Heat-related dehydration is a big problem in summer. And if you're active — even if you're healthy — you're at risk. Thirst isn't always the best clue that it's time to take a drink.
Technically, dehydration sets in when a person has lost 2 percent of his or her body weight. How quickly that happens depends mainly on the conditions.
The American College of Sports Medicine recommends that athletes drink 16 ounces of fluids — two full glasses — a couple of hours before starting practice or exercise.
Duke University sports medicine expert Blake Boggess says the body needs that much time to absorb the fluid.
For most adults, thirst is a good guide that it's time to take in some fluids, he says. But research suggests that by the time we have reached our late 30s, our recognition of thirst has become a bit delayed.
That means weekend hikers or bikers should drink up before they venture out.