Whether you are on the high school track team or you’re training for your first marathon, you’ve probably been following the same advice: Hydrate, hydrate, hydrate. For years, runners have been told, especially when training during the summer months, to drink “plenty” of water.
Your resting metabolic rate (RMR) is the amount of calories you need to maintain energy. Yet a recent study published in the New England Journal of Medicine proved that “plenty” is an arbitrary term. The study showed that when athletes drink too many fluids without ingesting foods during prolonged endurance activities (three-four hours), the result could be fatal.
Studying 488 runners in the 2002 Boston Marathon, researchers found that 13 percent of them drank so much during the race that they ended up with a condition known as hyponatremia.
Hyponatremia results when the concentration of sodium in the blood gets too low. When athletes, such as marathon runners, exercise in extremely hot weather, they often drink more water than their kidneys can excrete. That extra water moves into their cells, including their brain cells, which may impede their brain stem’s ability to function.
Severe hyponatremia is relatively uncommon but can be deadly (three runners in the study were found to be in danger of dying), so all endurance athletes should be careful to understand the problem and take precautions.
Symptoms of Hyponatremia
Symptoms can include fatigue, nausea, vomiting, cramps, dizziness, headache, poor exercise endurance and sleepiness. If you’re feeling any of these symptoms, contact a physician or – during a race – go to a medical aid station.
Minimize Your Risks
1. Avoid taking NSAID drugs (Nonsteroidal Anti-Inflammatory Drugs) such as Ibuprofen and Naprosyn before a race, backpacking trip or long day hike. These drugs can influence your kidneys’ handling of water and sodium and can contribute to kidney damage if you become dehydrated.
2. For events and activities lasting longer than three hours, drink fluids that have a mix of carbohydrates, water and electrolytes.
3. If you are in a race, drink small amounts of fluid (3-5 oz) every 20 minutes.
4. If you are hiking or backpacking, eat trail mix, salted nuts or another salty snack in addition to drinking fluids.
While hyponatremia is becoming more well-known, dehydration remains a more common problem. You can avoid both by following these guidelines.
Other Fluid Guidelines:
1. Keep well-hydrated and maintain your weight: Make sure that you don’t gain or lose weight during exercise lasting more than two hours.
2. Drink when you are thirsty and intake small amounts of fluid (3-5 oz) every 20 minutes even if you are not thirsty.
3. Drink enough so that your urine is a light color.
4. Drink fluids one-two hours before your activity or race begins so that you begin the activity well hydrated.
– David Musnick, M.D. is a Sports Medicine and
Internal Medicine physician in Bellevue, Wash.
He is the co-author of Conditioning for Outdoor Fitness:
Functional Exercise and Nutrition for Every Body second edition.
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