A new analysis in the Journal of the American Medical Association estimates that roughly three in four former National Football League players who died between 2008 and 2023 had chronic traumatic encephalopathy (CTE), the degenerative brain disease linked to repeated head impacts.

The study looked at 2,362 deceased former players. Of those, 396 donated their brains, and 93.5% of the donors had CTE. Because CTE can be diagnosed only after death, and families who noticed cognitive symptoms are more likely to donate, the researchers estimated such families were about five times more likely to donate and adjusted for it. After the adjustment, they estimated that 74.5% of the former players had CTE, ABC News reported. They also estimated that 27.2% had dementia during their lifetime, about one in four.

Yorghos Tripodis, a biostatistics professor at Boston University and the one author named in the coverage, said: “even under very conservative assumptions, the estimate does not go below 60%.” An earlier study by many of the same researchers, published in August, found that at least one in four former players who died from 2016 to 2021 may have had CTE, with a range of 25% to 98%. “We wanted a more precise answer,” Tripodis said.

The league and the players’ union responded in different tones. The NFL Players Association said: “Studies like this are critical to improving our understanding of football’s long-term impacts.” The NFL said it “continuously strives to make the game of football safer,” pointing to strategies for reducing concussions and head impacts and to resources for players’ physical and mental well-being.

The findings carry limits. They apply to deceased former players and may not represent those playing now. The adjustment for brain donation corrects a known bias, but ABC notes that no study can remove every possible bias, and the researchers say the dementia estimate probably understates how common dementia is. The coverage does not report a confidence interval.

The result lands in a wider debate on contact sport and brain health, including research into whether CTE can be treated or prevented. For parents, coaches and school boards in India weighing contact-sport programmes, the study speaks to elite American football players, not to amateur play, and does not by itself measure risk at lower levels of exposure.