Are You Overhydrated?

You've heard it since you were a kid, from your parents to your gym teacher: Drink two liters (or eight glasses) of water every day. Lately, though, researchers have been questioning the tried-and-true water rule, and in fact, believe even health-minded individuals could be drinking too much H2O.

“There’s no scientific method behind those numbers,” says exercise physiologist Stacy Sims, Ph.D., a hydration researcher at Stanford University. “And the recommendation doesn’t take into account gender, environment, altitude, fitness level—factors that could affect fluid intake needs.”

In fact, there’s a lot of marketing behind popular hydration recommendations, Sims says—with potentially dangerous consequences. “Drinking too much fluid can lead to hyponatremia, which is when sodium in blood becomes too diluted,” Sims says.