A study reviewing 22 years of data on heat illness hospitalizations and deaths in the U.S. Army indicates soldiers remain at risk for exertional heat illness. While hospitalization rates for heat illnesses have declined over this period, cases of heat stroke have increased.
The research, presented in the August issue of Medicine & Science in Sports & Exercise, the official journal of the American College of Sports Medicine (ACSM), is the largest and most comprehensive epidemiological study of these conditions to date.
From 1980 through 2002, 5,246 soldiers were hospitalized and 37 died from heat-related illnesses, which include heat injury - a mild-to-severe form characterized by organ and tissue injury with high body temperatures as a result of strenuous exercise - and heat exhaustion, which is not associated with organ damage. Heat exhaustion, the most common form of heat illness, makes it difficult for the body to regulate its temperature. Symptoms include general weakness, fatigue, dizziness, headache, muscle cramps, hyperventilation, nausea, and loss of muscle control. Heat stroke is the most serious form of heat illness, in which high body temperature causes central nervous system dysfunction and organ and tissue damage.
Investigators identified certain trends in soldiers over this period, including:
- Hospitalization rates for heat exhaustion have decreased approximately 60 percent. However, heat stroke hospitalizations increased by more than 500 percent.
- Heat stroke cases were associated with dehydration (17 percent) and acute kidney failure (13 percent), while 25 percent were related to rhabdomyolysis (muscle damage).
- Some groups of soldiers had lower rates of hospitalization overall, including African-Americans and Hispanic Americans (as compared to their Caucasian peers) and recruits from southern states. Women have a higher incidence of heat illness than men.
Overall, the total number of heat injuries has decreased significantly whereas the number of heat stroke cases has gradually increased since 1980. Most cases were due to activity from a scheduled training event, followed by exercises and other maneuvers. Also, during the last 20 years, running activities and dietary supplements have become more common in the military. The researchers also point out hydration awareness may cause some soldiers to continue exercising in the heat, which may lead to the development of a more serious heat injury.