Exertional heat injuries pose annual threat to U.S. service members

Summer is in full swing as the temperatures rise and the warm weather triggers heat illnesses that could threaten the readiness of the U.S. Armed Forces – especially among the youngest and most inexperienced service members and those training at installations in the southeastern United States.

“Prevention and treatment of heat illness among service members is important to the U.S. military because it speaks to readiness. Heat illnesses put warfighters at risk, making them unable to complete tactical missions. Moreover, trends are not decreasing,” said Dr. Francis G. O’ Connor, a professor and chair of Military and Emergency Medicine and associate director for the Consortium on Health and Military Performance at the Uniformed Services University of the Health Sciences.

In 2016, the number of cases of heat stroke among active component service members was 401, declining 4.1 percent from 418 cases in 2015. But the annual number of cases of “other heat illness” – known as heat exhaustion and “unspecified effects of heat” – was 2,135 in 2016, up 6.7 percent from 2,001 cases in 2015, according to recent analysis published in the peer-reviewed journal the Medical Surveillance Monthly Report (MSMR). The term “heat illness” refers to a spectrum of disorders that occur when the body is unable to dissipate heat absorbed from the external environment and the heat generated by internal metabolic processes.

In 2016, the overall incidence rates of heat stroke and “other heat illness” were 0.31 and 1.65 cases per 1,000 person-years (p-yrs.), respectively. Incidence rates of heat stroke were highest among males and service members aged 19 years or younger, Asian/Pacific Islanders, Marine Corps and Army members, recruit trainees, and those in combat-specific occupations. The incidence rate of heat stroke among female service members was 44 percent lower than the rate among males.

In contrast, the incidence rate of “other heat illnesses” was higher among females than males. Rates were also higher among service members aged 19 years or younger, Marine Corps and Army members, recruit trainees, and service members in combat-specific occupations, according to the analysis in the MSMR.

“The main causes of heat illness are not being adequately acclimatized to heat and humidity in a local environment, lack of adequate fitness for the demands of the task, and the competitiveness of the training environment,” Dr. O’Connor said. “Baseline fitness is very important to protect against heat illness. An increasing number of recruits may face challenges that they have not seen before, as the nation currently struggles with issues of decreasing fitness levels and increasing problems with overweight and obesity. This is why good military leadership is key— because good leaders help encourage proper training, education, and preparation for the warm weather by showing their people how to protect themselves in the heat while recognizing heat can hurt them.”

Military leadership can minimize heat illnesses and injuries among recruits and service members by knowing prevention guidelines, knowing service members’ physical limits, and promoting the buddy system. 

“Protecting recruits and service members from heat exhaustion is to encourage starting workouts at a lower intensity, be well hydrated and familiar with onsite hydration and cooling sources,” said Dr. O’Connor who has been a leader in sports medicine and education and research for the military for more than 20 years. “The most common time of the day for heat strokes to happen is the morning hours or during a series of hot days.” He said it is safer to schedule intense workouts during the cooler parts of day.

Dr. O’Connor also warns service members about the potential hazards of using pre-workout supplements. These supplements often contain dangerous additives such as amphetamines that have been linked to side effects, including heat intolerance, increased risk of heat stroke or seizures, high blood pressure, heart failure, and even sudden cardiac death.

“It’s important to use pre-workout supplements with caution and understand how they could affect your body, ideally discussing them with a knowledgeable health care provider, “he said. “But they should not be used in the heat.”

The MSMR full report of the heat illness annual update, including updates on exertional rhabdomyolysis and exertional hyponatremia, can be accessed in the March 2017 – Volume 24/3 issue.

About the Medical Surveillance Monthly Report (MSMR)

The MSMR is a peer-reviewed journal and AFHSB's flagship publication, provides evidence-based estimates of the incidence, distribution, impact, and trends of health-related conditions among service members. Additionally, the MSMR focuses one issue per year on the absolute and relative morbidity burden attributable to various illnesses and injuries among service members and beneficiaries. To stay informed about the health-related conditions that affect service members, subscribe to the MSMR to receive a monthly email alert of each issue.