Association of life‐course traumatic brain injury with dementia risk: A nationwide twin study

INTRODUCTION: The impact of life‐course traumatic brain injury (TBI) on dementia is unclear. METHODS: Within the Swedish Twin Registry (STR), 35,312 dementia‐free twins were followed for up to 18 years. TBI history was identified via medical records. Data were analyzed using generalized estimating equation (GEE) and conditional logistic regression. RESULTS: In multi‐adjusted GEE models, the odds ratio (OR, 95% confidence interval [CI]) of dementia was 1.27 (1.03–1.57) for TBI at any age, 1.55 (1.04–2.31) for TBI at 50 to 59 years, and 1.67 (1.12–2.49) for TBI at 60 to 69 years. Cardiometabolic diseases (CMDs) increased dementia risk associated with TBI at age 50 to 69 years. The ORs in GEE and conditional logistic regression did not differ significantly (P = .37). DISCUSSION: TBI, especially between ages 50 and 69 years, is associated with an increased risk of dementia, and this is exacerbated among people with CMDs. Genetic and early‐life environmental factors may not account for the TBI–dementia association.