Head injury and dementia: A co-twin control study of Swedish twins

History of head injury was examined as a risk factor for dementia and Alzheimer's disease using 167 same-sex twin pairs discordant for dementia in a co-twin control design. In addition to head injury with loss of consciousness, this study examined milder head injury, participation in contact sports, workplace use of vibrating equipment, and APOE-e4, a genetic risk factor. APOE-e4 did appear to be a risk factor for Alzheimer's disease, as expected. None of the other factors examined were associated with a significant increase in the risk of Alzheimer's disease or dementia. The relative risk for head injury with loss of consciousness was 1.2 (95 % CI 0.5--2.8) for dementia and 1.0 (95% CI 0.3--3.4) for Alzheimer's. History of playing contact sports was found to have a significant inverse relationship to dementia for males. Results indicate that an association between head injury and Alzheimer's disease is not found when cases and controls are well-matched.