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A statistical model estimated that 74.5% of former NFL players who died from 2008 through 2023 had CTE, adjusting for selective brain donation. The estimate concerns deceased players in that period, not all NFL players, living players, or athletes in other sports; it also does not show CTE stage or predict an individual’s symptoms.
A statistical model estimates that 74.5% of former NFL players who died from 2008 through 2023 had chronic traumatic encephalopathy (CTE), after accounting for the likelihood that families of players with cognitive symptoms were more likely to donate their brains. The estimate, reported in JAMA Network Open, applies to deceased former players in that period—not to all NFL players or those still living.
Yorghos Tripodis, PhD, of the Boston University School of Public Health, and colleagues combined data from the UNITE brain bank with National Death Index records. Among 2,362 former players who died during the study period, 396 were recorded as brain donors. The report’s analysis included 387 donors with the relevant information; 362 of those 387, or 93.5%, had CTE identified at autopsy.
Because brain donors are not a random sample, the team used a statistical selection ratio to estimate how donation patterns could affect the result. The median ratio was 4.97, meaning families of players with cognitive symptoms were estimated to be about five times more likely to donate a brain than families of players without those symptoms. After adjustment, the estimated CTE prevalence was 74.5% (95% confidence interval: 69.6% to 78.3%). The model also estimated all-cause dementia prevalence at 27.2% (95% CI: 22.6% to 31.6%).
The researchers said the adjustment reduced, but did not erase, the concern that donor-based estimates overstate prevalence. Their study was cross-sectional, and CTE can currently be identified only by examining brain tissue after death. The reported percentage is therefore a model-based estimate for a defined group and time period, not a diagnosis or direct count of every former player.
What the Estimate Says About NFL Deaths
The study offers a way to estimate CTE beyond the people whose families donated their brains, addressing a major limitation of brain-bank research. The high estimate, even after adjustment, suggests that donation bias alone may not account for the frequency of CTE pathology found among former NFL players whose brains were studied. It adds evidence about a population with repeated exposure to head impacts, while remaining bounded by the study’s method and scope.
The number does not say how many living former players have CTE, how severe their brain pathology is, or whether a particular person will develop cognitive problems. CTE stage is associated with the severity of cognitive symptoms, but this model did not estimate stage. That distinction matters for families, players and clinicians: a population-level estimate cannot determine an individual’s health or care needs.
Harvard researcher Rachel Grashow said the findings also direct attention to the roughly 20,000 living former NFL players, some of whom may have cognitive symptoms or dementia. She said that monitoring and treating other health conditions may help address risks to cognitive and cardiovascular health, though this study did not test those interventions.
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How Brain Donation Shapes the Data
CTE is a brain disease associated with repetitive head impacts, but it can be confirmed only after death through examination of brain tissue. That limits prevalence research: studies relying on donated brains can describe pathology in donors, but donors may differ from all former players. Families may be more likely to donate when a player experienced cognitive or behavioral changes.
In this study, the deceased players had an average of 5.1 years in the NFL, and 41.1% were at least 80 years old when they died. The analysis focused on former NFL players who died from 2008 through 2023. Outside experts quoted by MedPage Today said those findings should not be generalized to athletes in other sports or to people who played football at lower levels, whose exposure patterns may differ.
“Selection bias materially inflates donor-based prevalence estimates but is unlikely to fully explain the high burden of CTE neuropathology among this population.”
— Yorghos Tripodis and co-authors
Who the 74.5% Estimate Leaves Out
The estimate does not include living players and cannot establish how many of them have CTE. It also does not report CTE stage, which limits what it can say about the likely severity of pathology or a person’s day-to-day functioning. Because CTE is diagnosed after death, the study cannot provide a routine clinical test result for an individual living player.
The model depends on assumptions about selection into brain donation, including that donation was primarily driven by cognitive symptoms and that symptoms were captured through dementia on death certificates and adjustments for mild cognitive impairment. Independent experts said those assumptions matter when interpreting the result. The study also does not estimate prevalence among college, high school or other sports participants. How well its results would apply to those groups is unknown.
Attention Turns to Living Players
The study does not set out a new clinical screening program or a next research milestone. Further research would be needed to test the modeling assumptions, estimate disease patterns in living players, and assess how findings vary by CTE stage and football exposure. The authors’ estimate should be read as a result for former NFL players who died during the specified years, rather than as a forecast for current players.
Grashow pointed to ongoing work involving more than 5,000 former players in Harvard’s Football Players Health Study. She said the group’s work examines potentially treatable conditions—including sleep apnea, high blood pressure, depression and anxiety—that can affect cognitive health. What the new prevalence estimate means for individual players, and whether the model can be extended reliably to other populations, remain open questions.
Key Questions
What did the new study estimate?
It estimated that 74.5% of former NFL players who died from 2008 through 2023 had CTE, after adjusting for selective brain donation. The estimate came from a statistical model, not direct examination of every player who died.
Does this mean three in four living NFL players have CTE?
No. The study covered former players who died during the study period. It did not estimate CTE prevalence among living players.
Why was an adjustment for brain donation needed?
Families may be more likely to donate a player’s brain if the player had cognitive symptoms. Since donors may not represent all former players, the researchers modeled that selection pattern to adjust the estimate.
Can the study say how severe CTE was?
No. The model estimated the proportion with CTE, but it did not estimate CTE stage. The findings also cannot predict an individual player’s symptoms or prognosis.
Do the findings apply to college or youth football players?
No prevalence estimate for those groups was provided. The study focused on former NFL players who died from 2008 through 2023, and its results should not be assumed to apply to athletes at other levels or in other sports.
Source: medpagetoday.com
