Researchers from Boston University and Mass General Brigham reported that nearly 75% of former National Football League (NFL) players who died between 2008 and 2023 had chronic traumatic encephalopathy (CTE). The degenerative brain disease, which is linked to repeated head impacts, can only be definitively diagnosed after death through the examination of brain tissue.
The study analyzed 387 deceased former players and found CTE pathology in 362 of them. To account for selection bias—the fact that families are more likely to donate the brains of players who exhibited cognitive symptoms—researchers applied a statistical adjustment. Without this adjustment, the observed prevalence among donors was 94%; after factoring in that symptomatic players were five times more likely to be donors, the researchers estimated the overall prevalence at 74.5%.
A secondary analysis focused on the years 2016 to 2021, a period with higher donation rates. During this window, 878 former NFL players died, and 235 donated their brains. Of those donors, 215 (91.4%) had CTE. Researchers established a range for this period, noting that even if the 215 confirmed cases were the only ones among all 878 deaths, the prevalence would be 24.5%. In the general population, CTE is found in less than 1% of community brain bank donors.
Former players may notice a shift in how their health is monitored, as the authors recommend seeking specialized clinical evaluations for cognitive or behavioral changes. The findings suggest that current diagnostic methods, which often rely on death certificates, may be insufficient; the study found that only 40.6% of donors with clinician-diagnosed dementia had the condition listed as a cause of death. Consequently, players and their families might see an increased emphasis on identifying modifiable risk factors and seeking treatment for symptoms like cognitive impairment, which the researchers state can improve with proper medical care.
The study used statistical weighting to estimate disease prevalence in populations where direct measurement is impossible. In response to these findings, the NFL stated it will continue implementing strategies to reduce head impacts, such as rule changes and equipment updates like Guardian Caps. The NFL Players Association (NFLPA) indicated it would continue investing in research and expanding access to care through resources like The Trust and the Professional Athletes Foundation. Future research is expected to focus on athletes who played more recently to determine if recent safety changes have impacted these prevalence rates.