Female military veterans who had traumatic brain injury (TBI), post-traumatic stress disorder (PTSD), or depression were more likely to develop dementia than female veterans without these conditions, researchers reported.
Having a TBI increased dementia risk in female veterans by 50%, while PTSD increased it by almost 80%, and depression increased it by almost 70%, according to Kristine Yaffe, MD, of the University of California San Francisco, and colleagues.
Moreover, women who had more than one of these military-related risk factors had more than a twofold risk of developing dementia, they wrote in Neurology.
“Our findings stress the need for both increased dementia screening in women with these risk factors and for more research on intervention strategies that might modify the effects of these risk factors,” said Yaffe.
“Almost nothing is known about dementia risk in female veterans, and this is the first study that we know of that has attempted to understand their dementia risk,” she told MedPage Today. “Although the risk factors that we focused on — TBI, PTSD, and depression — are not exclusive to military service, these risk factors are more prevalent in veterans, and PTSD and depression are also more prevalent in women.”
These risk factors are important to understand as more women take on combat roles, she added: nearly one in three veterans deployed for Operations Enduring Freedom and Iraqi Freedom are estimated to have one of these conditions.
It’s become increasingly apparent that military veterans are at higher risk than the general population for TBI, PTSD, and depression, observed Andrea Schneider, MD, PhD, and Geoffrey Ling, MD, PhD, both of Johns Hopkins University School of Medicine in Baltimore, in an accompanying editorial. “More women are joining the military, and there is increasing evidence of sex differences in dementia risk in the general population.”
Yaffe and colleagues studied the records of 109,140 female veterans ages ≥55 who received care at a Veterans Health Administration medical center from 2004 to 2015 with at least one follow-up visit. Their average age was 68.5; most women (74%) were non-Hispanic whites and 12% were non-Hispanic blacks.
The researchers determined diagnoses of TBI, PTSD, and depression from ICD-9-CM codes at inpatient and outpatient visits. In the sample, 81,135 women had none of these conditions; 20,410 had depression only, 1,363 had PTSD only, 488 had TBI only, and 5,044 had more than one condition.
During an average follow-up of 4.0 years, 4,125 female veterans (4%) developed dementia. After adjusting for demographics, socioeconomic status, and medical comorbid conditions, women with TBI, PTSD, and depression were more likely to develop dementia than women without these diagnoses:
- Women who had a TBI: adjusted sub-distribution hazard ratio (adjusted sHR) 1.49 (95% CI 1.01-2.20)
- Women with PTSD: adjusted sHR 1.78 (95% CI 1.34-2.36)
- Women with depression: adjusted sHR 1.67 (95% CI 1.55-1.80)
- Women with more than one diagnosis had the highest risk for dementia: adjusted sHR 2.15 (95% CI 1.84-2.51)
Links between TBI and dementia and between PTSD and dementia were similar to ones reported previously for male veterans, but the association between depression and dementia was lower for women than men.
This analysis highlights the need for further research, Schneider and Ling wrote: “Future studies will need to include both men and women to assess directly for possible interaction by sex in associations between TBI, PTSD, and depression and dementia risk.”
“Animal studies suggest sex differences in response to TBI and sex differences in the neurobiology of PTSD and depression,” they added. “Given this, it is possible that neuropsychiatric conditions may be differentially associated with dementia risk in men versus in women.”
Associations of TBI, PTSD, and depression with incident dementia weakened after accounting for the number of follow-up visits, the researchers noted. Women with one of those diagnoses had two to three times as many visits as women who did not have these diagnoses; this closer follow-up may have resulted in a dementia diagnosis earlier because providers had more opportunities to observe cognitive and functional changes.
The study has other limitations, they added. It relied solely on ICD-9-CM codes to define TBI, PTSD, depression, and dementia, not diagnostic interviews. It’s possible women with less severe symptoms of these disorders did not receive diagnoses and were not counted. The study is observational in nature, and no causal relationships can be determined, Yaffe added.
The study supported by the U.S. Department of Defense and the National Institute on Aging.
Yaﬀe disclosed relevant relationships with Takeda and Beeson Scientific.
Ling disclosed relevant relationships with the National Football League (NFL) Players Association and the NFL Health Foundation Board of Directors. Schneider disclosed no relevant relationships with industry.