For the past 20 years — and longer before that — service members have come back from deployment talking about mental health issues and illnesses they say were linked to their time in the military, many of their concerns. being supported by various studies.
Now, a study that has been following military personnel, active duty and veterans, for 20 years supports the theory that combat experience can have adverse physical and health effects.
Researchers from the Naval Health Research Center and Veterans Affairs Puget Sound have studied service members of all branches for the past 20 years, using surveys to determine the effects time in the military might have on mental health. and physics as part of the Millennium Cohort study.
Researchers working on the study have written about their work since the start, but recently published a review of the literature in the journal Annals of Epidemiologymeaning the authors analyzed previously published material to identify broader trends over the years.
Although the study, which is sponsored by the Department of Defense, included 260,000 military personnel from all branches, it did not break down the results by branch. The military had the most participants, accounting for 40% of enrollees, said Rudy Rull, senior epidemiologist at the Naval Health Research Center.
Of the enrollees, two-thirds were active duty and the remaining third were reserve or National Guard. Of those surveyed, 60% are no longer in the military, Rull said.
The Millennium Cohort study is a prospective study, which has continued to recruit participants over the years. It was originally scheduled to end in 2022, but the study has been extended to 2068, with the most recent participants enrolled between September 2020 and August 2021.
The most recent enrollment period resulted in an additional 50,000 participants, including some from Space Force.
One of the reasons for the study is that members of the military community have noticed health problems in service members and veterans, but it was difficult to examine the causes through retrospective studies, said Dr. Margaret Ryan, Regional Medical Director of Defense Health. Agency Vaccination Office. Ryan was one of the people involved in the early days of the study.
The cohort study arose out of the need for prospective studies, Ryan said, adding that it was based on other studies, such as the Nurses’ Health Studies I and II, which look at women’s health.
“And the Millennium Cohort was designed in that vein, by a senior epidemiologist who said, ‘If we had this cohort study, we could answer so many questions so much better than ever before,'” Ryan said.
One of the most consistent findings from the literature review was that combat increases the likelihood of suffering from mental health problems, with post-traumatic stress disorder being the most common outcome. Service members who fought while deployed were three times more likely to report PTSD symptoms or a diagnosis compared to those who did not deploy. Depression was also higher among those who witnessed combat while deployed.
The risk of post-deployment PTSD was also higher for those who had been physically or sexually assaulted before deployment, had poor baseline mental health, had been seriously injured in combat, or had been deployed multiple times, the study found.
At the same time, there were many who had not suffered from PTSD. Of the sampled service members who were deployed and did not fight, 90% had low levels of PTSD symptoms. Of those who saw combat while deployed, 80% had low levels of PTSD.
The study also reviewed suicide research done with the Millennium Cohort and found that there was no direct relationship between deployment and suicide risk. Instead, he found that the risk factors were being male, having bipolar disorder or depression, or having problems with alcohol use. Another study reviewed by the literature review found that combat violence or particular incidents, such as the killing of a civilian, were associated with suicide attempts, although mental disorder was a confounder.
Overall, along with physical health, deployment was not necessarily harmful, although specific deployment-related exposures were associated with poorer health. The literature review focused on respiratory health, autoimmune diseases, and cardiometabolic health, but did not focus on cancers.
In particular, the study looked at the effects of combustion fireplaces on autoimmune and respiratory diseases, according to the study. A recent episode of “The Trouble with Jon Stewart” looked at burning fireplaces, which some veterans have linked to a range of health problems, including cancers. President Joe Biden also raised concerns about hotspots during his State of the Union Address Tuesday, claiming they may have affected her son, Beau, who died of brain cancer in 2015.
The study is survey-based, which means it comes with inevitable survey bias, which is when people answer surveys based on what they think investigators want to see. To combat this bias, the researchers also used Department of Defense medical records to compare surveys, Rull said.
The partnership with the Department of Veterans Affairs also gave researchers access to these files, Rull said.
When it comes to inconsistencies between medical records and investigations, researchers have generally found that a person wouldn’t deny they had a disease, said one of the founding investigators, Dr. VA Puget Sound staff.
However, people would say they had unlisted conditions on file, Boyko said. That didn’t mean they didn’t have the condition, just that the records might not reflect it.
Other limitations include recall and selection, Ryan said.
And, because this is a longitudinal study, it’s difficult to keep participants engaged, Rull noted.
As the researchers will continue the study for more than 40 years, they said there are more discoveries to come.
One finding will likely be the effect of COVID-19 on service members, as the last panel signed up before the pandemic began.
Interestingly, the first and last enrollment periods happened during life-changing events, Ryan said.
“We had this… global event that happened on 9/11,  just as we were in the process of enrolling this first panel into the cohort,” she said. And… it changed things a bit, just like the pandemic did. And yet, the study team itself is resilient and understands this.