Exertional Hyponatremia Among Active Component Members of the U.S. Armed Forces, 2007-2022

Exertional hyponatremia occurs either during or following periods of heavy exertion, when losses of water and electrolytes due to the body's normal cooling mechanisms are replaced only with water. Hyponatremia can lead to death or serious morbidity if left untreated. Between 2007 and 2022, there were 1,690 diagnoses of exertional hyponatremia among active component service members, for an overall incidence rate of 7.9 cases per 100,000 person-years (p-yrs). Those younger than 20 years or older than 40, non-Hispanic White service members, Marine Corps members, and recruit trainees had higher overall rates of exertional hyponatremia diagnoses. Between 2007 and 2022, annual rates of incident exertional hyponatremia diagnoses peaked (12.7 per 100,000 p-yrs) in 2010 and then decreased to a low of 5.3 cases per 100,000 p-yrs in 2013. During the last 9 years of the surveillance period, rates fell between a range of 6.1 and 8.6 cases per 100,000 p-yrs. Service members and their supervisors must know the dangers of excessive water consumption and prescribed limits for water intake during prolonged physical activity, such as field training exercises, personal fitness training, as well as recreational activities, particularly in hot, humid weather.