Traumatic brain injury and cognitive change over 30 years among community‐dwelling older adults

INTRODUCTION There is limited evidence regarding the rate of long‐term cognitive decline after traumatic brain injury (TBI) among older adults. METHODS In this prospective cohort study, time‐varying TBI was defined by self‐report and International Classification of Disease diagnostic codes. Cognitive testing was performed at five visits over 30 years and scores were combined into a global cognition factor score. Adjusted linear mixed‐effects models estimated the association of TBI with cognitive change. RESULTS A total of 11,701 Atherosclerosis Risk in Communities (ARIC) Study participants (mean baseline age 58 years, 58% female, 25% Black) without TBI at baseline were included. Over follow‐up, 18% experienced TBI. The adjusted average decline in cognition per decade (standard deviation units) was more than twice as fast among individuals with ≥ 2 incident TBIs (β = –0.158, 95% confidence interval [CI] = –0.253,–0.063), but not among individuals with 1 TBI (β = –0.052, 95% CI = –0.107, 0.002), compared to without TBI (β = –0.057, 95% CI = –0.095, –0.020). DISCUSSION This study provides robust evidence that TBIs fundamentally alter the trajectories of cognitive decline. Highlights The adjusted average decline in cognition per decade (standard deviation units) was more than twice as fast among individuals with ≥ 2 incident traumatic brain injuries (TBIs; β = –0.158, 95% confidence interval [CI] = –0.253, –0.063), but not with 1 TBI (β = –0.052, 95% CI = –0.107, 0.002), compared to without TBI (β = –0.057, 95% CI = –0.095, –0.020). Over a period of 30 years, this difference in cognitive decline is equivalent to individuals with ≥ 2 TBIs being 9.7 years older at baseline. Associations of TBI were stronger among individuals with one or two apolipoprotein E (APOE) ε4 alleles than among individuals with zero APOE ε4 alleles (P interaction = 0.007).