Boston University study estimates CTE in nearly 75% of deceased former NFL players

A Boston University-led study published on October 28 estimates that 74.5% of former NFL players who died from 2008 to 2023 had chronic traumatic encephalopathy, or CTE. CBS News reported the finding, which adjusts for the greater likelihood that players with cognitive symptoms would have their brains donated for study. It does not establish how common CTE is among living players.

The estimate is substantially lower than the rate observed in donated brains. CBS News reported that researchers found CTE in 362 of 387 deceased former players whose brains they examined, about 94%. They estimated that players with cognitive symptoms were five times as likely to have their brains donated, then used that estimated difference to arrive at the 74.5% figure.

How researchers adjusted the CTE estimate

Brain donation poses a problem for estimates of CTE because players with cognitive decline, or their families, may be more likely to seek an autopsy or donate a brain, NBC News reported. CBS News said an earlier study by the same researchers put the estimated rate among former NFL players who died from 2016 to 2021 anywhere from 25% to 98%. That wide range reflected uncertainty about how representative the donated brains were.

What the finding means for living players

CTE can be definitively diagnosed only after death, NBC News reported. The new estimate concerns players who have died and cannot be used to calculate how many living former or active players have the condition. Brain changes associated with CTE also do not mean that a person necessarily experienced symptoms, cognitive decline or dementia.

The researchers estimated that 27% of the players studied had dementia, NBC News reported. A study leader said that figure included dementia from all causes. Dr. Jim Kelly, a University of Colorado Anschutz neurologist who was not involved in the research, cautioned that the CTE figures remain estimates because far more players in the group had no autopsy. He also said limited lesions found in some autopsies might not lead to behavioral change or dementia.

In a statement reported by CBS News, the NFL said it was working to reduce concussions and head impacts, pointing to equipment such as Guardian Caps and changes to playing rules. The NFL Players Association called research into football’s long-term health effects critical and said it supported research and access to care for players.