Over a single competitive season, male adolescent soccer players showed no statistically significant differences from noncontact-sport athletes in cognition, behavior, balance, or measures of brain structure and function, according to a prospective longitudinal cohort study published in JAMA Network Open. The study found higher preseason levels of two blood-based biomarkers studied in relation to brain injury, although these were not associated with reported heading exposure.
The study examined repetitive head impacts — repeated head contacts that do not cause clinical concussion — using magnetic resonance imaging, neurocognitive and behavioral testing, balance assessment, magnetic resonance spectroscopy, and plasma biomarkers across one season. Because soccer is the most widely played sport among youth worldwide, the researchers set out to determine whether participation was associated with measurable short-term changes in the developing brain.
Why It Matters for Physicians
Heading restrictions and other precautionary policies in youth soccer have advanced in some countries despite limited prospective evidence in adolescents, the researchers noted, and prior work in this area has been largely small, cross-sectional, and heterogeneous. The findings provide short-term prospective data that physicians may use when discussing youth soccer participation with athletes and families, while recognizing that the study does not address long-term risk.
Key Findings
Researchers enrolled 129 male athletes aged approximately 15 years across centers in Germany, Belgium, and Norway, including 82 soccer players and 47 noncontact-sport athletes. Soccer players reported a mean of 939 headers during the season. Heading exposure varied substantially among players. Assessments were performed at preseason, postseason, and 2 months following the season.
The prespecified primary analysis compared between-group differences in change over time. Across the season, soccer players did not differ statistically from controls in cognition, behavior, balance, cortical thickness, brain volumes, white-matter microstructure, or resting-state functional connectivity. Within soccer players, heading exposure was not associated with changes in any measured outcome.
At preseason, soccer players had higher levels of total N-acetylaspartate, plasma neurofilament light chain, and glial fibrillary acidic protein than controls. Total N-acetylaspartate levels converged between groups by postseason, whereas GFAP and NfL trajectories did not differ significantly between groups over time. Heading exposure was not associated with these findings.
What This Does Not Show
This was an observational, nonrandomized study, so the findings describe associations rather than effects, and residual confounding cannot be excluded. The absence of statistically significant differences should be read as no detected difference within the sensitivity limits of this sample rather than as evidence of no effect; the researchers noted that no formal power calculation was performed and that the study may have been underpowered to detect small effects. A single competitive season cannot address long-term or cumulative outcomes, which may require years of exposure to manifest. Heading exposure was self-reported and is best interpreted as a relative rather than absolute measure, a limitation the researchers said could bias exposure–outcome associations toward the null.
Clinical Context
For physicians counseling adolescent soccer players and their families, the study found no statistically significant between-group differences over one season in cognitive, behavioral, balance, structural imaging, diffusion imaging, or functional connectivity outcomes. However, preseason differences were observed in total N-acetylaspartate, GFAP, and NfL, and the authors cautioned that these findings require further study.
The findings do not address long-term or cumulative effects of repetitive head impacts. The researchers concluded that risk-mitigation approaches — including age-appropriate heading guidance and education — together with large, multiyear studies remain essential to inform child health policy. They also noted that the findings reflect changes measured during one additional season in athletes who already had several years of prior soccer experience.
Disclosures: The study was led by Inga K. Koerte, MD, of Ludwig Maximilians University Munich, and colleagues. The study was funded through the ERA-NET Neuron framework and national funding agencies. Dr. Koerte and several co-investigators reported research funding, consulting relationships, or other disclosures; full disclosures are available in the study.
Source: JAMA Network Open
