At least one in four NFL players who died between 2016 and 2021 had the degenerative brain disease known as CTE, a new study has revealed. The study, published Tuesday by the British Medical Journal, focused on how common chronic traumatic encephalopathy might be among NFL players. What it found is that of the 878 players who appeared in at least one NFL game and died in that six-year period, at least 25% had CTE.

CTE can be diagnosed only after death, so most research has depended on brains donated by players or their families. This study drew on samples donated between 2008 and 2021, 93% of which had been diagnosed with CTE, then narrowed the sample based on when donations were highest and factored in demographic data and information from death certificates. The estimate of 25% is on the "low end," said Dr. Daniel Daneshvar, the study's lead author. The study found that the maximum possible prevalence of CTE was around 97%, but the true rate "is somewhere in the middle," Daneshvar said.

"This study is a sobering reminder that football carries real risks, and those risks can have lasting consequences for players and their families," the NFLPA said in a statement to ESPN. "It also reinforces one of the NFLPA's core priorities: improving player safety and supporting players throughout their lives, both during and after their careers." The findings should serve as a call to action across the entire football ecosystem.

The NFL "continuously strives to make the game of football safer, including by implementing strategies to reduce concussions and head impacts," the league said in a statement. The study also looked at the link between CTE and dementia, finding that more than 90% of samples of the most advanced stage of CTE, Stage 4, were also diagnosed with dementia. Daneshvar noted that since the biggest predictor of CTE is the cumulative force of hits to the head, that risk can be mitigated by things such as eliminating hits during practices and having children not play tackle football.