Documented head injury in early adulthood and risk of Alzheimer's disease and other dementias

Background: The association between antecedent head injury and AD is incons istent. Objective: To examine the association between early adult head inju ry, as documented by military hospital records, and dementia in late life; and to evaluate the interaction between head injury and APOE epsilon4 as ri sk factors for dementia. Methods: The study had a population-based prospect ive historical cohort design. It included men who were World War II Navy an d Marine veterans, and were hospitalized during their military service with a diagnosis of either a nonpenetrating head injury or another unrelated co ndition. In 1996 to 1997, military medical records were abstracted to docum ent; the occurrence and details of closed head injury. The entire sample wa s then evaluated for dementia and AD using a multistage procedure. There we re 548 veterans with head injury and 1228 without head injury who completed all assigned stages of the study. The authors estimated risk of dementia, specifically AD, using proportional hazards models. Results: Both moderate head injury (hazard ratio [HR] = 2.32; CI = 1.04 to 5.17) and severe head i njury (HR = 4.51; CI = 1.77 to 11.47) were associated with increased risk o f AD. Results mere similar for dementia in general. The results for mild he ad injury were inconclusive. When the authors stratified by the number of A POE epsilon4 alleles, they observed a nonsignificant trend toward a stronge r association between AD and head injury in men with more epsilon4 alleles. Conclusions: Moderate and severe head injuries in young men may be associa ted with increased risk of AD and other dementias in late life. However, th e authors cannot exclude the possibility that other unmeasured factors may be influencing this association.