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Fitness Cardiovascular

Can Drinking Too Much Water Sink Runners?

Summary & Participants

While dehydration is a common concern for runners, especially during a marathon, experts now say that too much water can be worse. Learn the right way to stay hydrated.

Medically Reviewed On: July 06, 2008

Webcast Transcript

ANNOUNCER: Our bodies need water in order to function properly. And when exercising, we primarily lose water through sweating. And while dehydration is a common concern for runners, the role and impact of hydration is largely misunderstood.

LEWIS G. MAHARAM, MD: The body's made up of water. And in order for muscles and your bodily physiological functions to work, you need to have fluid in your body. But grandma made this a much bigger deal than it is for runners and people that are athletic.

Grandmas used to tell you to drink, drink, drink, drink, drink, drink, drink when you go out and exercise in the heat, but research has shown that that's really not necessary.

ANNOUNCER: In fact, there is no sound scientific evidence that supports the idea that dehydration is a significant danger for runners.

LEWIS G. MAHARAM, MD: Dehydration is caused by staying out in a desert for a long period of time. Dehydration is not an issue when running a race.

It's not an issue because it doesn't happen. Dehydration doesn't happen when you run a race of any distance.

ANNOUNCER: Dehydration means your body does not have as much water and fluids in it as it should. And while the body does lose fluids when running, most people simply do not run long enough for dehydration to be dangerous. Increasingly, the reverse problem arises, where runners drink too much, causing a condition known as hyponatremia.

LEWIS G. MAHARAM, MD: Hyponatremia is when your serum salt level is below a specific number in the blood.

When the salt level drops, initially, you become dizzy, faint, your sensoria may change. You then may have some nausea, vomiting, diarrhea. You also may have some syncope; that's fainting. Seizures, your brain starts to swell, you get pulmonary edema, and then eventually your brain stem will herniate and die if the serum sodium gets too low.

We're finding that hyponatremia in exercise happens most often, to runners and walkers that are out there on the course for long periods of time that stop at every water station along the course and drink like grandma told them to, drink, drink, drink, drink, drink. And if they stop at every water station along the course at these events, they end up getting hyponatremic.

So, how can runners estimate their fluid needs?

LEWIS G. MAHARAM, MD: Moderate to elite exercisers or even weekend exercisers don't need to estimate what their fluid needs are. That's another myth that is going by the wayside. Research shows that all you need to do is either drink for thirst or drink no more than one cup, eight ounces of a sports drink every twenty minutes while out exercising, but no more than that.

If you drink for thirst, the new research shows, then you're drinking plenty.

ANNOUNCER: So, where did the idea that we need to constantly hydrate during exercise come from?

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