A world-first study led by the University of Sydney has uncovered subtle but measurable changes in the brain following routine heading of a soccer ball — even in the absence of concussion or immediate cognitive symptoms.

Published in the journal Sports Medicine – Open, the randomized controlled trial used advanced Magnetic Resonance Imaging (MRI) to examine the brains of 15 adult male soccer players who headed a ball 20 times in 20 minutes under tightly controlled conditions. The results showed altered brain chemistry and decreased electrical conductivity in multiple brain regions — changes that may affect energy use and information transmission through white matter.

The study also found increased levels of two blood biomarkers — GFAP and NFL — which are considered reliable indicators of brain injury and have been linked to elevated dementia risk. Although the levels were well below those seen in diagnosed brain injury cases, researchers say the subtle elevations suggest a biological response to microstructural disruption in brain cells.