# Annual level changes of serum neuronal and glial biomarkers in a German professional football club

## TL;DR

This study tracks changes in brain injury biomarkers in professional football players over two years to assess potential risks from repeated head impacts.

## Contribution

The study provides empirical evidence that serum NfL and GFAP levels can monitor brain health in football players without significant association to headers or physical activity.

## Key findings

- Serum NfL and GFAP concentrations in PFPs showed significant changes over time (p < 0.001).
- Biomarker levels increased after mild TBI but returned to normal within days.
- No significant association was found between biomarkers and physical activity or headers.

## Abstract

Professional football players (PFP) experience repeated mild traumatic brain injuries (TBI) and have an increased long-term dementia risk. We aimed to assess annual level changes of blood neuronal (neurofilament light chain, NfL) and astroglial (glial fibrillary acidic protein, GFAP) biomarkers in PFPs over 2 years.

We measured with commercial immunoassays NfL and GFAP concentrations n = 129 serum samples obtained from n = 43 male PFPs playing for a German professional football team. Samples were collected at five time points over 2 years and before/after an index match. Associations between blood markers and potential sources of neuronal damage, such as intense physical activity, injuries, and headers, were tested.

Serum NfL and GFAP concentrations in PFPs were significantly different at repeated measurements (p < 0.001) but were not associated with metrics of physical activity, total time of physical activity, total number of headers, and headers-per-match. After injuries with mild TBI, serum NfL and GFAP increased and returned to normal levels within few days. Before and after an index match, serum levels of NfL and GFAP were not significantly different, nor they were significantly associated with physical activity and headers.

Serum NfL and GFAP may be used to monitor PFP over time. Repeated headers and intense physical activity in PFPs seem to be safe on a neurochemical level.

The online version contains supplementary material available at 10.1007/s00415-025-13176-z.