Blast exposure and long-term diagnoses among veterans: a millennium cohort study investigation of high-level blast and low-level blast.

Background: The effects of blast overpressure (BOP) on brain health are increasingly recognized, yet longitudinal research into these effects after separation from military service remains limited. This study assessed the association between high-level blast (HLB) and low-level blast (LLB) exposure during military service using data from the Millennium Cohort Study (MCS) and diagnoses related to traumatic brain injury (TBI) diagnosed in the Veterans Health Administration (VHA). Method: MCS participants were included in the analytic sample if they responded to the 2013 survey, were separated from military service, and utilized VHA care for at least 2 years. HLB exposure was assessed using self-report of injury from a "blast/explosion/bullet" in the 2013 survey; LLB risk was determined using military occupational specialty as a proxy. Clinical diagnoses of five TBI severity levels (e.g., mild, penetrating), 22 TBI-related conditions (e.g., tinnitus, dementia/delirium, fatigue) and 10 mental health conditions (e.g., adjustment, bipolar, schizophrenia) were identified using ICD diagnosis codes. Modified Poisson regression with robust error variance was used to examine the relationships between HLB, LLB, and their interaction, adjusting for demographic and military characteristics for each diagnosis of interest. Results: Statistically significant associations were found between HLB and several TBI diagnoses, TBI-related conditions, and mental health conditions. LLB exposure was associated with only one TBI condition, eight TBI-related conditions, and two mental health conditions. In addition, significant interactions between HLB and LLB were observed for two TBI-related conditions and four mental health conditions. Conclusion: This study contributes to the growing body of evidence on the long-term effects of BOP on brain health. These findings may inform policy development and educational resources, provide metrics to calculate the potential financial burden on the VHA and increase understanding of long-term health outcomes associated with blast exposure. By utilizing a prospective design and examining VHA diagnoses, the research highlights the potential enduring effects of blast exposure that may continue to require healthcare services after military separation.