LONDON (Dispatches) - A study of American football players' brains has found that 99% of professional NFL athletes tested had a disease associated with head injuries.
The report published on Tuesday in the Journal of the American Medical Association studied 202 deceased players - 111 of them from the NFL.
All but one former National Football League player were found to have chronic traumatic encephalopathy (CTE).
The study is the largest of its kind yet conducted, its authors say.
Dr Ann McKee, director of Boston University's CTE Center, which led the study, cautioned against drawing any immediate conclusions.
"There's a tremendous selection bias," she said, explaining how many of the brains were donated specifically by families who had suspected that their loved ones were suffering from CTE, which researchers believe is caused by repeated blows to the head.
The neurodegenerative brain disease CTE is typically found in people who have suffered repeated blows to the head, studies have found.
All 202 players studied - ranging in age from 23 to 89 - were required to have football as their primary exposure to head trauma.
Of the 202 total players, 87% were found to have traces of CTE.
It was also found in 48 of 53 college players and three of the 14 high school players.
Players featured in the study came from every position on the field, and from high school, university, and Canadian leagues, in addition to the NFL.
****The donated brains of college and high school players were also studied.