Heading a soccer ball just once is enough to raise levels of proteins associated with brain damage

Heading a soccer ball just once is enough to temporarily release proteins into the blood that are associated with damage to brain cells, a new study suggests.

For two of the six proteins tracked, their levels rose higher the more frequently and the harder soccer players headed balls. The study authors say that while this could be evidence of acute brain injuries, further studies are needed to determine whether the cumulative effects of heading could increase a player's risk of developing a neurodegenerative disease like Alzheimer's.

In the research, published May 18 in the journal JAMA Neurology, researchers at Amsterdam University Medical Center found that amateur soccer players who headed balls had higher concentrations of the protein S100B in their blood right after a match compared with players who didn't perform headers. S100B, which is produced primarily by star-shaped cells called astrocytes, is widely used to assess for traumatic brain injury (TBI) and usually increases within one hour following a TBI.

Players who performed more than two headers, as well as those who struck multiple high-impact headers, also immediately experienced increases in a protein called p-tau217. This protein is one of the main blood-based signatures, or biomarkers, for Alzheimer's disease.

Tau is a protein that normally helps stabilize the internal scaffolding of neurons, but mechanical stress on the brain's transmission cables detaches it as enzymes then modify the protein, turning it into one of several forms of p-tau, including p-tau217.

Levels of p-tau217 and S100B returned to their original levels within 24 to 48 hours after each match, but the study authors said this does not exclude lasting harm.

"The evidence we have so far suggests that brain damage is occurring from heading soccer balls, both short and long-term," said Samantha Bureau, assistant executive director of the Concussion Legacy Foundation Canada (CLFC), who wasn't involved in the new study. "Long-term consequences are more difficult to track due to the latency between exposure and symptom onset, but several studies have raised concerns about the risks associated with heading in soccer," she told Live Science in an email.

This latest study in the Netherlands incorporated blood samples from 302 higher-level amateur male soccer players taken over the course of 11 matches ‪—‬ before, immediately after, and between 24 and 48 hours after each match. While 86 participants opted not to participate in the third blood draw, study co-author Marsh Königs, an assistant professor of developmental neuroscience at Emma Children's Hospital at Amsterdam UMC, told Live Science that this is unlikely to have affected the results. The study also relied on cameras to record how often each player headed the ball and to estimate the intensity of each header.

Königs said they don't know exactly how headers caused the two biomarkers to rise. However, there are a few potential explanations. The head's acceleration and deceleration within a short time frame could cause a "concussion-like" effect on a much smaller scale, Königs said. Another study, published in April, showed that when someone's head makes contact with a ball, a pressure wave travels through their head.

Regardless of the precise mechanism, scientists hypothesize that the effects of heading accumulate over time, contributing to neurodegenerative disease. A 2025 study found that years of repeated head trauma in soccer and football players kills neurons and leads to brain inflammation.

"It's not the rise in biomarkers itself but rather what it reflects, which is concerning," Königs said. What's more, Königs thinks repeating the team's study among the world's best soccer players would lead to more pronounced results.

Peter Theobald, a medical engineer leading research on brain biomechanics at Cardiff University who was not involved in the study, told Live Science in an email that soccer governing bodies, such as England's Football Association, are reducing the permitted practice loads for headers, despite a lack of meaningful evidence that prescribes a "safe"' level of heading. It is challenging to say whether the biomarker concentrations measured in the Dutch study were enough to cause concern, he added.

According to Königs, the elevations they observed do not exceed thresholds used in clinical settings to diagnose injuries. However, "these cutoffs are mostly designed to detect much more serious injuries, such as severe brain injuries or dementia," he noted. Königs is concerned that issues could arise if this action is repeated hundreds or thousands of times.

"This is a relatively strong study, as it also features athletes from non-contact sports and so does provide confidence that heading is the cause of change," Theobald said. "Tracking the same players throughout a season would have been interesting for example, as this would have enabled reporting of the cumulative effect of heading."

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