At least one in four former National Football League (NFL) players who died between 2016 and 2021 showed signs of chronic traumatic encephalopathy (CTE), a degenerative a degenerative brain disease associated with repeated head impacts, according to a new study.

The findings add to concerns about the long-term neurological consequences of playing American football, although researchers caution that the results cannot be used to estimate the prevalence of CTE among all current or former NFL players.

The study, published in the BMJ, identified 1,712 deceased former NFL players who died between 2008 and 2021. Out of that total group, 338 brains were donated and evaluated, and 93.2% (315 brains) of those actually examined had neuropathologically confirmed chronic traumatic encephalopathy (CTE).

What Is CTE?

CTE is a progressive neurodegenerative disease associated with repeated head impacts. It is characterised by an abnormal build-up of a protein called phosphorylated tau in the brain.

Unlike a concussion, which can cause immediate symptoms, CTE is diagnosed after death by examining brain tissue. Researchers therefore cannot currently diagnose CTE with certainty in a living person.

The condition has been associated with problems including memory loss, impaired thinking, depression, impulsive behaviour, and difficulties with movement. However, symptoms can vary considerably, and having CTE-related brain changes does not necessarily mean a person would have developed obvious symptoms during their lifetime.

What Did the Study Find?

Among the 1,712 former NFL players identified, 338 had their brains donated for research, and 315 of those examined were diagnosed with CTE.

The likelihood of finding severe CTE increased with the amount of time players had spent playing football.

The severity of the disease also appeared to increase with greater exposure to football. The researchers found that cumulative years of play were associated with more severe CTE pathology, which was in turn associated with greater functional impairment reported before death.

These findings strengthen the evidence of a relationship between repeated head impacts in American football and CTE. However, because brain donation is voluntary and often driven by families noticing symptoms before a player's death, the figures shouldn't be taken as a measure of how common CTE is among all NFL players.

Does This Mean 1 In 4 NFL Players Have CTE?

No. The researchers did not randomly select living or deceased NFL players. Instead, they examined brains donated to research, meaning the sample could be affected by selection bias.

People whose families chose to donate their brains may have been more likely to have experienced neurological or behavioural problems, or to have had concerns about the effects of football.

As a result, the statistic should not be interpreted as meaning that exactly one in four NFL players develops CTE. The study also cannot establish that every neurological or psychiatric symptom experienced by a former player was caused by CTE.

What Do the Findings Mean for Football?

The research adds weight to calls for greater attention to cumulative head impacts in contact sports. Importantly, the results suggest that risk may be related not simply to individual concussions, but to the overall burden of repetitive head impacts accumulated during years of playing.

That does not mean football players should automatically expect to develop CTE. Instead, the findings highlight why reducing unnecessary head impacts and improving player safety remain important.

For former players experiencing persistent changes in memory, mood, behaviour, or thinking, medical assessment can help identify potential causes and appropriate support.

Researchers say further work is needed to understand why some players develop CTE while others with similar exposure do not. For now, the study provides further evidence that repeated exposure to head impacts can have lasting consequences for brain health.

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