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A study in JAMA Network Open estimated that nearly 75% of former NFL players who died from 2008 to 2023 had chronic traumatic encephalopathy, or CTE. The estimate is based on brain donations and statistical adjustments, not autopsies of every player, and CTE can be confirmed only after death. Researchers estimated that 27% of the players had dementia, which can have multiple causes.
A study published Wednesday in JAMA Network Open estimates that nearly 75% of former NFL players who died from 2008 to 2023 had signs of chronic traumatic encephalopathy, or CTE. The figure is a statistical estimate—not a diagnosis of every player—and researchers say the disease can currently be confirmed only by examining the brain after death.
The researchers combined information from 396 donated brains held by Boston University’s UNITE Brain Bank with national death records for another 1,966 former NFL players. The analysis covered about 2,360 players who died during the 15-year period. About 93% of the donated brains showed signs of CTE, but brain donors are not necessarily representative of all former players.
To account for that potential bias, the team estimated that families of players with cognitive symptoms were about five times more likely to donate a brain than families of players without symptoms. After adjusting for that difference and considering players’ ages at death and estimated rates of cognitive impairment and dementia, the researchers calculated that about 1,760 players, or nearly 75%, had CTE. That is three times the estimate in an earlier study by the same group, which put the share at about one-quarter among players who died over a five-year span.
The study estimated that about 27% of the players had dementia. That figure does not mean dementia was caused by CTE in every case. Study leader Yorghos Tripodis said dementia can have different causes, though he considered CTE a likely contributor in this group. The researchers also emphasized that signs of CTE in the brain do not necessarily mean a person experienced cognitive decline, dementia or other symptoms.
What the Estimate Says About NFL Head Trauma
The findings offer a broader estimate of CTE among deceased former NFL players than a count based only on donated brains, which can overrepresent people whose families noticed symptoms or sought an autopsy. The study’s adjustment attempts to address that selection bias, but the resulting figure remains an estimate because most players in the analysis did not have a donated brain available for examination.
CTE is associated with repeated head impacts and can affect brain regions involved in behavior and emotion. Symptoms may include memory problems, depression and changes in mood, but similar symptoms can occur with other conditions. The distinction matters for players and families weighing what the findings mean: a high estimated rate of brain changes does not establish how many people developed symptoms because of CTE.
The estimate also bears on prevention. Tripodis said reducing brain injuries and impacts could reduce risk. The NFL has said it is working to make the sport safer, citing steps intended to reduce concussions and head impacts, including redesigned helmets and changes to kickoffs. The study did not test whether those measures have reduced CTE rates.
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Why Brain Donations Can Skew CTE Studies
CTE is linked to repeated head impacts, which can cause damage and the buildup of tau protein in the brain, according to Dr. Julian Bailes, a neurosurgeon who was not involved in the study. The condition’s microscopic changes do not appear on routine brain scans. CTE can currently be diagnosed only after death, through examination of brain tissue, limiting researchers’ ability to measure its prevalence in living people.
Earlier research based on donated brains has faced a key limitation: families of people who experienced cognitive or behavioral problems may be more likely to donate a brain or request an autopsy. A previous Boston University study found signs of CTE in 99% of donated brains from former NFL players, a figure researchers have cautioned should not be treated as the rate among all former players. The new analysis sought to account for this selection effect by combining brain-bank findings with records for players who died but did not donate brains.
The study leader, Tripodis, said the estimate surprised him. He told NBC News, “I had to double-check the numbers.” He also stressed that it is a best guess because researchers cannot diagnose CTE in a living person.
““Right now we don’t know how to diagnose CTE when people are alive, so we are trying to estimate.””
— Yorghos Tripodis
What the Study Cannot Establish
The study does not confirm that three-quarters of all former NFL players had CTE: it estimates the share among players who died during 2008–2023, using a statistical adjustment for donation patterns. The researchers did not have autopsies for most of the players included in the calculation, and the estimate depends on assumptions about how symptoms relate to brain donation.
It is also unclear how many players with signs of CTE experienced symptoms attributable to the disease. CTE can be present without recognized cognitive decline, and symptoms such as dementia may have causes other than CTE. The study’s 27% dementia estimate covers dementia from all causes, not a confirmed rate of dementia caused by CTE.
Because diagnosis requires a postmortem brain examination, the findings cannot determine whether a living former player has CTE. The research also does not establish that the league’s cited safety measures have lowered the prevalence of the condition.
Research and Prevention Ahead
Researchers have called for more work on ways to diagnose CTE in living people, which could help clarify how brain changes relate to symptoms and care. Until such a method exists, studies of prevalence will continue to rely on postmortem examinations and estimates based on people who did not have brains examined.
Tripodis said reducing brain injuries and impacts is a prevention priority. The NFL says it has introduced measures including redesigned helmets and a dynamic kickoff rule intended to lower collision speeds. The study does not assess those policies, so their effect on long-term CTE risk remains unknown. Further research will be needed to measure whether changes in exposure to head impacts correspond with differences in disease rates.
Key Questions
What did the study estimate?
It estimated that nearly 75% of former NFL players who died from 2008 to 2023 had signs of CTE. The figure is an estimate, not a direct finding from an autopsy of every player.
How did researchers calculate the figure?
The team analyzed 396 donated brains and death-record information for another 1,966 former players. It adjusted for the likelihood that families of players with cognitive symptoms were more likely to donate brains.
Does having CTE mean a person had dementia?
No. The study says people can have signs of CTE without cognitive decline or dementia. It separately estimated that 27% of the players had dementia, which can have causes other than CTE.
Can doctors diagnose CTE in a living person?
Not currently, according to the researchers and experts quoted in the report. CTE’s defining changes are microscopic and are diagnosed through examination of brain tissue after death.
Did the study show that NFL safety rules reduce CTE?
No. The NFL cited measures intended to reduce concussions and head impacts, but the study did not evaluate whether those measures lower CTE rates.
Source: nbcnews.com
