Risk of Cognitive Decline in Professional Soccer Players after Repetitive Subconcussive Impacts: A Systematic Review and Meta-analysis.

Abstract

Repetitive soccer heading has been implicated as a potential source of cumulative subconcussive brain injury, yet the magnitude and consistency of its cognitive effects remain incompletely defined. We conducted a systematic review and meta-analysis to quantify global and domain-specific cognitive outcomes associated with repetitive heading exposure. Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 guidelines, PubMed/MEDLINE, Scopus, and Web of Science were searched through December 2025. Of 2,846 identified records, 46 studies met the inclusion criteria, and 28 provided standardized cognitive data suitable for quantitative synthesis. Effect sizes (Hedges g, Fisher z) were transformed into log odds ratios and pooled using DerSimonian-Laird random-effects models. Heterogeneity was assessed using Q, I², and H² statistics, and publication bias was evaluated with funnel plots, Egger regression, and trim-and-fill procedures, alongside leave-one-out influence analyses. Across 28 independent author-level datasets, repetitive heading was associated with significantly increased odds of global cognitive underperformance (odds ratio 1.67; 95% confidence interval 1.61-1.72), with moderate heterogeneity (I² ≈ 34%). Trim-and-fill adjustment yielded a modestly attenuated but still significant estimate (odds ratio 1.49). Domain-level analyses demonstrated consistent impairments across visuospatial ability (odds ratio 1.49), verbal memory (odds ratio 1.62), attention (odds ratio 1.71), processing speed (odds ratio 1.64), executive function (odds ratio 1.86), and composite cognition (odds ratio 1.58). Confidence intervals were narrow, once, and the effect directionality was uniform across domains. These findings indicate that repetitive soccer heading is associated with robust, reproducible cognitive deficits across multiple cognitive systems, supporting cumulative subconcussive exposure as an independent risk factor for measurable cognitive decline.