At least one in four former NFL players who died between 2016 and 2021 had chronic traumatic encephalopathy, the degenerative brain disease linked to repeated head hits, according to a new study published Tuesday in The BMJ that researchers call the most rigorous prevalence estimate yet produced.

The team, led by researchers at Mass General Brigham and the Boston University CTE Center and the Concussion & CTE Foundation, identified 1,712 former NFL players who died between 2008 and 2021, then focused on the 2016-2021 window, when brain-donation rates were highest. Of 338 players whose families donated brains to BU's UNITE Brain Bank during that stretch, 315 — 93.2% — were diagnosed with CTE.

Because donor families are more likely to come forward when a player showed symptoms, researchers built a statistical range to account for players whose brains were never examined. That produced an estimate that somewhere between 24.5% and 97.7% of all deceased players in the group had the disease. CTE affects less than 1% of the general population, the researchers noted.

The findings went beyond diagnosis alone: 61.3% of brain donors found to have CTE also met clinical criteria for dementia, and more than 90% of those with the most advanced form of the disease, stage IV, had been diagnosed with dementia before death.

"A wake-up call"

"To find that somewhere between 24.5% and 97.7% of NFL players ... had this progressive brain disease is a wake-up call."

That's according to Dr. Daniel Daneshvar, the study's lead author and chair of physical medicine and rehabilitation at Mass General Brigham, per NPR. Jesse Mez, co-director of clinical research at the BU CTE Center, said the numbers demand 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."

CTE can currently be diagnosed only after death, through autopsy of brain tissue, which is why researchers rely on donation programs like BU's rather than screening living players. Earlier research on tens of thousands of NFL alumni had already found elevated death rates from ALS, dementia and Parkinson's disease among the group.

The NFL, in a statement reported by CBS News, said the league "continuously strives to make the game of football safer, including by implementing strategies to reduce concussions and head impacts," pointing to rule and equipment changes adopted in recent years. The league has previously acknowledged a link between football and CTE without endorsing specific prevalence figures.

The study was funded in part by the National Institute of Neurological Disorders and Stroke and the National Institute on Aging. Researchers said the wide uncertainty range underscores the need for a way to diagnose CTE in living players, work some of the same labs are already pursuing. For now, the findings add fresh pressure on the league over player safety just as the 2026 season kicks off, with former-player advocacy groups expected to renew calls for expanded health monitoring and benefits for retirees.