Dementia and Alzheimer’s disease in former contact sports participants: population-based cohort study, systematic review, and meta-analysis

Abstract

SummaryImportanceThere is uncertainty regarding the long-term risk of dementia in individuals with a history of participation in sports characterised by repetitive head impact, and whether the occurrence of this disease differs between former amateur and professional athletes.ObjectiveTo quantify the dementia risk in former athletes with a background in contact sports using new cohort study data incorporated into a meta-analysis.Data sources and study selectionThe cohort study comprised 2005 male retired athletes who had competed internationally for Finland (1920-1965) and a general population comparison group (N=1386). For the systematic review, we searched PubMed and Embase from their inception to August 23 2022, including cohort studies published in English that reported standard estimates of association and variance.Data extraction and synthesisStudies were screened and results extracted independently by two authors. Study-specific estimates were aggregated using random-effect meta-analysis. An adapted Cochrane Risk of Bias Tool was used to assess study quality.Main outcomes and measuresThe primary outcomes were dementia and Alzheimer’s disease.ResultsThe systematic review identified 827 potentially eligible published articles, of which 7 met the inclusion criteria. Incorporating the new results from the Finnish cohort study with those from the systematic review revealed that former boxers had higher rates of dementia (2 studies: summary risk ratio 3.14 [95% CI 1.72, 5.74], I2=34%) and Alzheimer’s disease (2 studies: 3.07 [1.01, 9.38], I2=55%), as did retired soccer players (3 studies of dementia: 2.78 [1.69, 4.59], I2=86%; 2 studies of Alzheimer’s disease: 3.22 [1.34, 7.75], I2=81%). While the pooled estimate for dementia in retired American football players was less convincing (4 studies: 1.63 [0.76, 3.49], I2=75%), disease occurrence in onetime professionals was markedly higher (2.96 [1.66, 5.30]) than amateurs in whom there was no association (0.90 [0.52, 1.56]). There was also a risk differential for retired professional (3.61 [2.92, 4.45]) and amateur (1.60 [1.11, 2.30]) soccer players.Conclusion and relevanceBased on studies exclusively comprising men, former participants in contact sports subsequently experienced poorer brain health, and there was a suggestion that retired professionals had the greatest risk.Key pointsQuestionDo former participants in contact sports have a greater risk of dementia than the general population?FindingsCompared with general population controls, retired male participants from the contact sports of boxing, soccer, and American football appeared to have an elevated risk of dementia at follow-up. For soccer and American football, the risk in former professionals was higher than erstwhile amateurs.MeaningRetired male contact sports participants seem to subsequently experience poorer brain health.