According to a study on 202 deceased athletes, almost all American football players, including the professionals in the US National Football League have suffered from a brain disease which is linked to continuous head injuries.
Chronic traumatic encephalopathy (CTE) is a progressive neurodegeneration associated with repetitive head trauma.
American football players may be at an increased risk of long-term neurological conditions, particularly CTE, according to the study.
Researchers from Boston University in the US examined the brains of 202 deceased former football players to determine neuropathological features of CTE through laboratory examinations.
They analysed the clinical symptoms of CTE by talking to players next of kin to collect detailed histories including on head trauma, athletic participation and military service.
Researchers found that among the 202 football players (median age at death was 66), CTE was neuropathologically diagnosed in 177 players (87 per cent) who had had an average of 15 years of football participation.
The 177 players included three of 14 high school players (21 per cent), 48 of 53 college players (91 per cent), nine of 14 semi professional players (64 per cent), seven of eight Canadian Football League players (88 per cent), and 110 of 111 NFL players (99 per cent), researchers said.
Neuropathological severity of CTE was distributed across the highest level of play, with all three former high school players having mild pathology and the majority of former college (56 per cent), semi-professional (56 per cent), and professional (86 per cent) players having severe pathology.
Researcher noted that among 27 participants with mild CTE pathology, 96 per cent had behavioural or mood symptoms or both, 85 per cent had cognitive symptoms, and 33 per cent had signs of dementia.
Among 84 participants with severe CTE pathology, 89 per cent had behavioural or mood symptoms or both, 95 per cent had cognitive symptoms, and 85 per cent had signs of dementia.
"In a convenience sample of deceased football players who donated their brains for research, a high proportion had neuropathological evidence of CTE, suggesting that CTE may be related to prior participation in football," researchers said.
They acknowledged that several other football-related factors may influence CTE risk and disease severity, including but not limited to age at first exposure to football, duration of play, player position and cumulative hits.
The study was published in The Journal of the American Medical Association.