee) per day. Consider cutting back if you're experiencing symptoms like irritability, insomnia or dehydration.