Study: At Least 1 in 4 NFL Players Develops Brain Disease CTE
A landmark study published Tuesday in The BMJ has found that at least one in four former National Football League players who died between 2016 and 2021 had chronic traumatic encephalopathy (CTE), a progressive degenerative brain disease linked to repeated head impacts. The findings, which could represent a significant underestimate, have been described by researchers as a “wake-up call” for the NFL and the broader football community.
The study, conducted by researchers at Mass General Brigham, Boston University, and the Concussion & CTE Foundation, analyzed 878 former NFL players who died during the six-year period. Of the 235 players whose brains were donated for examination, 215—or 93.2 percent—were found to have CTE, according to NPR.
What the Study Found
Researchers extrapolated the findings to the full cohort of 878 deceased players, estimating a minimum CTE prevalence of 24.5 percent. At the maximum possible estimate, the figure could be as high as 97.7 percent, with the true rate likely falling somewhere in between.
“Somewhere between 24.5 percent and 97.7 percent of NFL players from that time period had this progressive brain disease is a wake-up call for the NFL and scientific communities,” said Dr. Daniel Daneshvar, the study’s lead author and chair of physical medicine and rehabilitation at Mass General Brigham.
The study drew on brain samples from the UNITE Brain Bank at Boston University, examining the deaths of 1,712 former NFL players overall, including 338 who had donated their brains for evaluation. All players in the study were from the NFL’s hard shell helmet era that began in 1949.
By comparison, the rate of CTE in the general population is less than 1 percent, making the findings particularly striking, as The Guardian reported.
Understanding CTE
Chronic traumatic encephalopathy is a progressive, degenerative brain disease caused by repeated impacts to the head. Symptoms include difficulty with attention and memory, dementia, mood disorders, headaches, difficulty walking, emotional instability, and suicidal thoughts. CTE can only be definitively diagnosed after death through brain examination.
The disease was first scientifically linked to football about 20 years ago, and the BU CTE Center has since published more than 100 studies on the condition. High-profile former NFL players including Junior Seau, Dave Duerson, and Aaron Hernandez were all found to have had CTE after taking their own lives.
The study also found a high correlation between dementia and the most advanced stage of CTE (Stage IV), with more than 90 percent of Stage IV samples also diagnosed with dementia, according to ESPN.
Implications for Current Players
If the minimum prevalence rate is applied to today’s players—1,696 on the league’s 32 regular-season rosters, not including more than 500 practice squad members—at least 400 current players would be expected to develop CTE.
Jesse Mez, coauthor of the study and codirector of clinical research at the BU CTE Center, said the findings should serve as a call to action. “If at least 25 percent of NFL players who died had these changes in their brain, then this seems like a call to action for more discussion about risk, more research, and more support for affected families,” Mez said, as reported by Boston University’s The Brink.
Mez also noted that because there is a “rather linear dose-response relation between the amount of play and risk for CTE,” higher prevalence might also be expected among college and high school players.
League and Players’ Union Response
An NFL spokesperson said the league “continuously strives to make the game of football safer, including by implementing strategies to reduce concussions and head impacts,” adding that the NFL remains committed to providing resources to enhance players’ physical and mental well-being.
The NFL Players Association issued a stronger statement, calling the study “a sobering reminder that football carries real risks, and those risks can have lasting consequences for players and their families.” The union said the findings “should serve as a call to action across the entire football ecosystem.”
Houston Texans linebacker Azeez Al-Shaair, entering his eighth NFL season, acknowledged the risks inherent in the sport. “The reality of the game is that it’s aggressive. It’s violent,” he said. “We’re out here running at each other. These are the best athletes in the world playing on one field. You’re going full speed running into each other. That’s the type of stuff that can happen.”
Expert Analysis and Prevention
Daneshvar emphasized that the bulk of head impacts experienced by former NFL players did not occur at the professional level. “They occurred at the collegiate level… and at the high school level and in many cases the youth level,” he said. “And all of those cumulative hits to the head added up to result in an increased risk.”
Nearly 70 percent of head impacts occur during practice, Daneshvar noted. “So without changing a single minute of game time at any of those levels, we can be substantially reducing the cumulative head impact burden that these individuals are experiencing throughout their lives,” he said.
Rachel Grashow, director of research initiatives at Harvard’s Football Players Health Study, who was not involved in the study, expressed concern that public discourse around CTE may be creating hopelessness among living former players. “Our concern is that the public and kitchen table conversations around CTE are creating hopelessness in living former NFL players,” Grashow said, noting that treatable conditions such as sleep apnea, high blood pressure, and low testosterone can cause symptoms commonly associated with CTE.
Dr. Randall Chesnut, a neurological surgeon at the University of Washington who was not involved in the research, praised the study’s methodology but cautioned that the findings may not fully represent the modern NFL. “It was captured during a time when there was delayed recognition by the NFL that concussion was a big deal,” he said. “So this may not represent the NFL in 2026.”
Broader Context
The study comes amid growing scrutiny of football’s long-term health consequences. A previous BU-led study of nearly 20,000 NFL players, published in July 2026, found that football players were four times more likely to die of neurodegenerative diseases including ALS, dementia, and Parkinson’s disease than the general population.
The NFL has taken steps to improve player safety, including the 2011 collective bargaining agreement that limited contact practices during the season, and the league’s approximately $1 billion settlement of concussion-related lawsuits in 2016. The Ivy League banned full-contact tackling during practices in 2016.
Writing in an accompanying editorial, professors Tobias Kurth of the University Medical Center Berlin and Richard Riley of the National Institute for Health and Care Research in Birmingham praised the study, calling it “one of the most informative estimates to date” regarding CTE prevalence among NFL players, as France 24 reported.
What’s Next
The researchers hope to produce a subsequent paper in the coming months estimating the overall rate of CTE in all NFL players at the time of their death. There is currently no way to diagnose CTE in living patients, though BU researchers are working on projects to change that, including Bank CTE, a major study following people aged over 40 who played an organized or collision sport or served in the military.
Mez emphasized that help is available for those concerned about their health. “We recognize that these findings will be concerning for NFL players and their families, and we want them to know that help is available,” he said. “We have treatments for many symptoms believed to be associated with CTE, and in our clinic, we find that symptoms can improve with proper medical care.”
As the scientific understanding of CTE continues to evolve, the study underscores a fundamental question facing American football at every level: how to balance the sport’s inherent physicality with the long-term health of those who play it.