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Attention marathon runners: Only drink when you’re thirsty

A runner grabs cup water mile 12 Chicago Marathon.

A runner grabs a cup of water at mile 12 of the Chicago Marathon.

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Updated: February 6, 2012 4:30PM



Attention runners: Only drink when you’re thirsty.

It’s simple, but potentially life-saving, advice many runners do not heed, according to a study by doctors at Loyola University Medical Center that found nearly half of recreational runners might be drinking too much during races.

Drinking too much fluid, regardless of whether it’s water or a sports drink, can dilute the sodium content in the blood to dangerous levels, causing a condition known as hyponatremia.

After surveying 197 runners, researchers found 55.7 percent drank water and sports drinks during races when thirsty, 36.5 percent drank at pre-scheduled intervals and 8.9 percent drank as much as possible.

Hyponatremia affects mostly people who run for more than 60 or 90 minutes, said Dr. George Chiampas, medical director for the Bank of America Chicago Marathon on Oct. 9.

Symptoms of hyponatremia vary, but include confusion and swollen fingers.

“Slow-running women are at higher risk,” said Dr. James Winger, who headed the study. “It could be they’re simply on the course longer, or planned to drink more,” Winger said.

“Establishing a pre-race hydration plan could also be a risk factor,” Winger said.

“Drinking when you’re thirsty is the only way that’s been scientifically shown not to put you at risk of low blood sodium and give you every benefit of performance,” Winger said.

Chiampas also promotes the drink-to-thirst philosophy and notes runners should ignore those who advise marathoners to start hydrating days in advance because of hot race-day temperatures.

“It is a harmful message. Runners start filling up their tank with fluids and by race time they’ve already dropped their sodium levels and put themselves in a position where they could become hyponatremic that could have been easily avoided,” Chiampas said.

However, Midwestern running guru and author Hal Higdon, whose marathon training guide is gospel to many a novice runner, does not think thirst is always the best signal.

“Sometimes the body isn’t smart enough to do that. You need to experiment with different amounts and different types of fluids while training,” said Higdon. “You’ll know if you’re overhydrating because you’ll be spending too much time in the bushes or portable toilets. It’s a learned experience, like learning to love asparagus,” he said.

In recent years, there have been 12 documented and eight suspected runners’ deaths from hyponatremia, according to physiologist Lara Dugas, a co-author of the study.



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