A new study released on Wednesday estimates that about 75% of former NFL players who died over a 15-year span had signs of chronic traumatic encephalopathy, the degenerative brain disease known as CTE.
The research appeared in Jama Network Open and was carried out by a team based in Boston. It looked at players who died between 2008 and 2023 and found that the estimated rate of CTE in this group was far higher than the rates seen in brain samples from the general population.
The analysis drew on records for 2,362 deceased former NFL players, who spent an average of five years in the league. Close to 400 of them had their brains donated for examination, and 93.5% of those donated brains showed evidence of CTE.
According to the researchers, this is the first attempt to estimate how common CTE was among all former NFL players who died in that period, rather than only among those whose brains were donated for study.
The gap with the wider population is large. The authors said that fewer than 1% of brain samples held by community-based brain banks contain evidence of CTE. Physical hallmarks of the condition include brain atrophy, meaning a loss of brain tissue, and buildups of tau protein, which is also linked to Alzheimer's disease.
The study also stressed limits on what the findings mean. Having CTE-related changes in the brain does not automatically lead to dementia or a decline in thinking skills, and some people with the condition never develop noticeable symptoms. The researchers estimated that around 27% of the former players in the analysis had dementia. CTE can also affect parts of the brain that govern emotional control and behavior, with possible symptoms including depression, memory problems and severe mood changes.
Yorghos Tripodis, the study's senior author, acknowledged the potential for worry in a statement issued by Mass General Brigham. "We recognize these findings may cause concern for the community of living players and their families," he said, adding that researchers and others are "standing by to provide support" and that there is hope for people living with CTE.
Tripodis said discoveries from the brain bank have already brought researchers "significantly closer to a diagnosis during life," at which point the most important goal will be developing effective treatments.
The results follow another study released in August, which found that at least one in four former NFL players who died between 2016 and 2021 had CTE. After that earlier report, the NFL said it "continuously strives to make the game of football safer, including by implementing strategies to reduce concussions and head impacts."
Several high-profile former players who took their own lives, including Junior Seau, Dave Duerson and Aaron Hernandez, were found to have had CTE when their brains were examined after death.
