At its basic level, hydration is simple. Feel thirsty after a run? Drink something. Heading into an epic meeting? Bring along a water bottle. Despite this simplicity, there's an ocean of misleading information out there that leaves runners confused. Eight glasses a day, or not? Drink before you're thirsty, or only when thirst hits? Does coffee really dehydrate you? Knowing the answers is vital, since hydration is key to your performance. "Water is necessary for every metabolic process in your body," says Penny L. Wilson, Ph.D., R.D.N., a dietitian at Houston's Memorial Hermann Ironman Sports Medicine Institute. "It transports nutrients to your cells and takes waste away from them. It's like oil in a car." We dove below the surface of some myths to uncover the facts and make the truth about hydration as crystal clear as the water you drink.
Myth: Drink eight glasses of water a day.
Truth: You do need a healthy dose of hydration daily, but how much is an individual thing. "The eight glasses a day is totally arbitrary," says Susan Yeargin, Ph.D., assistant professor of athletic training at the University of South Carolina. "Everybody, especially athletes, has different needs." The Institute of Medicine guidelines are more specific, recommending 91 ounces per day for women and 120 for men. But the institute notes that "the vast majority of healthy people adequately meet their hydration needs by letting thirst be their guide."
What and How Much You Should Drink
Myth: Pee clear to be hydrated.
Truth: Clear urine is a bit excessive. "As long as it is a pale yellow, like lemonade, you're hydrated," says Yeargin. If it's completely clear, it just means you're full to the brim; what's going in is coming out. On the other hand, if your pee is the color of apple juice or darker, or particularly smelly, you need to drink up.
Myth: Caffeine dehydrates you.
Truth: While caffeine provides a performance-boosting edge, it also acts as a diuretic, right? Not exactly. "Recent research shows that caffeine doses between 250 and 300 milligrams—about two cups of coffee—will minimally increase urine output for about three hours after consuming it," says Yeargin, "But the research also shows that exercise seems to negate those effects. If you run within one to two hours of drinking coffee, you don't pee more." Most likely, during exercise, blood flow shifts toward your muscles and away from your kidneys, so urine output isn't affected, Yeargin explains. In addition, if you always have a latte in the morning or a soda at lunch, your body is acclimated to the caffeine, so its effect, on both your physiology and performance, is minimal.
Myth: Thirst isn't a good hydration tool.
Truth: Thirst is definitely a very strong predictor of hydration needs—and some experts would argue it's the only one you need. "Our thirst mechanism is pretty accurate," says Yeargin. "But it's always a good idea to have some other methods to ensure you're hydrated." Knowing your sweat rate is one way to track your needs, particularly for long runs, says Doug Casa, Ph.D., professor of kinesiology at the University of Connecticut and COO of the Korey Stringer Institute. To calculate your sweat rate, weigh yourself naked before and after an hour run. Keep track of how many ounces you consume during the run and factor that into your calculation postrun. Every pound you lose translates to about 16 ounces of fluid. "Your goal isn't to match your sweat rate," says Casa, "but you should try to get as close as is comfortably possible. For some runners, that may mean replacing two-thirds of the fluid they sweat during the run." He adds that you shouldn't try to consume more fluids than you've lost.
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