An analysis of medical records from more than 2,300 deceased former NFL players estimates that approximately 74.5% likely had chronic traumatic encephalopathy (CTE), a progressive neurodegenerative disease linked to repeated head impacts. The study, published Wednesday in JAMA Network Open, was led by researchers from Boston University, Mass General Brigham, and the Concussion & CTE Foundation. It represents the most comprehensive effort to date to assess CTE prevalence while addressing selection bias—a common challenge in previous research due to reliance on donated brains predominantly from players with cognitive symptoms during life.
The study combined data from 396 donated brains and death records of 1,966 players who did not donate their brains, covering deaths from 2008 to 2023. Nearly 94% of the donated brains showed evidence of CTE, but the researchers adjusted this figure downward to estimate 74.5% prevalence among all deceased players in the cohort.
Researchers said the findings suggest CTE remains prevalent among former NFL players even after accounting for donation bias. Brain donors were more likely to be white, deceased at younger ages, and have longer NFL careers than non-donors, factors that may influence the observed rates.
Additional findings from related research indicate a strong link between severe CTE and dementia. Among brain donors, nearly 60% had dementia, and more than 90% of those diagnosed with Stage 4 CTE—the most severe stage—had dementia. According to study co-author Yorghos Tripodis, this represents one of the largest environmental or occupational increases in dementia risk observed at death.
A separate August study published in the British Medical Journal had estimated that 25% of former NFL players who died between 2016 and 2021 had CTE, a figure considered by its lead author, Daniel Daneshvar, to likely be a low-end estimate with a possible maximum prevalence of up to 97%.
The NFL responded by highlighting ongoing efforts to improve player safety through concussion reduction strategies and encouraged former players to seek medical evaluation for health concerns. The NFL Players Association emphasized the importance of research on football's long-term effects and reaffirmed its commitment to player safety, both during and after playing careers.
Concerns about CTE are also growing beyond the professional level, including among college, high school, and youth football players, although data remain limited since the disease can only be definitively diagnosed postmortem. Notably, Boston University recently diagnosed Hall of Fame NASCAR driver Fred Lorenzen with Stage 3 CTE after his death, marking the first confirmed case in a professional driver.
Researchers involved in the recent study stressed the importance of continued efforts to develop methods for diagnosing CTE in living patients, which could enable clinical trials for treatments and preventive strategies. Julia Gallini, the study’s lead author, emphasized that CTE is preventable, as repeated head impacts are currently the only confirmed risk factor, underscoring the need to limit exposure to head trauma in football and other contact sports.