Medical and Psychiatric Risk Factors for Dementia in Veterans with and without Traumatic Brain Injury (TBI): A Nationwide Cohort Study

Background Traumatic brain injury (TBI) is a risk factor for dementia and is common, especially among Veterans. It is unknown whether TBI exposure moderates the effect of other common medical/psychiatric comorbidities that are also risk factors for dementia. If treatable or preventable risk factors have a different impact on TBI-exposed Veterans, then this may have important public health implications for dementia prevention. Objectives Determine prevalence of common medical/ psychiatric comorbidities and associated risk of dementia in Veterans with versus without TBI. Design Observational cohort. Setting Nationwide Veterans Health Administrative data 2001–2019. Participants After excluding baseline dementia, Veterans age ≥55 years with TBI (N=95,139) were age/sex/race-matched 1:2 with Veterans without TBI (N=190,278). Measurements We compared prevalence of hypertension, coronary artery disease (CAD), diabetes, cerebrovascular disease (CVD), epilepsy, depression, and post-traumatic stress disorder (PTSD) among Veterans with and without TBI. We calculated risk of incident dementia associated with each comorbidity using multivariable hazard ratios (HR) with Fine-Grey competing risk of death adjusted for baseline demographics. We estimated population attributable fraction (PAF) of dementia due to each comorbidity among Veterans with versus without TBI. Results Prevalence of all comorbidities were significantly more prevalent (5.7% to 21.5% higher) among Veterans compared to those without TBI. All comorbidities were associated with increased risk of dementia in both groups. There were significant interactions between comorbidities and TBI in which HRs were slightly lower among Veterans with TBI (adjusted HRs 1.08–1.37) compared to those without TBI (adjusted HRs 1.12–2.13). Nevertheless, PAFs for dementia due to depression, hypertension, CAD, CVD, and epilepsy were slightly higher in Veterans with TBI due to their high prevalence in this group. Conclusions Targeting depression, hypertension, CAD, CVD, and epilepsy may be especially important for dementia risk reduction among Veterans with TBI.