As a new American football season is set to begin, researchers examining the brains of deceased NFL players have found that 99 percent of them showed signs of degenerative disease -- believed to be caused by repeated blows to the head.

Researchers found striking evidence of chronic traumatic encephalopathy in 110 of the 111 donated brains of players who played in the National Football League, according to the study published Tuesday in the Journal of the American Medical Association.

CTE causes symptoms including memory loss, vertigo, depression and dementia. Problems can crop up years after a player's career has ended.

The NFL has faced growing scrutiny in recent years linked to the issue of concussions and head trauma, with the league agreeing in 2015 on a $1 billion settlement to resolve thousands of lawsuits by former players suffering from neurological problems.

Along with NFL players, researchers also examined the brains of those who had played in high school, college, semi-professionally and in the Canadian Football League.

Of the total 202 players examined, the authors of the study from Boston University found that 87 percent of the players -- whose median age at death was 66 years old -- showed signs of CTE.

The most acute evidence of the degenerative condition, which currently can only be diagnosed post-mortem, was found among those who played at the highest levels, with 86 percent of professional players having severe forms of CTE.

Though the research -- the largest CTE study published to date -- suggests the disease may be related to prior participation in football, researchers cautioned against extrapolating the results to the general population.

Because the brains studied were for the most part donated by concerned families, they do not necessarily represent all people who have played the rough contact sport.

Last year, an NFL official acknowledged for the first time a clear link between football and CTE.

In recent years, the league has donated money to concussion research and stepped up regulations in an attempt at minimizing the potentially traumatic physical impact of the game.

source: AFP