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A study in JAMA Network Open estimates that nearly 75% of former NFL players who died between 2008 and 2023 had chronic traumatic encephalopathy (CTE). The estimate adjusts for the likelihood that families of players with cognitive symptoms were more likely to donate brains; CTE can currently be diagnosed only after death, so the figure is not a confirmed count.
A study published in JAMA Network Open estimates that nearly 75% of former NFL players who died from 2008 through 2023 had signs of chronic traumatic encephalopathy, or CTE. The figure is a statistical estimate—not a confirmed count—because the condition can currently be diagnosed only by examining brain tissue after death, and researchers adjusted for the fact that families of players with symptoms may be more likely to donate brains.
The researchers combined records from 396 donated brains held by Boston University’s UNITE Brain Bank with information on 1,966 other deceased former NFL players. They used players’ ages at death and estimated rates of mild cognitive impairment and dementia in former players over 50 to account for possible differences between those whose brains were donated and those whose brains were not.
About 93% of the donated brains showed signs of CTE. The team estimated that families of players with cognitive decline were about five times more likely to donate a brain than families of players without such symptoms. After adjusting for that potential bias, researchers estimated that roughly 1,760 of about 2,360 players in the study had CTE.
The estimate is three times the one-quarter figure reported in an August study by the same group, which examined players who died over a five-year span. The new study also estimated that about 27% of the players had dementia. That figure refers to dementia from all causes; researchers said CTE was likely to be a cause for some in this population.
What the Estimate Says About Player Risk
The findings add to evidence that CTE may be common among former professional football players, but the estimate does not mean that three-quarters of all NFL players have the disease. It applies to players who died during a specified period and is based on an analysis that combines donated-brain findings with statistical adjustments. The distinction matters because donated samples are not a random cross-section of all former players.
CTE is associated with repeated head impacts, but signs of the disease do not always lead to symptoms. Some people with CTE-related changes may never develop cognitive decline or dementia, and memory or mood symptoms can have other causes. The study therefore cannot establish that every estimated case caused noticeable illness, or that CTE was the sole cause of dementia among players in the analysis.
The work also highlights a major research and care limitation: without a reliable way to diagnose CTE during life, clinicians cannot confirm the condition in a living person. Experts cited in the report said the findings support further research into diagnosis and prevention, including reducing the number of head impacts players experience.
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How Researchers Adjusted Donations
CTE is linked to repeated head impacts. According to neurosurgeon Julian Bailes, impacts can cause the brain to strike or twist against the skull, and repeated injuries may contribute to an accumulation of tau proteins. CTE-related brain changes can involve areas associated with behavior and emotion, but related symptoms—including memory problems, depression and mood changes—can also occur with other conditions.
The disease’s defining microscopic changes do not show up on standard brain scans, so CTE is diagnosed after death. Research based on donated brains has faced criticism because families may be more likely to donate when a player had cognitive or behavioral symptoms. A prior Boston University study found signs of CTE in 99% of donated brains from former NFL players, a result drawn from a selected group rather than a representative sample of all former players.
The new analysis attempted to account for that selection effect by incorporating information on players who died without donating brains. The researchers also compared the estimated prevalence with figures reported for brain-bank donations in the United States, Austria and Brazil, where about 1% of donated brains were said to show CTE. Those comparisons involve different populations and donation patterns, so they do not directly establish an individual player’s risk.
“Right now we don’t know how to diagnose CTE when people are alive, so we are trying to estimate.”
— Yorghos Tripodis
Limits of a Postmortem Estimate
The study does not establish how many living former players currently have CTE. Because diagnosis requires examination of brain tissue after death, the researchers used donated-brain data and statistical modeling to estimate cases among players who died. The estimate depends on those methods and assumptions, including the estimated difference in donation likelihood between families of symptomatic and asymptomatic players.
It is also unclear how many of the estimated CTE cases involved substantial symptoms. The researchers estimated dementia in about 27% of the group, but that category included dementia from all causes. The study cannot show that CTE caused each case, and a finding of CTE-related brain changes does not by itself establish that a person experienced cognitive decline.
The report’s estimate concerns former NFL players who died during 2008–2023, not all professional football players, current players or people who have played other forms of football. The supplied findings do not specify how the estimate would change under different modeling assumptions or whether the same rate applies to other groups.
Diagnosis and Impact Reduction
The study’s authors and outside experts called for more research, particularly into ways to diagnose CTE while people are alive. Until such a method is available, estimates of how common the condition is will continue to rely on postmortem examinations and adjustments for who donates brains.
Researchers also pointed to prevention as the immediate focus. Tripodis said reducing brain injuries and impacts could lower risk. The NFL spokesperson cited measures that include redesigned helmets, such as the Guardian Cap, and a dynamic kickoff rule intended to reduce collision speeds. The source material does not provide evidence about how much these measures have reduced CTE or long-term brain injury, so their effect remains a separate question.
Further studies may help clarify how repeated impacts relate to brain changes, symptoms and dementia, and how representative brain-bank samples are of former players as a whole. For now, the 75% figure should be read as a modeled estimate for a defined group of deceased players—not a diagnosis rate for living NFL players.
Key Questions
What did the study estimate?
Researchers estimated that about 75% of former NFL players who died from 2008 through 2023 had signs of CTE—roughly 1,760 of about 2,360 players in the analysis. It is an estimate adjusted for possible bias in brain donations, not a direct examination of every player.
Can CTE be diagnosed in living people?
According to the researchers and experts quoted in the report, CTE can currently be diagnosed only after death by examining brain tissue. The study’s estimate therefore does not identify which living former players have the disease.
Does having CTE mean a person has dementia?
No. The report says some people with signs of CTE may never develop symptoms. The study separately estimated dementia in about 27% of the players, but that figure includes dementia from all causes and does not establish that CTE caused every case.
Why is the estimate higher than an earlier study?
The earlier study by the same group estimated CTE in one-quarter of former NFL players who died over a five-year span. The new study covered a 15-year period and used donated-brain records plus information on other deceased players to adjust for donation bias. The two estimates cover different time spans and analyses.
What does the NFL say it is doing?
An NFL spokesperson said the league is working to make football safer and reduce concussions and head impacts. The spokesperson cited measures including redesigned helmets and a dynamic kickoff rule; the supplied report does not quantify their effect on CTE prevalence.
Source: nbcnews.com
