About three in four former NFL players who died between 2008 and 2023 had chronic traumatic encephalopathy, or CTE, a new Boston University study estimates. CBS News and NBC News report the study was published Wednesday in JAMA Network Open.

CTE is a brain disease linked to repeated blows to the head. It can lead to memory loss, depression and mood swings. It can only be confirmed by an autopsy after death.

NBC News calls it the highest estimate to date. A study in August by the same group put the share at about one quarter for players who died over a five-year span, NBC reports.

Past studies drew criticism because families of players with symptoms are more likely to donate brains. The team found those families were about five times as likely to donate. They then adjusted for that bias using national death records, the outlets report.

NBC News reports the team estimated that about 1,760 of roughly 2,360 former players who died in the period had CTE. About 27 percent had dementia. By contrast, the disease shows up in about 1 percent of brains given to community brain banks.

"I had to double-check the numbers," study leader Yorghos Tripodis said, according to NBC News. Lead author Julia Gallini said the finding "suggests we need to increase efforts to support families, diagnose CTE during life, and treat CTE-related symptoms."

Outside experts noted limits. "These are all estimates," said Jim Kelly, a neurologist at the University of Colorado Anschutz.

The NFL said it "continuously strives to make the game of football safer," pointing to Guardian Caps and rule changes. The players union called such research "critical." Patriots coach Mike Vrabel, a former linebacker, said players "knew what the risks were."

What we know: A Boston University study estimates about 75 percent of NFL players who died over the period had CTE.
What we don't: How many living former or current players may have the disease.