Defenders are more likely to have dementia in later life compared with other playing positions in football, says new research.
In 2019, a study by Professor Willie Stewart found that former footballers were about three and a half times more likely to die of neurodegenerative brain disease than the general population.
But his new research says the risk is highest among defenders, who are five times more likely to have dementia than non-footballers.
That compared with three times the risk for forwards, and almost no extra risk for goalkeepers compared with the population.
Outfield players were four times more likely to have brain disease such as dementia.
The research by the University of Glasgow, which was funded by the Football Association and players' union the Professional Footballers' Association, also found that risk increased the longer a player's football career was.
And despite changes in football technology and head-injury management in recent years, there was no evidence that neurodegenerative disease risk changed for footballers in this study, whose careers spanned from about 1930 to the late 1990s.
'Footballs should be sold with a health warning about heading'
Study author and consultant neuropathologist Dr Stewart said that it was time for football to eliminate the risk of heading, which he said could also cause short-term impairment of brain function.
"I think footballs should be sold with a health warning saying repeated heading in football may lead to increased risks of dementia," he said.
"Unlike other dementias and degenerative diseases, where we have no idea what causes them, we know the risk factor [with football] and it's entirely preventable.
"We can stop this now and to do that we have to reduce, if not eliminate, unnecessary head impacts. Is heading absolutely necessary for football to continue? Or to put it another way: is exposure to the risk of dementia necessary for football?
"I've yet to see any evidence that heading a ball is good for you. Football is great for you, there is less cancer and cardiovascular problems for players, but there are dreadful levels of dementia and I can't see the benefit of that."
New heading guidance 'unscientific guesswork'
The research comes a week after English football published recommended limits on heading for professional and amateur players in training. It follows previous restrictions across England, Scotland, Wales and Northern Ireland for heading in youth teams.
From next season professional players will be limited to 10 'higher-force' headers in training from long passes, corners or free-kicks, whereas in the amateur game players should be limited to 10 headers per week.
But Stewart was critical of those guidelines saying they were based on "unscientific guesswork" and cited the Scottish Football Association, who waited for the latest FIELD (Football's Influence on Lifelong Health and Dementia Risk) study before publishing its heading advice.
He added: "There is no basis to say 10 headers of a certain level will necessarily make a great difference to the risk. The FA based their recommendations on analysis of matches, estimated what the forces might be and then used that for training guidance.
"That's like being stood on the edge of the motorway and guessing cars' speeds and talking about road traffic measures in a city. It's not entirely relevant.
"To assess whether 10 high-force head impacts might make a difference, we have to wait 30 to 40 years."
The FA said it "welcomed" the new research and said new heading guidelines were supported by research and expertise in the game.
Stewart said that the research, which looked at health records data for about 8,000 Scottish former male professional footballers and matched them against 23,000 men from the general population, put football at the forefront of dementia research in sport.
But he said it was a "global issue" and suggested that it was time for the game to change its formats.
"Maybe professionals with all the support and medical knowledge of the risks can continue to play full-contact heading football," he said.
"But maybe at community and youth level, we can start talking about a game without heading. Do we wait 30 to 40 years? Or do we say the evidence is sufficiently strong where we should consider a sport without unnecessary head impact?
"I think we are well past this point."
Hugh Pym, BBC health editor
Research on head injuries in elite level football and rugby is widening amidst some concerns about longer-term consequences for player health.
The debate has intensified after a long-running campaign by Dawn Astle, whose father Jeff died with dementia after a career involving frequent heading of the ball.
Professor Willie Stewart is one of the leading experts in this area and was commissioned by the Football Association and Professional Footballers' Association in 2017 to carry out research on brain health among players. Two years later his team published preliminary findings on the increased dementia risk amongst former professionals.
This latest study goes much further in identifying defenders and those with the longest careers as being at most risk among players with the conclusion that heading is a key factor.
Professor Stewart is adamant that action is needed now on heading to protect the health of current players. From an expert of his stature and a team funded by the football authorities in England, that amounts to a significant wake-up call for the game.
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