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A statistical model estimated that 74.5% of former NFL players who died from 2008 through 2023 had CTE, after adjusting for differences between players whose families donated their brains and those who did not. The estimate concerns deceased former NFL players, not living players or athletes in other sports, and it does not show the severity of CTE in individual cases.
A statistical model estimates that 74.5% of former NFL players who died from 2008 through 2023 had chronic traumatic encephalopathy (CTE), according to a study published in JAMA Network Open. The estimate adjusts for the fact that families may be more likely to donate a player’s brain when they observed cognitive problems, but it applies only to deceased former NFL players—not to living players or football players generally.
Yorghos Tripodis, PhD, of the Boston University School of Public Health, and colleagues combined records from the UNITE brain bank and national death records. Their analysis covered 2,362 former NFL players who died during the study period. Of those, 396 were brain donors; the researchers had usable CTE assessments for 387 donors, and 362 of those 387 (93.5%) had CTE identified at autopsy.
Because brain donors are not a random sample of all deceased players, the team used a statistical adjustment. The model estimated a 74.5% prevalence at death, with a 95% confidence interval of 69.6% to 78.3%. It also estimated that former players with cognitive symptoms were about five times as likely to have their brain donated as those without symptoms. The researchers estimated all-cause dementia prevalence at 27.2% (95% confidence interval 22.6% to 31.6%).
The study’s authors said the findings suggest that selection bias raises prevalence estimates based only on donated brains, but likely does not fully account for the high level of CTE pathology found among donors. The work estimates prevalence across a particular group and period; it does not establish that football caused every case, predict an individual player’s health, or determine how severe the condition was in each person.
What the Estimate Says About Risk
The new estimate addresses a central problem in CTE research: the brains available for study may disproportionately come from people whose families noticed cognitive or behavioral symptoms. A model that accounts for that difference can offer a more informative estimate for the group studied than simply reporting the share of brain donors with CTE. Still, the result remains an estimate shaped by the model’s assumptions, rather than a direct examination of every former player.
The findings matter amid concern about the health of former players. Rachel Grashow, PhD, MS, of Harvard, told MedPage Today that the results refocus attention on the roughly 20,000 living former NFL players, some of whom have cognitive symptoms or dementia diagnoses. She said care for treatable conditions, including sleep apnea, high blood pressure, depression and anxiety, may be relevant to reducing broader health risks. That is a call for attention to player health, not evidence that treating those conditions prevents or cures CTE.
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How Brain Donation Shapes Estimates
CTE is diagnosed by examining brain tissue after death, so researchers cannot use the same method to confirm the condition in living players. Studies relying on donated brains therefore describe a selected group, and the fraction of donors with CTE cannot automatically be treated as the fraction among all former players. The new analysis sought to address that gap by estimating how donation patterns related to cognitive symptoms.
The study group included former NFL players who died between 2008 and 2023. Their mean time playing in the NFL was 5.1 years, and 41.1% were at least 80 years old when they died. The findings do not cover current players, living former players, athletes in other sports, or people who played football at lower levels. An outside expert, Julie Stamm, PhD, of the University of Wisconsin–Madison, said greater exposure to repetitive head impacts has been linked to higher CTE risk, but the study cannot estimate prevalence among lower-level players.
“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, in the study
Limits of the Model and Its Reach
The estimate depends on assumptions about why families donate brains and how cognitive symptoms appear in records, including dementia listed on death certificates and the study’s adjustment for mild cognitive impairment. Weisskopf said the deaths in the analysis represented about 10% of the former players who could have died during the period, and he cautioned that CTE might be less common among players who were still alive. The model cannot directly establish what those living players’ eventual outcomes will be.
The study also does not estimate CTE stage, which ranges across four levels, or show how the estimated cases affected people’s daily lives. It offers no prevalence estimate for other sports or levels of football. The exact prevalence outside this deceased NFL cohort—and how well the model’s assumptions capture donation decisions—remains uncertain.
Following Living Players’ Health
The study provides an estimate for former NFL players who died during a defined period; it does not resolve the prevalence of CTE among people who are alive. Further research would need to follow living players and address how symptoms, medical conditions and eventual brain findings relate over time. Grashow pointed to Harvard’s Football Players Health Study, which has more than 5,000 former players in its cohort, as one source of ongoing research and engagement.
For now, researchers and clinicians can assess former players’ health concerns without treating this population estimate as an individual diagnosis. The study does not set out a new screening or treatment recommendation. Whether future work can produce reliable estimates for living players, or for athletes outside the NFL, remains an open question.
Key Questions
Does the study mean three in four living NFL players have CTE?
No. The 74.5% estimate applies to former NFL players who died from 2008 through 2023. The study did not assess living players, and CTE is identified through examination of brain tissue after death.
How many brain donors in the study had CTE?
Of the 387 donors with CTE assessments, 362, or 93.5%, had CTE identified at autopsy. The researchers adjusted for selective donation to estimate prevalence among all deceased former NFL players in the period.
Why is the 74.5% estimate lower than the donor figure?
Families may be more likely to donate a brain when they have observed cognitive symptoms. The model accounted for that potential selection bias, producing a lower estimate than the percentage among assessed donors.
Does the study show how severe CTE was?
No. It estimates prevalence, but does not provide the players’ likely CTE stages or describe the effects on individual players’ daily lives.
Can the findings be applied to college or youth football?
No prevalence estimate for other sports or lower levels of play was produced. The findings are limited to the deceased former NFL players included in the analysis.
Source: medpagetoday.com
