Hyponatremia in Athletes Sports

INTRODUCTION On Sunday, December 2, 2001, in the comic section of the Chicago Tribune, the Peanuts comic strip dealt with hyponatremia. Team doctor Snoopy trotted out onto the field and deduced that Woodstock was suffering from hyponatremia. Snoopy correctly determined that this electrolyte imbalance could be corrected by the right combination of water and salt. Woodstock was allowed to drink the water, but Snoopy sprinkled the salt on his feathers. In this case, comic license overruled good medical practice, although Woodstock evidently survived Snoopy’s inappropriate treatment. That such a rare disorder was featured in a popular comic strip attests to a growing interest in the topic among the general public as well as among sports health professionals. That hyponatremia can prove fatal to otherwise healthy athletes is reason enough for sports health professionals to be aware of what the risk factors are and how the disorder can be prevented. Although the incidence of fatal hyponatremia is rare, case reports and descriptive data suggest that non-fatal hyponatremia may be common. Estimates of the frequency of hyponatremia associated with prolonged exercise (e.g., marathons and Ironman-distance triathlons) span a wide range, in some cases exceeding 30% of the athletes tested (O’Toole et al., 1995). However, data from the US military indicate an incidence of hyponatremia of only about 0.10 per 1,000 soldier-years (Craig, 1999), far below the rates reported in athletes (Davis et al. 1999; O’Toole et al., 1995; Speedy et al., 1999). The wide disparity in incidence rates may partly reflect differences in case finding and severity. For example, studies on athletes often use a subset of race entrants, those seen in the medical tent. Some of these athletes have only mild hyponatremia and no clear-cut symptoms from it. Incidence statistics from the military and some studies on athletes key on hospitalized cases, so mild cases of hyponatremia could be missed. We need to study larger cohorts of athletes to better characterize the risk of hyponatremia. Still, the current data warrant that medical personnel consider hyponatremia as a possible cause of collapse during or following prolonged exercise.