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Hyponatremia: What It Is, How to Prevent It
By Courtenay Schurman, MS, CSCS
What Is It
Hyponatremia refers to a low concentration of sodium in the blood and occurs when athletes sweat profusely and then drink copious amounts of pure water to replenish fluids, without adequately replacing electrolytes. It occurs more frequently during endurance events that last longer than several hours, where athletes attempting to rehydrate over several hours of exertion may end up compounding the problem without realizing it. In a study of 36 athletes during a 3-4 hour triathlon and 64 athletes in a 9-15 hour Ironman race, no athletes were hyponatremic following the shorter race, but 27% were hyponatremic and dehydrated following the Ironman.
How Can You Prevent It?
If you plan to be out for a long day’s bike ride or weekend summer climb, the simplest way to prevent getting hyponatremia is to include diluted electrolyte-containing fluids (widely varied, including such drinks as Gatorade, Gukinaid or Powerade) and take plenty of salty snacks including pretzels, chips, nuts, or trail mix. Since salty snacks are known to increase thirst levels, not only will the snacks help you replenish missed salts, they also will encourage you to drink much more frequently.
Sweat contains roughly 3 grams of salt per liter, and the rate of perspiration during a long, hot climb or race can average .5-1 liter per hour. If you are climbing all weekend to the tune of 10-15 hour days, you can easily lose too much salt. Try to replenish sodium at a rate of about 1 gram per hour, as recommended by Doug Hiller, MD at the Hawaii Ironman (www.rice.edu/~jenky/sports/salt.html). Be aware that trying to get the necessary gram per hour from beverage alone would require that you drink two liters of Gatorade each hour – certainly impractical for most people out in the mountains unless you can carry Gatorade powder and continue to add it to your filtered water.
Salty Foods to the Rescue
If you have ever wondered why nuts, soups, trail mix, Doritos, pizza, Mexican food (chips and salsa) or other salty foods taste so delicious during or following long endurance outings, it is because your body needs a certain level of sodium to replace that lost through sweating, and it will tell you in no uncertain terms exactly what it needs. If you or a training or climbing team member experience nausea, muscle cramps, slurred speech, confusion, disorientation, or inappropriate behavior, and yet your urine is clear from your abundant hydration efforts, you may need to get some salt rather than still more water. Severe hyponatremia is a true medical emergency and can result in seizure, coma or even death.