WASHINGTON (Deutsche Presse-Agentur (dpa)) -- A new study suggests that mild but repeated brain injuries often sustained by athletes can lead to degenerative brain disease in the long run.

The study, published Monday in the neurology journal Brain, found that 80 per cent of 85 brains analyzed posthumously, all from patients who had histories of mild traumatic brain injury, showed signs of chronic traumatic encephalopathy (CTE).

CTE is a degenerative brain disease caused by repeated blows to the head, leading to memory loss, depression and dementia, which are symptoms often experienced by American football and ice hockey players and other contact-sport competitors.

Out of the 68 individuals in the small study with signs of CTE, almost all the subjects were professionals or high-level amateurs in football, ice hockey, boxing or wrestling.

Head injuries in football, especially among professionals in the National Football League, have been a recurring issue in recent years after several high-profile suicides of retired players who were Described as suffering depression, which is a symptom of CTE.

In May, only two years after his retirement, long-time San Diego Chargers linebacker Junior Seau, 43, shot himself in the chest. A likely future Pro Football Hall of Fame inductee, his his suicide and depression were linked to brain damage, despite being outwardly lucid and cheerful during and after his playing career.

In April, Ray Easterling, 62, a safety for the Atlanta Falcons, shot himself after a 20-year battle with depression.

The NFL was reeling this week from the even more stunning demise of Jovan Belcher, a linebacker for the Kansas City Chiefs, who police say shot and killed his girlfriend on Saturday before going to the team's training centre and shooting himself in the head, in front the head coach.

Belcher and his girlfriend, Kasandra Perkins, with whom he had a now-orphaned 3-month-old daughter, were having relationship issues and attended counseling, according to the Kansas City Star.

"This wasn't forthcoming of his character," said former college teammate Raibonne Charles. "Jovan is a very passionate, very emotional person, and you could tell that by watching him play the game. But this is a shock to us all."

Belcher's death is still under investigation.

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