Veterans of the Air Force, Navy and Coast Guard may be at higher risk for developing amyotrophic lateral sclerosis (ALS) compared with veterans from other branches, according to research published in the journal Neurology.

In a review of 9.9 million veterans in the VA medical system from 2000 to 2024, researchers from the Harvard T.H. Chan School of Public Health, the Department of Veterans Affairs and elsewhere found that 14,419 patients had received an ALS diagnosis.

In the group with ALS, 46% were Army veterans – nearly the same percentage of soldiers in the entire patient cohort.

Using the rate of ALS diagnoses among Army veterans as the baseline and adjusting for sex, race, and ethnicity, researchers found that Air Force veterans had a 29% higher rate, former Coast Guard members had a 26% higher rate and Navy veterans had a 15% higher rate. Marines had the lowest rate, at 22% below that of Army veterans.

Overall, officers had a 64% higher rate than enlisted personnel, while women officers had a 72% higher rate. Differences among branches were more apparent in men ages 61 and younger and less evident among men older than 75.

“Our study looked at the rates of ALS among people in different branches of the U.S. military and found ALS rates varied considerably by branch and rank, with larger differences among younger veterans,” said study author Marc Weisskopf at the Harvard T.H. Chan School of Public Health in a release.

ALS is a rare disease diagnosed in roughly 5,000 Americans each year, according to the Centers for Disease Control and Prevention. A fatal illness most famously associated with baseball legend Lou Gehrig and British astrophysicist Stephen Hawking, it is a progressive disease that affects the motor neurons, causing them to lose connectivity and die off.

There are two types of ALS: sporadic, meaning occurring without a known cause in the general population, and familial, likely the result of an inherited genetic mutation, according to the ALS Association.

While military personnel are diagnosed with ALS at nearly twice the rate of civilians, the cause has not been scientifically proven. The VA presumes the condition to be service-connected given the heightened occurrence in the veteran population.

Researchers have theorized that exposure to hazardous environments and substances, including burn pits, jet fuel, exhaust, heavy metals, dioxins and other toxic materials, may contribute, but no direct connection has been proven.

“Our findings suggest that officers and those serving in the Air Force, Navy or Coast Guard may have been exposed to military environments that increase risk of ALS,” said Weisskopf. “Future research should aim to identify these exposures.”

In the civilian population, some occupations such as airline pilots, truck drivers, metal workers and those who work with pesticides and other toxic substances are associated with increased ALS risk, according to a 2022 Columbia University study.

The authors noted that the likelihood of developing ALS is low, even in the U.S. military. Of the 9.9 million veteran records reviewed, less than 0.2% of patients were diagnosed with ALS, according to the study.

“It is … important to note that ALS is rare and the overall risk remains small, so even statistically significant increases associated with branch and rank represent only modest increases in risk among military personnel,” Weisskopf said.