JAMA Netw Open. 2026 Jun 1;9(6):e2619569. doi: 10.1001/jamanetworkopen.2026.19569.
ABSTRACT
IMPORTANCE: Repetitive head impacts (RHIs) are associated with later-life neurodegeneration. Because soccer is the most widely played sport among youth worldwide, identifying early changes associated with RHI is important.
OBJECTIVE: To determine whether participation in 1 season of youth soccer is associated with changes in cognition, behavior, balance, brain structure or function, or blood biomarkers compared with noncontact sports.
DESIGN, SETTING, AND PARTICIPANTS: Prospective longitudinal cohort study at European centers (Munich, Germany; Leuven, Belgium; and Oslo, Norway). Male adolescent soccer players and noncontact athletes were each studied across a single competitive season with assessments at preseason, postseason, and 2 months later. Data were analyzed from January 2023 to March 2025.
EXPOSURES: Soccer players were compared with noncontact athletes. In addition, self-reported heading of a soccer ball was assessed among soccer players as a measure of RHI.
MAIN OUTCOMES AND MEASURES: Cognition, behavior, balance, magnetic resonance imaging (brain structure, function, and biochemistry), and plasma biomarkers.
RESULTS: Male adolescent soccer players (n = 82; mean [SD] age, 14.8 [0.6] years) did not differ from noncontact sport athletes (n = 47; mean [SD] age, 14.7 [0.7] years) in cognition, behavior, balance, cortical thickness, brain volumes, white-matter microstructure, or functional connectivity. At preseason, soccer players had higher total N-acetylaspartate (tNAA; β, -0.379 [95% CI, -0.627 to -0.131]; P = .003), glial fibrillary acidic protein (GFAP; β, -0.055 [95% CI, -0.103 to -0.006]; P = .03), and neurofilament light chain (NfL; β, -0.071 [95% CI, -0.122 to -0.020]; P = .01) than noncontact sport controls. Across the season, tNAA (β, 0.047 [95% CI, 0.020-0.074]; P = .001) declined in soccer players and increased in controls, converging by postseason. Group trajectories of GFAP and NfL did not differ between groups. Within soccer players, heading exposure was not significantly associated with changes in any outcome.
CONCLUSIONS AND RELEVANCE: In this cohort study of adolescent males, no statistically significant differences were detected over 1 season between soccer players and noncontact sport athletes in cognition, behavior, or brain structure and function. Group differences in GFAP and NfL may represent early signs of exposure, but lack of association with heading exposure warrants further investigation. These results highlight the need for large, multiyear studies to inform health policy.
PMID:42329650 | DOI:10.1001/jamanetworkopen.2026.19569
