Key takeaways:

• Officers face a higher risk for developing ALS than enlisted personnel.
• Longer time spent in service is associated with lower ALS risk.
• More research is needed into risk associations by job and base location.

The risk level of military service members developing ALS could be affected by which branch of the military they served in, with Air Force, Coast Guard and Navy veterans facing higher risks, according to data published in Neurology.

The research builds on a known association between military service and an increased risk for developing ALS, said Marc Weisskopf, PhD, ScD, professor of environmental epidemiology and physiology with the Harvard T.H. Chan School of Public Health.

Data derived from Roberts A, et al. Neurology. 2026:doi:10.1212/WNL.0000000000218303

“Part of the issue is that it’s been 20 or so years now where we’ve identified this rather notable increased risk of veterans to get ALS, but we’ve had a really hard time figuring out why,” Weisskopf told Healio.

Previous research has shown a connection between military service and ALS risk, but those studies generally examined a small number of cases, Weisskopf said.

A study that examined 226 cases from 2002 to 2015, published in 2019 in Military Medicine, found higher rates of ALS among Air Force veterans and lower rates among Marines.

The study also found higher rates of ALS among tactical operations officers when compared with administrators and general officers, including among pilots, aircraft crews and missile combat operations staff.

“There’s a lot that comes along with work on planes,” Weisskopf said. “For pilots and people in the planes, you get more radiation exposure if you’re up flying planes high in the sky, closer to solar radiation.”

Digging in

The current longitudinal cohort study by Weisskopf and colleagues included U.S. veterans who had an encounter with the VHA between Jan. 1, 2000, and Oct. 1, 2024.

The analytic sample comprised 9,157,938 men (mean age, 56.9 years) and 784,941 women (mean age, 42.4 years). There were 13,935 incident cases of ALS among the men and 484 incident cases among the women.

Among men, those in the Air Force had an ALS hazard ratio of 1.29 compared with men in the Army (95% CI, 1.23-1.35). For men in the Coast Guard and Navy, hazard ratios were 1.26 (95% CI, 1.06-1.5) and 1.15 (95% CI, 1.1-1.2), respectively.

The hazard ratio was lowest for men in the Marines, at 0.78 (95% CI, 0.68-0.88).

Although Weisskopf and colleagues used Army members for the reference group, Weisskopf emphasized that Army members are also at an increased risk for ALS compared with the general population.

Among women, service in multiple military branches was associated with a higher hazard ratio, while service in the Marines was associated with a lower hazard ratio, but neither association was significant, the authors wrote.

Officers had higher rates of ALS than enlisted personnel, with a hazard ratio of 1.64 for male officers (95% CI, 1.53-1.74) and 1.72 for female officers (95% CI, 1.31-2.27).

In general, longer service was associated with lower rates of ALS. The reasons for this warrant further research, Weisskopf said, but he offered several possibilities, including that the exposures that increase risk for ALS are more likely to be encountered in the early days of military experience.

The “healthy worker bias” could also be in play, Weisskopf said, referring to the possibility that the risk factors for ALS also cause other effects that lead service members to leave the service.

“What we are thinking is that some exposure in the Air Force maybe ultimately leads to ALS, but either as part of that process or just a separate one, leads to ill health or issues that make you less capable of continuing in the military,” Weisskopf said.

In age-stratified models, the difference in ALS hazard ratios relative to branch of service was more pronounced in the youngest age range. The hazard ratio for men aged 17 to 61 years ranged from 1.26 to 1.51, while the ratio for men aged 75 to 104 years ranged from 0.99 to 1.12.

The difference in hazard ratios between officers and enlisted personnel was also the lowest among the oldest age range. The hazard ratio for officers aged 17 to 61 years was 1.68 (95% CI, 1.44-1.96), compared with a ratio of 1.48 for officers aged 75 to 104 years (95% CI, 1.31-1.67).

Weisskopf said these findings suggest that the effects of military exposures on ALS may diminish over time.

Moving forward

Weisskopf said he views the study as one that “sets the stage” to dig deeper. Efforts to further explore the associations between military service and ALS risk would be bolstered by more detailed military history information at the individual level, including information on jobs, base locations and deployment locations, he said.

More details on jobs, for example, could help determine if pilots are at a greater risk to develop ALS than people fueling or cleaning the planes, Weisskopf said.

“What are the things going on in the Navy and the Air Force that maybe they get more exposure to than folks in the Army?” Weisskopf said. “That can then start to help us hone down on what the actual toxic bad actor is, and then that’s the point where you can potentially start to make some interventions.”

Previous research has also estimated the heritability of ALS to be between 40% and 80%, study authors wrote, citing data published in 2024 in the International Review of Neurobiology.

Weisskopf said he and his colleagues were interested in exploring the extent to which heritability is a factor in the ALS cases among military veterans. However, doing so would require obtaining genetic data for each case.

The data showing the differences in ALS risk by military branch made Weisskopf lean toward the idea that environmental exposures do play a role.

“It’s also probably likely that there’s some interplay here,” he said. “It may be that there is some genetic background on top of the exposures in the Air Force or the Navy, and that combination is what the problem is.”

In addition to the VA dataset used for the research, Weisskopf said another dataset exists within the U.S. Department of Defense with more information on jobs. However, because the data is separate from the VA’s health data, combining it has proven challenging, he said.

“We are desperately trying to combine those because that other data would tell us all sorts of information,” Weisskopf told Healio. “Each step is digging deeper and getting closer. Then we can come up with prevention and even think about how to slow the process.”

For more information:

Marc Weisskopf, PhD, ScD, can be reached at mweissko@hsph.harvard.edu.