Exercise-induced hyponatremia: causes, risks, prevention, and management.

Exercise-induced hyponatremia is most commonly associated with prolonged exertion during sustained, high-intensity endurance activities such as marathons or triathlons. In most cases, exercise-induced hyponatremia is attributable to excess free water intake, which fails to replete the sometimes massive sodium losses that result from sweating. The risk of hyponatremia can be lowered by strategies to ensure fluid balance during exercise by maintaining the proper volume and type of fluid intake. Treatment of exercise-induced hyponatremia is based on whether the patient is volume-depleted, euvolemic, or fluid-overloaded. Because therapy must be tailored to volume status, physicians must make this determination before initiating therapy. If hyponatremia is life-threatening, hypertonic saline may be warranted to increase sodium in the extracellular fluid compartment and restore the natural balance.