Background: The ε4 allele of apolipoprotein E (APOE) and head injury are risk factors for dementia diseases, and may act synergistically to further increase the risk. The aim of this study was to examine the association between mild head injury, APOE and dementia.
Methods: Data were obtained from the Betula prospective population-based study of aging, memory, and health. The study included 543 participants in the age range 40–85 years, free of dementia at baseline, who were followed up within a 5-year interval. Dementia was classified using DSM-IV criteria. Information on previous head injury was obtained through screening of the participants' answers to health questionnaires at baseline and at follow-up.
Results: Subjects with head injury but without APOE ε4 had no increased risk of dementia. Subjects with APOE ε4 had an increased risk and those with both APOE ε4 and head injury had the highest risk of dementia (odds ratio = 5.2).
Conclusions: APOE ε4 constitutes a risk factor for dementia, mild injury in isolation does not increase the risk, but head injury in combination with the APOE ε4 leads to increased risk of dementia.