Researchers from Mass General Brigham published findings in The BMJ establishing the prevalence of chronic traumatic encephalopathy (CTE) among retired NFL players. The study examined former players who appeared in at least one NFL game and died between 2016 and 2021, determining that a minimum of approximately 25% had the degenerative brain disease at the time of death.
CTE can only be definitively diagnosed through brain examination after death, which has historically limited research on the condition’s prevalence. Most prior studies relied on donated brains from individuals or families who suspected the disease based on observed symptoms such as memory loss or mood disturbances. This selection bias created uncertainty about how common CTE actually is among high-risk populations, including professional athletes in contact sports.
The research team, led by Dr. Daniel Daneshvar, utilized the UNITE Brain Bank at Boston University, which contains samples from over 330 NFL players who died between 2008 and 2021, with 93% diagnosed with CTE. To contextualize this sample, researchers compiled a comprehensive list of all players who appeared in at least one NFL game since 1949, cross-referencing demographic data and death certificates from the CDC. This created a denominator of 1,712 players who died during the study period, with analyses focusing on the 2016-2021 window when brain donation rates were highest.
Daneshvar characterized the 25% figure as a conservative estimate, noting the actual prevalence could be substantially higher. The analysis identified additional CTE diagnoses outside the brain bank and 215 former players whose death certificates listed neurodegenerative disease as a cause, despite their brains not being examined. At the upper end, the study calculated a theoretical maximum prevalence of approximately 97% if all unexamined players were assumed to have the disease.
The study also examined the relationship between dementia and CTE severity. More than 90% of players with Stage IV CTE were clinically diagnosed with dementia, but the correlation was substantially weaker for earlier disease stages, with approximately 40% of CTE-free samples also showing dementia diagnoses. Researchers noted that further investigation is needed to develop practical applications for living former players seeking to address potential health concerns.
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