Protocol for an Observational Study on the Effects of Early-Life Participation in Contact Sports on Later-Life Cognition in a Sample of Monozygotic and Dizygotic Swedish Twins
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A large body of work links traumatic brain injury (TBI) in adulthood to the onset of Alzheimer's disease (AD). AD is the chief cause of dementia, leading to reduced cognitive capacity and autonomy and increased mortality risk. More recently, researchers have sought to investigate whether TBI experienced in early-life may influence trajectories of cognitive dysfunction in adulthood. It has been speculated that early-life participation in contact sports---a leading cause of concussions among adolescents---may lead to poor cognitive and mental health outcomes. However, to date, the few studies to investigate this relationship have produced mixed results. We propose to extend this literature by conducting a study on the effects of early-life participation in contact sports on later-life cognitive health using the prospective Swedish Adoption/Twin Study on Aging (SATSA). The SATSA is unique in its sampling of monozygotic and dizygotic twins reared together (respectively MZT, DZT) and twins reared apart (respectively MZA, DZA). The proposed analysis is a study of 674 individuals (40 MZA, 98 DZA, 68 MZT, and 80 DZT, 102 unpaired singletons). 595 individuals in the analytic sample did not participate in contact sports and 79 did. 236 twin pairs were concordant for no participation in contact sports; 21 twin pairs were concordant for participation in contact sports; and 29 twin pairs were discordant for participation in contact sports. Our primary outcome will be a measure of global cognition assessed through the Mini-Mental State Examination (MMSE). We will also consider several secondary cognitive outcomes including verbal and spatial ability, memory, and processing speed. Our sample will be restricted to individuals with at least one MMSE score out of seven repeated assessments spaced approximately three years apart. We will adjust for age and sex in each of our models.
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