High impact sports such as American football, ice hockey and rugby are starting to lead to problems later in life usually associated with former boxers, Dr Willie Stewart said.
In an interview with BBC Radio Scotland the neurologist discussed his research of the brain with a former rugby player where he examined sections of tissue and found abnormal proteins associated with head injuries and dementia.
The former player who took part in the study was found to have higher levels of the protein than a retired amateur boxer who has dementia pugilistica, also known as punch drunk syndrome.
Symptoms usually appear around 15 years after the boxer’s career begins and include memory, speech and personality problems and a lack of coordination.
Until recently it had been thought to only affect boxers who suffered repeated concussive injuries through blows to the head, Dr Stewart said.
The percentage of rugby players affected is likely to be lower than other high impact sports where concussion is common, but it remains a concern.
Speaking on BBC Radio Scotland’s Sport Nation programme, Dr Stewart said: “What we’re find with people who’ve survived head injuries is that their brain shows changes down the microscope that look very much like what you would see in people with dementia, so similar abnormalities in people with Alzheimer’s Disease.
“Now, we’ve known that in boxing for instance repeatedly injuring your brain can read to a syndrome, punch drunk syndrome, and you can imagine what that is.
“The pathology of that is better classified as dementia pugilistica and we kind of assumed it was only boxing related and you had to be exposed to a lot of concussive injuries. But what we’re seeing here and in America is that it’s happening in other sports where athletes are exposed to head injury in high levels.
“Those sports include American football, ice hockey and now I’ve seen a case in a person whose exposure was rugby.
“The damage is a number of things, we see a build up of a protein on the brain that normally appears in Alzheimer’s cases, it builds up in nerve cells and is associated with the brain not working properly, so causes memory problems and personality problems.”
Dr Stewart, who is based at the Southern General Hospital in Glasgow, believes better precautions have to be taken by players and organisers.
“On current evidence from American football and boxing I think it would be foolish to think there will be no problem and that rugby is immune from brain damage,” he said.
“What proportion of players will be affected, how many times you would need to be concussed, how long after will it develop - these are questions we can’t answer but we would suspect it will be a fairly low number but not a zero number.
“If we say it’s 1% of people playing at international rugby level, then in any Six Nations weekend that’s one or two players who could go on to develop a dementia they wouldn’t otherwise have been exposed to.
“The dementia pugilistica stats would say that somewhere between 15% and 20% of boxers who retire after a long career will develop the dementia. I don’t believe rugby is anywhere near that category, but even if its only 1% that’s a concern.”
The neurologist said all sports that carried the risk of head injury, including football, horse racing and show jumping, had a responsibility to ensure athletes recover fully.
“The general advice for concussion is ‘if in doubt sit it out’.
“So for all levels of sport if you think there has been a concussion the player should be removed and not exposed to risk, because the second head injury coming in a short space of time before the brain has properly recovered can be much more severe.”