A study published August 25, 2026, in The BMJ by researchers at Harvard University and Boston University found that at least one in four former NFL players who died over a recent five-year span had chronic traumatic encephalopathy, the degenerative brain disease caused by repeated head impacts. The research, conducted in collaboration with Mass General Brigham, represents a methodological advance over prior CTE studies by calculating prevalence against an entire cohort of deceased players rather than only those whose brains were donated for analysis, producing a minimum population-level estimate that had previously eluded researchers.
Key Takeaways
- The study analyzed deaths of 878 former NFL players between 2016 and 2021; of those, 235 had their brains donated for post-mortem evaluation; CTE was confirmed in 215 of the 235 donated brains (91.4%).
- Using the full cohort of 878 deaths as the denominator rather than only the donated sample, the researchers established a minimum prevalence rate of approximately 25%, the first population-level floor estimate for CTE in former professional football players.
- The NFL Players Association issued an official safety warning to all active roster members, practice squad players, and their agents, stating that repetitive head impacts, including subconcussive hits, cumulatively contribute to degenerative brain disease.
- CTE can only be definitively diagnosed through post-mortem brain tissue analysis; the disease is associated with progressive cognitive decline, memory loss, depression, aggression, and dementia.
- The study arrives weeks before the 2026 NFL regular season opener, adding urgency to ongoing debates about concussion protocols, equipment standards, and the long-term neurological risks of professional football.
The Methodological Shift That Produced the 25% Floor
Prior studies on CTE in football players relied on brain bank data, analyzing only the brains that families chose to donate for research. That approach produced alarming numbers, including a widely cited 2017 Boston University study published in the Journal of the American Medical Association that found CTE in 110 of 111 former NFL player brains (99%), and a 2023 update that identified the disease in 345 of 376 donated brains (91.7%). Those findings were significant but carried an inherent limitation: selection bias. Families of players who exhibited symptoms during life, such as memory problems, mood changes, or cognitive decline, were more likely to donate their brains for study than families of players who showed no symptoms. The result was a sample that over-represented symptomatic cases and could not establish how common CTE actually was across the full population of former players.
The August 2026 study in The BMJ addressed that limitation directly. Rather than reporting only the rate among donated brains (91.4%, consistent with prior findings), the researchers used the entire population of 878 former NFL player deaths during the 2016-2021 study window as the denominator. Because 215 confirmed CTE cases were identified within a cohort of 878 total deaths, the minimum prevalence rate across the full population is approximately 25%. The true rate is almost certainly higher, since many of the 643 players whose brains were not donated may also have had CTE that was never diagnosed. The 25% figure represents a floor, not a ceiling.
That distinction matters for how the finding is interpreted. Saying that 91% of donated brains had CTE describes the condition among a self-selected group. Saying that at least 25% of all former NFL players who died in a given period had confirmed CTE describes the condition at the population level. The first number is about severity within a sample. The second is about how widespread the disease is across the entire former player population, regardless of whether symptoms were reported or brains were donated.
The NFLPA Issues a Direct Safety Warning to Active Players
The NFL Players Association responded to the study by issuing an official safety warning to all active roster members, practice squad players, and their agents. The advisory stated that repetitive head impacts, including subconcussive hits that do not result in a formal concussion diagnosis, cumulatively contribute to degenerative brain disease. The warning emphasized that the risk is not limited to players who experience diagnosed concussions during games; it extends to the accumulated effect of routine contact during practices, drills, and plays over the course of a career.
The NFLPA’s decision to communicate the findings directly to players through an official advisory represents a shift in tone from the union’s prior approach, which has historically balanced player safety advocacy with an institutional interest in preserving the sport’s appeal and economic value. By issuing a warning that names CTE explicitly and links it to repetitive impacts rather than only diagnosed concussions, the union is placing the information squarely in front of players at a moment when they can factor it into decisions about their careers, their health management, and their post-football financial planning.
The warning also carries implications for agents, who advise players on career length, contract structure, and disability provisions. If a 25% minimum prevalence rate becomes the accepted baseline for CTE risk among NFL players, agents will need to factor neurological risk into career planning conversations in a way that prior, less precise data did not demand. Insurance products, retirement planning, and post-career support services may all need to be re-evaluated against a risk profile that now has a population-level number attached to it.
What the Study Does and Does Not Prove
The study confirms a causal association between professional football and elevated CTE risk, but it does not resolve several questions that remain open in the scientific literature. The researchers acknowledged that the 25% figure is a minimum bound and that the true prevalence could be substantially higher. Because CTE can only be diagnosed through brain tissue examination after death, there is no way to assess living players for the disease using current technology. That means the study cannot identify which active or retired players currently have CTE, nor can it predict which players will develop it.
The research also does not establish a precise threshold of exposure, in terms of years played, number of impacts, or positions played, that triggers the disease. Previous studies have found CTE in athletes who played only at the high school or college level, suggesting that professional-level exposure is not required. However, the prevalence rates are highest among former NFL players, consistent with the hypothesis that greater cumulative exposure corresponds to greater risk.
The study’s authors noted that the 91.4% rate among donated brains remains subject to selection bias, as it was in prior brain bank studies. Families who donate brains for CTE research are disproportionately those of players who showed symptoms. The 2018 BU study of 164 brains from the general population through the Framingham Heart Study found CTE in only one brain (less than 1%), and that individual was a former college football player. The contrast between the general population rate and the rate among former NFL players underscores the football-specific nature of the risk.
How the NFL Has Responded to CTE Research Over the Past Decade
The NFL’s relationship with CTE research has evolved significantly since the disease first became a major public issue in the mid-2000s. For years, the league disputed the scientific consensus linking football to CTE, funding research through committees that were later criticized for conflicts of interest. The 2015 film “Concussion,” based on the work of neuropathologist Bennet Omalu, brought the issue to a mainstream audience and increased pressure on the league to acknowledge the connection.
Since then, the NFL has made incremental changes to its rules, protocols, and equipment standards. Kickoff rules were modified to reduce high-speed collisions. Practice contact limits were imposed to reduce the total number of hits players absorb during the week. Concussion protocols were formalized, requiring independent medical observers on the sideline and mandating that players who exhibit concussion symptoms be removed from play and cleared by an independent neurological consultant before returning.
The league has also invested in helmet technology, working with manufacturers to develop designs that better absorb and distribute impact forces. The NFL and NFLPA jointly maintain a list of helmets rated by performance in laboratory testing, and the league has banned models that fall below a safety threshold. Equipment improvements, combined with rule changes, have been credited with reducing the incidence of diagnosed concussions during games, though the relationship between diagnosed concussions and long-term CTE risk is not straightforward, since subconcussive impacts that never result in a diagnosis also contribute to the disease.
Despite these measures, the fundamental question persists: can football be made safe enough to prevent CTE, or is the disease an inherent consequence of playing a sport that involves repeated head impacts? The August 2026 study does not answer that question, but by establishing a 25% minimum prevalence rate, it raises the stakes of the debate and provides a data point that future policy discussions, whether at the professional, college, high school, or youth level, will need to confront.
The Timing and What It Means for the 2026 Season
The study’s publication in late August is not incidental. The NFL regular season is set to begin in September, and the weeks before the opener represent the period when national media attention to football safety, player welfare, and the sport’s cultural role is at its annual peak. Training camps are underway. Preseason games have concluded. Roster cuts are being finalized. Players who are weighing whether to continue their careers are making decisions now.
For the league, the study creates a communications challenge at a moment of peak visibility. The NFL has invested heavily in messaging that frames the sport as safer than it has ever been, pointing to rule changes, protocol improvements, and reduced concussion counts as evidence of progress. A headline finding that one in four former players had a degenerative brain disease cuts against that narrative, even if the study period (2016-2021) reflects conditions that may have since improved.
For parents, coaches, and administrators at the youth and high school level, the study adds weight to a decision that millions of American families make every fall: whether to allow their children to play football. Youth football participation has declined in recent years, partly in response to CTE research, and a population-level prevalence rate may accelerate that trend. The study does not directly address youth football, but the researchers have noted in prior work that CTE has been found in athletes whose exposure was limited to high school and college play, meaning the risk is not confined to professionals.
For active players, the NFLPA’s safety warning places the 25% figure in a context that is immediately personal. A player entering the 2026 season now has access to data suggesting that at minimum, one in four of his predecessors who have died in recent years had a brain disease that eroded their cognitive function before it ended their lives. What each player does with that information, whether it changes how they approach their career, their contract negotiations, their post-football planning, or their daily decisions about practice intensity, remains individual. But the information itself is no longer ambiguous.
FAQs
What Did the August 2026 CTE Study Find?
The study, published in The BMJ on August 25, 2026, found that at least 25% of 878 former NFL players who died between 2016 and 2021 had confirmed CTE. Among the 235 brains donated for analysis, 215 (91.4%) showed CTE pathology. The 25% figure represents a minimum population-level prevalence rate.
Who Conducted the Study?
The research was conducted by Harvard University and Boston University in collaboration with Mass General Brigham, building on more than a decade of CTE research at the BU CTE Center.
What Is CTE and How Is It Diagnosed?
Chronic traumatic encephalopathy is a degenerative brain disease caused by repeated head impacts. It is associated with memory loss, cognitive decline, depression, aggression, and progressive dementia. CTE can only be definitively diagnosed through post-mortem examination of brain tissue; there is currently no test for the disease in living individuals.
How Did the NFLPA Respond?
The NFL Players Association issued an official safety warning to all active roster members, practice squad players, and their agents, stating that repetitive head impacts, including subconcussive hits that do not produce a concussion diagnosis, cumulatively contribute to degenerative brain disease.
Does the Study Apply Only to NFL Players?
The study focused on former NFL players, but prior research has found CTE in athletes who played only at the college or high school level. The risk is associated with cumulative exposure to repetitive head impacts, not exclusively with professional-level play.
