New model estimates 75% CTE rate in dead NFL players

Boston University researchers estimate that 75% of former NFL players who died between 2008 and 2023 had chronic traumatic encephalopathy, or CTE.

The study, published Wednesday in JAMA Network Open, presents the highest prevalence rate reported to date. This figure is three times higher than a previous estimate from the same group, which found that one-quarter of players who died over a five-year span had the condition. The new analysis also suggests that approximately 27% of the deceased former players had dementia.

Yorghos Tripodis, director of statistics and data management at the Boston University Alzheimer's Disease and CTE Center, stated that the high number required verification. He noted that the figure is an estimate because CTE cannot currently be diagnosed in living patients. The center operates the UNITE Brain Bank, which examines donated brains for signs of repetitive head trauma.

The research team faced a challenge because CTE is only detectable through microscopic analysis at autopsy. Previous studies have been criticized for selection bias, as families of players with cognitive symptoms are more likely to donate brains. To address this, Tripodis and colleagues combined data from 396 donated brains with national death records for 1,966 other deceased players.

The team factored in the players' ages at death and estimated rates of mild cognitive impairment and dementia among former players over 50. Analysis showed that about 93% of the donated brains contained signs of CTE. The researchers calculated that families of symptomatic players were five times more likely to donate brains. They applied a statistical correction to account for this disparity, estimating that 1,760 of the 2,360 players who died during the study period had the disease.

Experts outside the study urged caution regarding the findings. Jim Kelly, a professor emeritus of neurology at the University of Colorado Anschutz, pointed out that the team did not have autopsies for five times as many players as they did. He observed that some autopsies may have revealed only minor lesions, which might not lead to behavioral changes or dementia. For context, the researchers noted that only about 1% of brains donated to banks in the United States, Austria, and Brazil show signs of the disease.

Julian Bailes, chair of neurosurgery at Endeavor Health, explained that repeated head impacts cause tau proteins to accumulate in the brain. This accumulation can affect areas governing behavior and emotion, leading to memory loss and mood swings. He emphasized the need for better diagnostic tools for living people. In response to the findings, an NFL spokesperson said the league continues to implement strategies to reduce concussions and head impacts, including the use of the Guardian Cap and the dynamic kickoff rule.