A new study published in
JAMA Neurology reveals that a single header is enough to temporarily increase blood levels of proteins associated with brain damage.
To reach this conclusion, researchers followed 302 high-level male amateur players during eleven matches, collecting blood samples before each match, immediately after, and then 24 to 48 hours later. Cameras were used to count the number of headers performed by each player and estimate their intensity.
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The results show that players who performed headers had higher concentrations of the protein S100B right after the match, compared to those who did not. This protein, produced by star-shaped cells called astrocytes, is used in medicine to assess head injuries.
Additionally, those who performed more than two headers, or particularly powerful headers, also saw an increase in another protein: p-tau217. The latter is one of the main blood markers for Alzheimer's disease. The tau protein normally stabilizes the internal structure of neurons, but mechanical stress can detach it and transform it into p-tau217.
Levels of p-tau217 and S100B returned to baseline within 24 to 48 hours after each match. However, the study authors believe this does not rule out a long-term harmful effect. Other research has also shown that repeated head trauma in soccer players or American football players can kill neurons and cause brain inflammation. The hypothesis is that the effects of headers accumulate over time, contributing to the development of neurodegenerative diseases.
Marsh Köings, co-author of the study, notes that the measured increases do not exceed the thresholds used clinically to diagnose serious injuries. However, these thresholds are designed to detect much more severe trauma. What concerns researchers is the repetition of this action hundreds or thousands of times.
In the meantime, scientists are calling for more studies. Following the same players over an entire season would allow better quantification of the cumulative effect of headers and guide future decisions by sports authorities.