Former NRL players who experienced multiple concussions during their careers perform 40 to 50 per cent worse on cognitive testing compared with men who have never had a concussion.
The study of 25 former players was published in the journal Brain Injury last week and reported by The Sydney Morning Herald on Thursday.
"We cannot discount the fact that a history of not just concussion, but head trauma may have effects years later," lead researcher Dr Alan Pearce said.
"It certainly increases the risk of impairment later in life and we need to increase awareness about this issue."
The study found that the former players' reaction times were 15 per cent slower, while they were more than 70 per cent worse at maintaining attention.
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In the US, concussion has become a heated issue in recent years, with NFL players reaching a billion-dollar settlement in a class action against the league.
Closer to home, one of rugby league's original four Immortals, Graeme Langlands, died last month after being diagnosed with dementia while his former St George teammate John Raper is in a nursing home with the same disease.
