How to stay hydrated during Sunday's marathon

If you are planning to run the Los Angeles Marathon this weekend, get ready to sweat.

Temperatures are expected to reach the 90s Sunday, so runners need to be especially vigilant about staying hydrated.

How hydrated? That depends on how much you perspire, said Glenn Ault, USC professor and medical director of the L.A. Marathon.

"Everyone's a little different," Ault said, but the basic goal is to take in about as much water as you sweat out. 

For the typical marathon runner, that means drinking three to six ounces of water every 15 to 20 minutes, or about one small cup at every other water stop along the course.

However, Sunday may call for a more amped up hydration plan, since higher temperatures mean more perspiration.

"During a hot race you are sweating, which not only means water but salt loss," which can cause sodium levels to drop, leading to fatigue and headaches, Ault said.

To counteract this condition, Ault recommends downing a cup of sports drink every few water stops rather than just pure H2O, since sports drinks contain sodium.

He also recommends that runners consider hitting one or possibly two more stops an hour than they normally would.

Out of the 26,000 L.A. marathon runners each year, a few hundred end up suffering from some form of dehydration, Ault said.

Another tip he suggests for preventing dehydration is to start hydrating a day or two before the race.

However, be careful not to drink too much during a grueling race, said Daniel Vigil of UCLA's School of Medicine. 

"There is such a thing as water intoxication or over hydration," Vigil said.

The official term for this condition is hyponatremia and it occurs when water levels in the body are so high that sodium in the bloodstream becomes dangerously diluted, which can cause heart issues and brain swelling.

Vigil said this condition is relatively rare, but marathon runners who take four hours or more to complete the race may be at the highest risk since they will be drinking the longest.

By taking just one small cup at most water stations, Vigil said, a runner should be OK.