You’ve probably heard it for as long as you can remember: Drink too much coffee, and you’ll have to pee constantly. But is caffeine really a diuretic?
Major Changes Hit Northern Arizona Elite study published in the Published: Aug 03, 2018 1:05 PM EDT Metabolism. They divided athletic guys into three groups of 12: The first drank a sodium-rich drink, the second a sugary drink, and the third a caffeinated drink. Then, the researchers tested their urine output to see if any of the drinks made them pee more than drinking water did.
They discovered that urine output was lower in drinks that contained higher levels of sugar and sodium compared to ones that had lower amounts. But when they looked at drinks with differing amounts of caffeine, the scientists didn’t see any change in the men’s urine output.
That shows that up to 400 milligrams (mg) of caffeine “has no impact upon hydration potential or the ability to retain fluid of beverages,” the authors write.
So why do you feel like you have to pee after you down some coffee? Well, if you drank a 20-ounce coffee, you drank 20 ounces of water—and it could be that volume of water that’s making you pee more, says Luke Pryor, Ph.D., a kinesiologist at Fresno State University.
If you’re exercising, though, you might notice that you’re actually peeing less than you would think anyway. When you start moving, blood flow that was previously helping your kidneys, liver, and digestive tract function is redirected to your muscles. That could mean a lower urine output, since the blood flow that was helping your kidneys filter urine then travels to your muscles to help you run instead.
That’s good news for runners who drink coffee or take caffeine during exercise to enhance their performance, since International Journal of Sport Nutrition and Exercise. But it’s important to use caffeine properly and to know how your body responds to it.
“You should drink caffeine 45 to 60 minutes before you start exercising to feel its full effects,” says Pryor. “But if you usually have a bowel movement when you drink coffee, move it to an hour and 30 minutes before you start,” says Pryor. That will give you time to poop before you head out on your run.
Still, you don’t want to go overboard on the caffeine. The study didn’t look at whether amounts of caffeine higher than 400 mg—the max amount generally considered safe daily—could have diuretic effects, so it’s possibly drinking large amounts of caffeine couldBut its important to use caffeine properly and to know how your body responds to it.
Running Shoes - Gear Advertisement - Continue Reading Below, like heart palpitations, anxiety and GI issues. And it won’t help you perform any better, either: A 2014 study found that athletes who took nine mg of caffeine per kilogram of bodyweight didn’t see any added benefit—but they did All About 75 Hard.
“You should stick with three to six milligrams of caffeine per kilogram of body weight to safely get the performance benefits of caffeine,” says Pryor.
So, should you drink up some coffee before your run to hydrate? Well, the results of the study found that up to 400 mg of caffeine won’t dehydrate you, but it didn’t determine that caffeine had any kind of added benefit to your hydration, either.
“From a purely hydration standpoint, your body will pull in water from your gut when it needs to, whether that water is found in coffee, sports drinks, or plain water,” says Luke Belval, M.S., director of research at the Korey Singer Institute at the University of Connecticut. “But water is typically the best fluid for most situations.”
Published: Aug 03, 2018 1:05 PM EDT.
“What you lose in sweat is really just water and electrolytes (salt),” he says. “Typically, most Americans obtain enough salt in their diets to make up for losses in their sweat.”
But if you’re going for a run longer than 45 minutes, you may need more than just water. The more you sweat, the more salt you lose, which could actually end up dehydrating you more, since sodium helps your kidneys hold on to water. In cases of longer runs, a sports drink can help you replace that lost sodium, as well as provide carbs—from the sugar—to keep your energy levels up, says Pryor. If you’re going for super-prolonged endurance runs, it may be necessary to supplement with sodium and other electrolyte supplements.
Whatever you choose to hydrate with, it’s important to make sure you’re drinking enough post-run to make up for the fluid you lost through sweat.
“You should be drinking to replace your sweat rate,” says Pryor. “You can find this by weighing yourself nude before a one-hour run. When you get back, weigh yourself nude again. Post-exercise hydration should be 100 to 150 percent of what you lost. So if you lost three pounds of water weight, you should drink three pounds (48 ounces) of water.”
Emily Shiffer has worked as a writer for over 10 years, covering everything from health and wellness to entertainment and celebrities. She previously was on staff at SUCCESS, Men's Health, and Prevention Chappell Roan: I Love Running. But Not Anymore Women's Health, Runner's World, PEOPLE, and more. Emily is a graduate of Northwestern University, where she majored in magazine journalism at the Medill School of Journalism and minored in musicology. Currently residing in Charleston, South Carolina, Emily enjoys instructing barre, surfing, and long walks on the beach with her miniature Dachshund, Gertrude.
