What Is the Connection Between CTE and Soccer?

Former professional soccer players die of neurodegenerative disease at roughly three and a half times the rate of the general population, and the most likely explanation involves the sport’s signature move: heading the ball. Whether that neurodegeneration takes the specific form of chronic traumatic encephalopathy, or CTE, is harder to confirm, because CTE can only be diagnosed by examining brain tissue after death. A handful of confirmed CTE cases in retired soccer players exist, but the broader picture of elevated dementia, Alzheimer’s disease, and motor neuron disease risk among former players is supported by large-scale studies that have reshaped how the sport thinks about head impacts.

How Big Is the Risk?

The most influential study on this question tracked over 7,600 former male professional soccer players in Scotland against more than 23,000 matched members of the general population. Over a median follow-up of 18 years, about 5% of the former players received a neurodegenerative disease diagnosis, compared with roughly 1.6% of controls. That translated to a hazard ratio of 3.66, meaning the former players were diagnosed at nearly four times the rate.¹ A related analysis of the same cohort found that neurodegenerative disease was listed as the primary cause of death for 1.7% of former players versus 0.5% of controls. The risk was not evenly distributed across diseases: Alzheimer’s disease showed the largest gap (about five times higher among players), while Parkinson’s disease showed a smaller but still significant elevation (about twice the rate).²

These numbers are striking, but they describe overall neurodegenerative disease, not CTE specifically. Only a few cases of CTE in retired soccer players have been confirmed through post-mortem neuropathological examination.³ That small number reflects practical limitations more than a genuine rarity: families must consent to brain donation, and until recently few researchers were looking for CTE in soccer players at all. The disease has been studied far more extensively in American football and boxing, where brain banks have been collecting tissue for decades.

What Heading Does to the Brain

The leading theory is that a combination of repeated sub-concussive and concussive injuries, from both heading the ball and colliding with other players, gradually damages the brain over a career. No single header is thought to be catastrophic on its own. The concern is cumulative exposure: thousands of low-level impacts adding up over years.⁴

One way researchers gauge the potential harm is by measuring how much the brain moves and deforms during a header. A study using instrumented mouthguards found that the average peak linear acceleration during a soccer header was about 26 g, with peak angular accelerations around 1,730 rad/s². Some of those values overlapped with brain injury metrics recorded in American football, which caught researchers’ attention.⁵ That does not mean every soccer header is equivalent to a football tackle, but it suggests that the forces involved are not trivial.

Blood-based biomarkers offer another window. In one small study, a protein called neurofilament light (NfL), which leaks into the blood when nerve fibers are damaged, rose by about 26% an hour after a heading session. Intriguingly, NfL levels were still elevated three weeks later, averaging over three times baseline values.⁶ However, a larger study analyzing 354 blood samples found no effect on NfL from short-term heading exposure, though tau, a different brain injury marker, did rise after both high-intensity exercise and repetitive headers.⁷ The conflicting results on biomarkers are a theme throughout this field. The signal is there, but it flickers depending on the study design, the number of headers, and how soon after impact blood is drawn.

Some imaging studies have found associations between heading and abnormal brain structure, though the data remain preliminary. Studies looking at cognitive function in active players have produced mixed results: some find subtle impairments tied to heading volume, while others do not.⁸ One longitudinal study of professional players found no evidence of cognitive impairment compared with non-athletes over a year of follow-up, and heading exposure did not correlate with test performance.⁹ This is the kind of result that makes researchers cautious: the long-term epidemiological data clearly shows elevated risk decades later, but catching the damage in real time during a player’s career has been difficult.

Does Heading Frequency Matter?

Yes, and this is one of the clearest findings in the field. A 2023 study of retired male professional soccer players found a dose-response pattern: players who reported heading the ball more than 15 times per match had roughly 3.5 times the odds of cognitive impairment compared with those who headed five or fewer times. When heading frequency in both matches and training was combined, the highest-frequency group had nearly five times the odds of impairment.¹⁰

Field position offers a crude proxy for heading exposure. The Scottish cohort data showed that defenders, who head the ball frequently in clearances and aerial duels, had the highest risk of neurodegenerative disease. Goalkeepers, who rarely head the ball at all, had the lowest risk, and their elevation over the general population was not statistically significant.¹ The goalkeeper finding is revealing. If the excess risk were caused by something about professional soccer in general, like stress, supplements, or turf chemicals, goalkeepers should share the elevated risk. The fact that they largely do not suggests the connection runs through head impacts specifically.

Concerns for Young Players

If cumulative exposure drives the damage, then how early a player starts heading matters. Youth soccer has attracted particular scrutiny. A study of female youth soccer players used computational models to estimate brain strain during purposeful heading and found that deep brain structures, including the corpus callosum, thalamus, and brainstem, experienced strain during routine headers. The strain in these regions was strongly associated with rotational velocity of the head rather than straight-line acceleration.¹¹

A study of youth academy players found that certain types of headers, particularly those played in aerial duels and from long distances, were associated with slower improvement in psychomotor speed and reaction time over two seasons of play. The more of these forceful headers a young player performed, the less their cognitive processing speed improved over time compared with peers who headed less.¹² That finding is subtle but concerning: it is not that young players are getting worse, but that their expected developmental gains are being blunted.

Several national federations have responded by restricting heading at younger ages. U.S. Soccer prohibited heading for children under 10 and limited it in training for players aged 11 to 13 starting in 2015. The English FA introduced similar guidelines. Scotland, where the landmark epidemiological data was collected, recommended limiting heading in training across all age groups. These policies vary in enforcement, and their long-term impact on neurodegenerative disease rates will take decades to evaluate.

Why Female Players Face Additional Risk

Female soccer players experience concussions at a higher rate than their male counterparts. A scoping review identified several overlapping explanations: women tend to have smaller head and neck dimensions and lower neck strength, which means the head decelerates more during an impact. Hormonal differences and structural differences in brain tissue may also play a role, along with differences in visual awareness and preparedness for contact.¹³

The relationship between physical attributes and head acceleration has been tested directly. In a study of 100 soccer players performing controlled headers, head and neck size explained about 22% of the variation in linear acceleration, and neck strength explained another 13%. Heading technique, interestingly, did not significantly predict head acceleration once size and strength were accounted for.¹⁴ This has implications beyond sex differences. Any player with a lighter head or weaker neck, including younger players of any sex, experiences greater brain acceleration from the same ball impact.

The Connection to ALS

The neurodegenerative risk for soccer players is not limited to dementia and CTE. Amyotrophic lateral sclerosis, or ALS, has shown up at unusually high rates among professional soccer players. An Italian study of over 7,300 professional players found five ALS cases during follow-up, against an expected count of less than one. The overall risk was about 6.5 times higher than expected, and it increased with career length: players with more than five years of professional play had about 15 times the expected risk.¹⁵

A broader review of the evidence found that professional sports with repetitive head and neck trauma, a category that includes soccer, were associated with an ALS risk about 8.5 times higher than the general population. Non-professional versions of the same sports did not show this elevation, and neither did professional sports that do not involve head trauma.¹⁶ A separate review of the evidence noted that ALS onset in soccer players occurred about 24 years younger than in the general European population, and the risk was highest among outfield players, particularly defenders, rather than goalkeepers.¹⁷ Whether this ALS risk stems from the same repetitive brain trauma that drives dementia, from spinal cord impacts, or from some other factor related to professional athletics remains an open question.

Why Lifestyle Factors Don’t Explain the Gap

An obvious question is whether the elevated dementia rates among retired players might be driven by post-retirement factors like alcohol use, diabetes, physical inactivity, or other known dementia risk factors. A 2024 study tackled this directly, comparing rates of common lifestyle-related dementia risk factors between former professional soccer players and matched controls. The answer was clear: former players had similar or lower rates of conditions like diabetes and hypertension compared with the general population. The dementia risk associated with those factors among players was similar to or lower than among controls. The authors found no evidence that modifiable health and lifestyle factors explained the elevated dementia rates.¹⁸ If anything, retired professional athletes tend to be healthier than the average person in many respects, which makes their excess neurodegenerative risk more striking, not less.

What Makes CTE Research in Soccer Difficult

CTE, in the strict pathological sense, is defined by a specific pattern of abnormal tau protein deposits in the brain. Confirming it requires a post-mortem examination by a neuropathologist. This creates an immediate selection problem: the brains available for study come disproportionately from players or families who suspected something was wrong. A study examining this issue in American football found that selection bias meaningfully skews the apparent prevalence of CTE in brain bank research.¹⁹ The same logic applies to soccer. We cannot say what percentage of former soccer players develop CTE, because the sample of donated brains is not random.

Beyond the selection problem, the symptoms commonly attributed to CTE, such as memory loss, depression, impulsivity, and difficulty with executive function, overlap heavily with many other conditions. Normal aging, substance abuse, sleep disorders, the psychological adjustment to retirement, and pre-existing mental health conditions can all produce similar presentations. A review of the factors that influence these symptoms concluded they should be considered as potential modifiers of clinical outcomes within a broader framework that includes developmental, demographic, and lifestyle variables.²⁰ In other words, when a retired player develops memory problems at 60, it is often impossible to say with certainty that repetitive heading caused it, even if the population-level data shows heading increases the probability.

Can Prevention Strategies Reduce the Risk?

The most intuitive intervention is strengthening the neck, since stronger neck muscles should stabilize the head during a header and reduce brain acceleration. That reasoning is backed by the biomechanical data showing that neck strength predicts head acceleration. But when researchers actually tested a neck-strengthening program in soccer players, the trained group did not show significant reductions in head acceleration or other impact metrics during subsequent heading compared with controls.²¹ The gap between the observational finding that stronger necks correlate with lower acceleration and the interventional finding that deliberately strengthening the neck doesn’t reduce heading forces is puzzling. One possible explanation is that the players who naturally have bigger, stronger necks benefit from skeletal and muscular attributes that a few weeks of training cannot replicate.

Heading technique instruction has also been studied. A program called Get aHEAD Safely in Soccer™ was tested in youth female players. While coaches reported visible improvements in heading form, the measured head impact biomechanics did not change significantly from pre-season to post-season. The researchers suggested that lighter soccer balls might be a more practical addition to training, since reducing ball mass directly reduces the forces transmitted to the head.²²

Ball characteristics matter more than people might think. A systematic review found that reducing ball mass by 20 to 32% lowered peak linear accelerations by about 9 to 10%, with similar reductions in angular acceleration and neck loading.²³ The physics are straightforward: a lighter ball imparts less force. Whether this translates to meaningful long-term protection is unknown, but for youth training environments where heading is being introduced, lighter balls represent one of the few interventions with a clear biomechanical rationale.

The most effective approach, at least in theory, is simply heading the ball less often. The dose-response pattern in the epidemiological data makes a strong case for exposure reduction. Limiting headers in training, restricting heading at young ages, and considering rule changes that reduce the frequency of long aerial clearances in matches are all on the table. Some of these changes are already happening at the youth level. Whether professional leagues and senior competitions will follow remains a more contentious conversation, since heading is woven into the tactical fabric of the sport in ways that are difficult to legislate away without changing how the game is played.