Heading a soccer ball during recreational play causes short-term spikes in blood proteins associated with brain cell injury and Alzheimer's disease pathology, according to research published in JAMA Neurology and presented this month at the Alzheimer's Association International Conference 2026 in London. The findings come from a team at Amsterdam University Medical Center and apply not just to elite athletes but to everyday amateur players, including the millions of recreational and youth players across the United States.
A separate study presented at the same conference by researchers at Boston University found that longer soccer careers were associated with a higher risk of chronic traumatic encephalopathy, or CTE. Together, the two studies are among the most significant bodies of evidence presented at this year's AAIC on the neurological risks of soccer participation at all levels.
Why This Matters
An estimated 26 million Americans play soccer at some level, and the sport is among the most popular youth activities in the country. Most conversations about brain injuries in youth sports have focused on diagnosed concussions, but the majority of headers do not produce a concussion. The concern now centers on subconcussive impacts, collisions that do not generate a sideline diagnosis but may still be causing measurable biological effects on brain tissue.
If a recreational weekend player or a 12-year-old on a travel team is generating the kind of blood protein elevations documented in this research after a single practice or match, the implications for policy at the youth sports level are significant. The Netherlands' Royal Dutch Football Association already responded to this body of evidence by introducing stricter heading guidelines for youth players beginning with the 2025 to 2026 season. No equivalent national policy exists in the United States, though some youth leagues have voluntarily reduced heading.
What We Know So Far
The primary study, authored by Marloes Ilse Hoppen and colleagues at the Alzheimer Center of Amsterdam University Medical Center, measured blood levels of two proteins, p-tau217 and S100B, in amateur soccer players before and after matches. Both biomarkers are clinically significant. S100B is a calcium-binding protein released specifically by glial cells, the support cells of the brain, when those cells are under stress. P-tau217 is an abnormal, phosphorylated form of tau protein strongly associated with Alzheimer's disease pathology and traumatic brain injury.
Players who headed the ball showed immediate increases in concentrations of both proteins compared to players who did not head the ball during the same match. A clear dose-response pattern emerged: the more frequently a player headed the ball, and the harder the impact, the greater the elevation in both markers. The largest increases were recorded after high-impact headers, defined in the study as contacts where the ball had traveled more than 20 meters through the air before impact.
Critically, blood levels of both proteins returned to baseline within 24 to 48 hours, meaning the effects were acute rather than persistent. A separate 2026 study of approximately 300 male amateur players also found temporary increases in brain-damage markers after heading, with stronger effects tied to frequency and impact force, consistent with the Amsterdam UMC findings.
Where the Risk Is Highest
Youth players in cities across the country from Los Angeles to New York, Chicago to Houston, participate in travel leagues, school programs, and recreational clubs where heading is a standard part of training and match play. The risk is not limited to professional or elite levels. The Amsterdam UMC research specifically studied amateur, recreational-level players and still detected the biomarker elevations.
Younger players are also considered neurologically more vulnerable than adults, as the developing brain has less white matter myelination, making it more susceptible to the mechanical forces produced by subconcussive impacts. Head injuries during adolescence have been associated with greater and longer-lasting effects than equivalent impacts in adults, according to pediatric neurology research. This is why organizations in Scotland, England, and the Netherlands have already moved to restrict or ban heading in youth soccer under a certain age.
The Boston University study on career duration and CTE, presented at AAIC 2026 by Bobak Abdolmohammadi, examined the relationship between longer professional soccer careers and neuropathological findings consistent with CTE at the time of death. CTE can only be definitively diagnosed post-mortem, but the association with repeated head impacts is now supported by a substantial and growing body of research.
What Doctors and Experts Say
Jort Vijverberg, a neurologist and principal investigator at Amsterdam UMC, acknowledged the limits of what the research proves while not dismissing what it shows. "We don't know what this study says about permanent damage to the brain," Vijverberg told Amsterdam UMC. "Hitting a fast-moving soccer ball with your head causes something that leads to brain proteins getting into the blood. We can't be sure it is direct damage to the white matter, as we see in CTE, or some other effect, but it is hard to ignore."
Caleigh Grace Lynch, lead author of the elite player brain health study presented at AAIC 2026 and a research technician at Imperial College London and the UK Dementia Research Institute, said the findings from former elite players suggest there may be measurable effects on brain health even in midlife, before clinically apparent neurodegenerative disease would typically emerge.
Independent researchers have emphasized that this is not a call for panic, but for prevention. As a June 2026 Medscape review noted, biology records what memory does not. Biomarker and imaging studies are beginning to show what parents and coaches cannot see on the sideline.
What the Evidence Shows and What It Does Not
The JAMA Neurology study measured acute blood protein changes after amateur match play. It documented a dose-response relationship between heading frequency, heading impact intensity, and biomarker elevation. It found that these changes are temporary, resolving within 24 to 48 hours. What the study did not do is follow players longitudinally to determine whether repeated exposures over a career produce lasting neurological changes.
The CTE-duration study at AAIC 2026 examined associations in former players and cannot be used to establish causation or predict individual outcomes. A June 2026 study published in JAMA Network Open that examined adolescent male soccer players over one season found no statistically significant differences in cognition, behavior, or brain structure compared to noncontact sport athletes at that time scale, suggesting the risk picture may be more complex and dependent on cumulative exposure over years rather than single seasons.
MedicalDaily Evidence Check
The Amsterdam UMC study is a case-control study of amateur soccer players published in peer-reviewed JAMA Neurology in 2026 (DOI: 10.1001/jamaneurol.2026.1224), comparing blood biomarker levels in players who headed the ball against those who did not during the same match. The research found that heading was associated with acute elevations in S100B and p-tau217 blood proteins, with a dose-response relationship tied to heading frequency and impact force.
What the study did not prove is whether these acute, reversible elevations translate to long-term neurological damage over a career, as the biomarker changes returned to baseline within 24 to 48 hours and no longitudinal follow-up was conducted. Readers should know that the findings are real-world and occurred in recreational amateur players, not just elite athletes, making them directly relevant to youth leagues and recreational clubs across the United States.
Who Faces the Greatest Risk
Children and adolescents face the highest theoretical risk based on developmental neurology. Youth players whose brains are still developing, typically under age 18, have been identified as the primary target population for precautionary restrictions in countries that have already acted. Adults who head the ball at high frequency, such as professional or semi-professional center-backs and strikers, represent the next most studied group. Players with a personal or family history of Alzheimer's disease, given the p-tau217 connection, may warrant particular attention in future research.
There is no established threshold of heading exposure below which risk is definitively zero. The dose-response nature of the current findings suggests that fewer and less forceful headers produce smaller biomarker responses, which is the biological rationale behind limiting rather than eliminating heading in youth sports policy.
Symptoms and Warning Signs to Watch For
Parents, coaches, and players should be aware that subconcussive impacts do not produce the dramatic sideline symptoms of a concussion. However, a pattern of repeated complaints of headache, visual disturbances, difficulty concentrating, unusual irritability, or memory lapses after practices or games warrants medical evaluation. Any diagnosed concussion in a young soccer player should prompt a full return-to-play protocol and a discussion with a sports medicine physician or pediatric neurologist about heading exposure going forward.
What You Can Do Now
Parents of youth players can ask their child's league or club whether heading restrictions are already in place and, if not, advocate for their adoption. Leagues and schools can consult the policy frameworks already developed in the United Kingdom, Scotland, and the Netherlands, which provide age-graded restrictions on heading in training and match play. The Alzheimer's Association has called for youth sports organizations to take precautionary action in response to the AAIC 2026 findings.
For recreational adult players, limiting high-impact headers during practice, particularly those involving long-range balls, represents the most direct way to reduce the biomarker response documented in this research. Players who experience head impacts during matches should report any symptoms to a clinician and take any necessary rest periods seriously.
Cost and Access: What Patients Should Know
No specific clinical test for subconcussive injury from soccer is currently commercially available as a routine tool. The p-tau217 blood test used in the Amsterdam UMC research is primarily a research and emerging clinical diagnostic tool for Alzheimer's pathology, not yet standard at most community practices. Sports medicine consultations, neuropsychological testing, and advanced brain imaging such as diffusion MRI remain available through academic medical centers and sports medicine programs for players or families with significant concerns.
What Happens Next
Amsterdam UMC has announced continued follow-up research on heading, including studies involving women's soccer players, with support from the Royal Dutch Football Association. The Alzheimer's Association is expected to issue updated guidance on contact sports and brain health. Researchers at Boston University's CTE Center are continuing to investigate the neuropathological profile of former soccer players. MedicalDaily will follow this research as it develops through the fall.
The Bottom Line
The evidence is not yet sufficient to call soccer unsafe or to recommend that all players stop heading the ball. What it does show, clearly and now in a peer-reviewed publication, is that heading even at recreational levels produces short-term measurable biological changes in the blood consistent with brain cell stress, and that longer careers correlate with greater neuropathological risk. The most defensible response today is to reduce heading exposure in youth players and to support research that will clarify what cumulative lifetime exposure means for long-term brain health.
