Update: Exertional hyponatremia, active component, U.S. Armed Forces, 2006-2021.

From 2006 through 2021, there were 1,669 incident diagnoses of exertional hyponatremia among active component service members, for a crude overall incidence rate of 7.8 cases per 100,000 person-years (p-yrs). Compared to their respective counterparts, female service members, those less than 20 years old, and recruit trainees had higher overall incidence rates of exertional hyponatremia diagnoses. The overall incidence rate during the 16-year period was highest in the Marine Corps, intermediate in the Army and Air Force, and lowest in the Navy. Overall rates during the surveillance period were highest among non-Hispanic White service members and lowest among non-Hispanic Black service members. Between 2006 and 2021, crude annual incidence rates of exertional hyponatremia peaked in 2010 (12.7 per 100,000 p-yrs) and then decreased to a low of 5.3 cases per 100,000 p-yrs in 2013. Crude annual rates fluctuated between 2016 and 2021, reaching the highest rate in 2020 (8.3 per 100,000 p-yrs) and then decreased to 6.8 per 100,000 p-yrs in 2021. Service members and their supervisors must be knowledgeable of the dangers of excessive water consumption and the prescribed limits for water intake during prolonged physical activity (e.g., field training exercises, personal fitness training, and recreational activities) in hot, humid weather.