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While top UK neurologists and other medical experts are increasingly seeing persuasive signs of a link between rugby and dementia, one former Lion has no doubt the connection is real.
Former Scotland No8 John Beattie has been documenting the struggles of a number of former rugby players for the BBC.
"I'm completely convinced that if you keep bashing your head in rugby, you'll end up with a brain injury like early onset dementia," he told the New Zealand Herald from his Scotland home.
Following a documentary he made for the corporation, Beattie was contacted by a number of former players who he described as having "terrible problems". The age of these players who were having cognitive troubles such as memory loss was the most frightening aspect.
"Some of them were barely 40," Beattie said.
Beattie helps with a programme called Rugby Memories, which aims to counter the effects of dementia by stimulating memories of great moments in the game. In one session he met former Scotland wing Dave Shedden, who had Alzheimer's in his early 50s.
His daughter Lynne told Beattie she recounted 13 times when her father was concussed playing rugby, including three times on one tour.
Shedden, known as The Spear because of his tackling style, was knocked out against Wales at Cardiff Park one afternoon. He was not allowed to use the hotel phone to tell his family he was safe, but instead had to walk outside to find a pay phone.
Beattie talked to former Scotland Rugby Union doctor Donald MacLeod, who confessed to fearing for the futures of many players.
"I always worry whether someone who's not 100% equivalent to their peers, irrespective of their age, is it because they got lots of head knocks while playing rugby," Dr MacLeod tells Beattie.
"I think about it almost every Saturday when I go watch a game somewhere ... and I hear about people who are not coming to games because they're not fine."
Willie Stewart, a neurologist who Beattie says is "100% convinced sub-concussive impacts cause brain damage", was the first to conclusively find evidence of what is now known as Chronic Traumatic Encephalopathy (CTE) in an autopsy of a deceased rugby player.
The neurologist told the BBC: "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."
There has been high-profile criticism of rugby's attitude to concussion in the UK. The most prominent dissenter was Barry O'Driscoll, uncle of legendary Ireland and Lions centre Brian, who resigned from his position on the International Rugby Board's medical advisory panel in protest at its handling of head injuries.
He said authorities were "playing Russian roulette" with players' health.
Dr Stewart said there was no way of knowing how many times a player would need to be concussed to be affected, how long after their careers it would develop, or how many players would be affected.
"If we say it's 1 per cent of people playing at international level, then in any Six Nations weekend that's one or two players who could go on to develop dementia they wouldn't otherwise have been exposed to ... even if it's only 1%, that's a concern."