Dementia risk factors in former contact sports participants: prospective cohort study.

Background: The elevated dementia incidence in retired contact sport participants might be explained by a higher prevalence of established risk factors for the disease relative to the general population. Methods: In this cohort study, former elite participants active between 1920 and 1965 in soccer (N=303), boxing (N=281), and wrestling (N=318) were recruited using sports yearbooks and records of sports associations. Men in a population control group were identified using records from a compulsory medical examination (N=1712). All study members were linked to hospital registers (1970-2015) and self-completion questionnaires were circulated (1985, 1995) from which we captured data on nine established risk factors for dementia: hypertension and diabetes status, alcohol intake, loneliness, depressive symptoms, cigarette smoking, body weight, educational attainment, and physical activity. Results: There was little suggestion that former participants in contact sports had a higher prevalence of dementia risk factors relative to the general population. Rather, the balance of evidence was for more favourable risk factor levels in former athletes, as was particularly evident for ever having smoked cigarettes (range in odds ratios [95% confidence interval]: 0.32 [0.21, 0.48] for wrestling to 0.52 [0.36, 0.75] for soccer) and leisure-time physical activity (range in beta coefficients [95% confidence interval]: 1.34 [0.66, 2.02] for soccer to 1.80 [1.07, 2.52] for boxing). Conclusions: The increased dementia rates in retired contact sport participants evident in epidemiological studies is unlikely to be explained by the risk factors examined here. This implicates other characteristics of contact sports, including a history of repeated head impact.