What is hyponatremia? How is it involved with hydration/dehydration? How can it be avoided?
Simply put, hyponatremia is when serum sodium levels become too low. Clinically, hyponatremia is typically the result of some other more serious condition that interrupts the body’s normal thirst, ADH, aldosterone or renal function. Since most questions on this site relate to exercise and athletics, I will spare the reader the grueling intricacies and clinical jargon and limit our discussion to hyponatremia related to prolonged exercise, leading to significant sodium losses, and excessive fluid consumption (also called water toxicosis). For most exercisers, the importance of adequate hydration is well known. Dehydration by even a small amount can have a tremendous impact on an athlete’s performance. Evidently coaches and the media’s warnings have been headed. Many athletes, especially those involved in ultraendurance events, are consuming too much water. Hyponatremia has also been observed in summertime hikers in the Grand Canyon and in the military. The Armed Forces looked at the issue after their medical examiner in Rockville, Maryland received several cases that involved excessive water intake resulting in three deaths. The rapid increase in total body water (TBW) increases the extracellular fluid, leading to edema. For most tissues this is not an issue, but for the brain, with it’s limit space for expansion, this edema can lead to hemorrhage, coma and death. Symptoms of hyponatremia include:
Risk factors for the development of hyponatremia during extreme endurance events include excessive fluid consumption during and after exercise, female gender, NSAID use and slower race times. There was also an inverse relationship between event weight loss and development of hyponatremia. Those with hyponatremia do not always present with obvious symptoms, though disorientation and seizure are strong indicators. If an athlete experiences any of the above symptoms, seeking medical attention quickly is the wisest idea, as the consequences can be deadly.
So, how can an athlete prevent hyponatremia? If pure water is to be used, sticking to the lower end of the American College of Sports Medicine’s (ACSM) intake recommendation (20-30 oz./hr) may be a good idea. The simplest remedy would be the use of sports drinks (Gatorade, Powerade, etc.) rather than pure water for hydration in ultraendurance athletes. In addition to providing fluid, sodium and other electrolytes, they supply performance-maintaining carbohydrate. Thanks for a very good question. I learned a lot researching it.
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- Davis DP, Videen JS, Marino A, Vilke GM, Dunford JV, Van Camp SP, Maharam LG. Exercise-associated hyponatremia in marathon runners: a two-year experience. J Emerg Med 2001 Jul;21(1):47-57.
- Speedy DB, Noakes TD, Rogers IR, Thompson JM, Campbell RG, Kuttner JA, Boswell DR, Wright S, Hamlin M. Hyponatremia in ultradistance triathletes. Med Sci Sports Exerc 1999 Jun;31(6):809-15.