Highlights
- Traumatic Brain Injury (TBI) and depression were found to nearly triple the 10-year hazard of incident Alzheimer Disease and Related Dementias (ADRD).
- Alcohol Use Disorder (AUD) remains a potent modifiable risk factor, doubling the risk of dementia in the aging Veteran cohort.
- Military-specific environmental exposures, including Agent Orange and pyridostigmine bromide tablets, are significantly associated with increased ADRD incidence.
- Findings from the Million Veteran Program (MVP) provide a high-resolution map for targeted screening and early intervention in high-risk Veteran populations.
Background: The Growing Burden of Dementia in the Veteran Population
Alzheimer disease and related dementias (ADRD) represent one of the most significant public health challenges facing the United States, particularly within the Veterans Health Administration (VHA). Currently, approximately 450,000 Veterans are living with ADRD, a number expected to rise as the Veteran population continues to age. While age and the APOE-ε4 allele are non-modifiable cornerstones of dementia risk, there is an urgent clinical need to identify modifiable individual-level factors that can be targeted to delay or prevent cognitive decline.
Veterans often possess a unique profile of risk factors compared to the general population. Military service involves exposure to physical trauma, chronic psychological stress, and various environmental toxins. Understanding how these service-related factors interact with lifestyle and comorbid health conditions is essential for developing precision medicine approaches to brain health. This study, utilizing the robust dataset of the Million Veteran Program (MVP), aimed to quantify these risks over a decade of observation.
Study Design: Leveraging the Million Veteran Program (MVP)
This retrospective cohort study utilized data from the Million Veteran Program, one of the world’s largest databases of health and genomic information. The researchers included 245,949 Veterans who were aged 65 years or older at the time of their MVP enrollment. All participants had completed the MVP Baseline Survey and had comprehensive electronic health record (EHR) data available through the VA system.
The study characterized a broad spectrum of variables, categorized into sociodemographic factors, health behaviors (e.g., smoking, alcohol use), health conditions (e.g., TBI, depression, cardiovascular disease), and military environmental exposures (MEEs). The MEEs specifically examined included Agent Orange, chemical or biological warfare agents, and pyridostigmine bromide (PB) tablets—the latter often used as a prophylactic against nerve agents during the Gulf War.
The primary outcome was the 10-year incidence of ADRD, identified via a validated algorithm using International Classification of Diseases (ICD) codes. Statistical analysis employed separate Cox regression models for each risk factor, adjusting for potential confounders such as age, sex, and educational attainment, to determine the Hazard Ratio (HR) and 95% Confidence Intervals (CI).
Key Findings: Identifying the Drivers of ADRD Risk
The study population was predominantly male (97.41%) with a mean age of 73.16 years. Over the 10-year follow-up period, 11,216 Veterans (4.56% of the sample) developed ADRD. The results highlighted several critical health conditions and exposures that significantly shifted the risk trajectory.
The Impact of Health Conditions and Behaviors
The strongest associations with incident ADRD were found in neuropsychiatric and traumatic conditions. Veterans with a history of Traumatic Brain Injury (TBI) faced a nearly threefold increase in risk (HR 2.96, 95% CI 2.76-3.17). Similarly, depression was a massive driver of incidence (HR 2.93, 95% CI 2.82-3.04). Alcohol Use Disorder (AUD) also emerged as a primary modifiable risk factor, more than doubling the hazard of dementia (HR 2.35, 95% CI 2.19-2.53).
These findings underscore that the “invisible wounds” of war—mental health struggles and head trauma—have long-term consequences that manifest as neurodegenerative disease decades later. The magnitude of these hazard ratios suggests that managing depression and AUD, and monitoring those with TBI, should be prioritized in geriatric VA care.
The Role of Military Environmental Exposures (MEEs)
A unique aspect of this study was the evaluation of MEEs, which are often difficult to track in non-military cohorts. The data revealed that Veterans exposed to Agent Orange had a significantly higher risk of ADRD (HR 1.09, 95% CI 1.03-1.14). More striking were the associations with chemical/biological warfare agents (HR 1.31, 95% CI 1.23-1.39) and pyridostigmine bromide (PB) tablets (HR 1.67, 95% CI 1.44-1.93).
The elevated risk associated with PB tablets is particularly noteworthy for Gulf War-era Veterans. These tablets, designed to protect against soman nerve gas, have long been a subject of investigation regarding Gulf War Illness, but their specific link to long-term ADRD incidence in this large cohort adds a new dimension to our understanding of veteran-specific neurotoxicity.
Expert Commentary: Mechanistic Insights and Clinical Implications
The findings from Clark et al. provide a sobering look at the long-term cognitive costs of military service and associated health conditions. From a mechanistic perspective, the strong link between TBI and ADRD is well-supported by literature suggesting that axonal injury and chronic neuroinflammation can trigger the deposition of beta-amyloid and tau proteins. However, the HR of 2.96 observed here is particularly high, potentially reflecting the severity or frequency of injuries sustained by this cohort.
The association with depression raises the perennial question of whether depression is a causative risk factor or a prodromal symptom of dementia. Given the 10-year follow-up, it is likely that chronic, mid-life depression contributes to a reduction in cognitive reserve or exacerbates vascular pathologies that lead to ADRD. In the VA system, where depression prevalence is high, aggressive treatment of late-life mood disorders may serve as a vital neuroprotective strategy.
The environmental exposure data also warrants attention. The neurotoxic effects of organophosphates (related to PB tablets) and herbicides (Agent Orange) may involve oxidative stress and mitochondrial dysfunction. Clinicians should ensure that exposure histories are thoroughly documented, as these factors may help identify Veterans who require more frequent cognitive screening.
Study Limitations
While the MVP dataset is expansive, the study has limitations. The sample was overwhelmingly male (97.4%), which limits the generalizability of the findings to female Veterans. Furthermore, the use of ICD codes for ADRD diagnosis, while validated, may miss early-stage cognitive impairment or misclassify specific dementia subtypes (e.g., distinguishing between Alzheimer’s and vascular dementia). Finally, the observational nature of the study means that while associations are strong, causality cannot be definitively proven.
Conclusion: A Roadmap for Precision Prevention
This study identifies TBI, depression, and AUD as the primary individual-level factors associated with a 10-year incidence of ADRD in Veterans. By highlighting the additional risk posed by military environmental exposures, the research provides a more comprehensive picture of the unique vulnerabilities of those who have served. For the VHA, these results suggest that the most effective way to combat the rising tide of dementia is to focus on the holistic management of mental health, substance use, and the long-term monitoring of those with a history of service-related trauma or toxic exposure.
References
1. Clark AL, Asimakopoulos G, Valocchi E, et al. Individual-Level Factors Associated With 10-Year Incidence of Alzheimer Disease and Related Dementias in the VA Million Veteran Program. Neurology. 2026;106(7):e214748. PMID: 41805402.
2. Gilsanz P, et al. Female Veterans and Dementia Risk: Gaps in Current Literature. Journal of Geriatric Psychiatry. 2023.
3. VA Million Veteran Program (MVP). Research Highlights and Data Access. 2024.
