Summary:
A collaborative study led by Boston University researchers estimates that nearly 75% of all National Football League (NFL) players who died between 2008 and 2023 had chronic traumatic encephalopathy (CTE) neuropathology. Published in JAMA Network Open, the investigation accounted for selection bias within postmortem brain donations by integrating National Death Index mortality records across 2,362 deceased players. The resulting 74.5% prevalence rate contrasts sharply with community brain banks, where CTE is detected in less than 1% of the general population.
Key Facts:
- Population-Level Prevalence: Adjusting for selection bias across all 2,362 NFL players who died between 2008 and 2023, the study estimates an overall postmortem CTE prevalence of 74.5%.
- Correcting for Donation Bias: Families of players with cognitive symptoms were approximately five times more likely to donate their brains to research, enabling biostatisticians to recalibrate the 94% raw pathology rate observed in the brain bank down to the true population estimate.
- Extreme Elevation Over General Public: In community brain banks across the United States, Australia, Austria, and Brazil, CTE is identified in less than 1% of deceased donors, underscoring the specific risk tied to repetitive head impacts in contact sports.
Source: Boston University School of Public Health
Chronic traumatic encephalopathy (CTE), a progressive neurodegenerative tauopathy linked to repetitive head impacts, has remained at the center of intense scientific, athletic, and public health debates. Because a definitive diagnosis of CTE currently requires postmortem histological examination of brain tissue to identify pathognomonic perivascular clusters of hyperphosphorylated tau, determining the actual prevalence of the disease among professional athletes has historically been hindered by selection bias: families of players who exhibited severe cognitive, mood, and behavioral symptoms in life are far more likely to donate their brains to science.
Now, a multi-institutional study led by investigators at the Boston University School of Public Health, Boston University Chobanian & Avedisian School of Medicine, Mass General Brigham (MGB), and the Concussion & CTE Foundation provides the first population-wide estimate of CTE prevalence across an entire era of professional football.
Publishing in the journal JAMA Network Open, the research team calculated that 74.5% of all former NFL players who died between 2008 and 2023 had CTE neuropathology.
Overcoming the Selection Bias Dilemma
The new study resolves the wide margins of previous estimates. In August 2026, the same research group estimated that between 25% and 98% of NFL players who died between 2016 and 2021 had CTE. That broad range reflected profound uncertainty regarding whether the brains donated to research were representative of the larger NFL retiree community.
To determine the true population prevalence, the team developed a biostatistical modeling approach combining direct tissue evaluations with comprehensive public health records.
Among 387 deceased NFL players directly evaluated in the brain bank, 362 (93.5%) exhibited confirmed CTE neuropathology. The researchers then evaluated National Death Index death certificate data for all 2,362 NFL players who died over the 16-year period between 2008 and 2023, tracking clinical causes of death, documented diagnoses of dementia, and other neurodegenerative illnesses.
By comparing demographic data, playing position, career length, age at death, and reported clinical symptoms between donors and non-donors, the investigators determined that former players with cognitive impairments were five times more likely to have their brains donated than asymptomatic players.
Applying this selection ratio to the entire 2,362-player cohort, the model converged on an adjusted population prevalence of 74.5%.
“Providing a precise estimate for the prevalence of CTE among deceased NFL players helps define the scale of the problem and informs priorities for the potential current and future medical needs of this community,” said lead author Julia Gallini, a PhD candidate at the Boston University School of Public Health. “With CTE consistently found in less than 1% of donors to community brain banks, an estimated 75% prevalence among NFL players who died over a 16-year period is concerning, and suggests we need to increase efforts to support families, diagnose CTE during life, and treat CTE-related symptoms.”
Contextualizing Risk and Symptom Expression
The authors caution that this 74.5% estimate applies strictly to deceased former players across this specific historical window. It cannot predict the exact prevalence among living retirees or active players, who may have experienced different concussion protocols and helmet designs.
Furthermore, the presence of postmortem CTE pathology does not mean every individual experienced functional clinical impairment during life, especially in early-stage disease.
When clinical manifestations do emerge, they typically present as progressive cognitive decline, executive dysfunction, emotional dysregulation, and dementia. Prior epidemiological investigations have shown that former NFL athletes develop clinical dementia at four times the rate of the general population—a risk elevation unmatched by any other known environmental or occupational exposure.
“It’s hard to learn what the guys who built the game have suffered through,” said Matt Hasselbeck, an 18-year NFL veteran quarterback and ambassador for the DIAGNOSE CTE study. “I’m looking at this like getting a scouting report. Now that we know what we’re up against, we have a better chance of winning. I can’t take back the hits I took, but I can sign up for research and do whatever I can to help the scientists so they can find a cure in my lifetime. We have to learn from this data to make the game safer, because we can’t accept these numbers for the next generation of players.”
The Path Toward In Vivo Diagnosis and Intervention
Senior author Yorghos Tripodis, PhD, professor of biostatistics at Boston University School of Public Health, emphasized that defining the scale of the disease provides momentum for clinical care.
“We would like to thank the former NFL player community for their support of this research that is answering an important public health question on the relationship of tackle football and CTE,” said Dr. Tripodis. “We recognize these findings may cause concern for the community of living players and their families. We want them to know that we and others are standing by to provide support, and that we have hope for those living with CTE. Discoveries from the brain bank have already brought us significantly closer to a diagnosis during life, at which point our most important goal will be to develop effective treatments for CTE.”
Clinical neuroscientists emphasize that former athletes experiencing mood, memory, or behavioral shifts should undergo evaluation by clinicians specializing in neurodegenerative care, as proactive management of vascular health, sleep apnea, metabolic function, and psychiatric symptoms can preserve cognitive reserve and enhance quality of life.
Funding
This work was supported by the National Institute of Aging Boston University AD Research Center, P30AG072978, the National Institute of Neurological Disorders and Stroke, U54NS115266, and the Concussion & CTE Foundation.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper will be reviewed in full upon release.
- Additional context added by our staff.
About this CTE Research:
- Media Contact: Gina DiGravio
- Source: Boston University School of Medicine
- Image Credit: Image credited to Neuroscience News
- Original Research is Open Access: The findings will appear in JAMA Network Open
