Three out of four former National Football League players who died between 2008 and 2023 showed signs of chronic traumatic encephalopathy in their brain tissue, according to a Boston University research team. The findings, published on October 28 in JAMA Network Open, correct past statistical limitations by factoring in selection bias among brain tissue donors, yielding an estimated prevalence rate of 74.5% at the time of death.
Boston University Researchers Adjust Selection Bias in UNITE Brain Bank Data
The study analyzed 2,362 former NFL players who died between January 2008 and December 2023 by cross-referencing records from the UNITE brain bank with the National Death Index. Of that total population, 396 individuals donated their brains for research, while 1,966 did not. Among the 387 donors who underwent a complete neurological examination, 362 individuals—or 93.5%—exhibited signs of chronic traumatic encephalopathy.
In the latest study from the BU CTE Center, researchers characterized cognitive symptoms of 33 NFL players antemortem, utilizing neuropsychological testing. This reveals what to expect on neuropsychological tests to aid in diagnosis during life. 🧠🔬 https://t.co/OziAvREOkD pic.twitter.com/39HZ6scUFr
However, Julia Gallini, a doctoral student in biostatistics, and her colleagues noted that raw donation percentages can skew heavily upward. Families are far more likely to donate a deceased relative’s brain if the player experienced cognitive or behavioral symptoms during life. The study calculated that a former player with cognitive symptoms had roughly five times the likelihood of entering the brain bank repository compared to a player without such symptoms.
Conservative Statistical Models and Previous Estimates
To account for this skew, the research team adjusted the donor data against the entire deceased cohort. The resulting prevalence estimate sits at 74.5%, with a 95% confidence interval ranging from 69.6% to 78.3%. A secondary, highly conservative analysis designed to keep the figure as low as possible still placed the prevalence at 63.7%. Sensitivity analyses across eight alternative models produced values ranging from 70.3% to 86.1%.
These figures refine a wide bracket established by previous studies from the same university group. A prior analysis examining over 1,700 former players who died between 2016 and 2021 produced a wide prevalence range spanning from at least 25% to 97.7%. By contrast, brain banks collecting donations from the general population find chronic traumatic encephalopathy in less than 1% of cases.
Pathology and Symptoms Linked to Repeated Head Impacts
Chronic traumatic encephalopathy is a progressive degenerative brain disease driven by repetitive head trauma. Repeated blows prompt an abnormal tau protein to accumulate within neural tissue in a characteristic pattern. Researchers emphasize that severe concussions are not strictly necessary to trigger the pathology, as cumulative sub-concussive hits sustained routinely during play also contribute.
Symptoms frequently manifest years or decades after an athlete’s career ends, making direct attribution difficult. A definitive diagnosis remains impossible during life and requires post-mortem neuropathological examination. The study also estimated that 27.2% of the analyzed former athletes experienced dementia while alive.
Broader Implications Across Contact Sports and Future Research
Senior study author Yorghos Tripodis, a professor of biostatistics, noted that while the findings provide necessary clarity on deceased populations, they do not quantify disease presence among living players. The Boston University research center emphasized that repetitive head impacts extend beyond football, occurring regularly in ice hockey body checks, soccer headers, and among military personnel and first responders.
Gallini stated that precise prevalence metrics help define the true scope of the issue, underscoring the need for improved family support systems, better symptom treatment, and diagnostic methods capable of identifying the disease in living patients.
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