Footballs should carry a health warning, a brain injury expert has suggested, as landmark Scottish research found defenders were five times more likely to develop dementia.

Professor Willie Stewart, the consultant neuropathologist who led the University of Glasgow study, said international governing body FIFA should also consider eliminating headers from the sport, such was the strength of the new data.

The ground-breaking research has already shown that footballers were three-and-a-half times more likely to die of neurodegenerative diseases including dementia and had a five-fold risk of Alzheimer's. However, it did not reach any conclusions as to why this was the case.

Prof Stewart said new data from the same study involving 7676 former professional footballers, playing between around 1930 and 1998, had now provided the "missing link".

It shows that the risk for footballers was dependent on the position played. Goalkeepers had the same risk as the average person while defenders - who head the ball most frequently -  had a five-fold risk and the risk was lowest in forwards (2.79).

The Herald:

The length of time playing was also crucial  - those who played for longer than 15 years were five times more likely to develop brain diseases including dementia.

Prof Stewart said FIFA should now be asking itself some hard questions about the welfare of footballers amid a "dreadful" incidence of dementia amongst professional footballers and suggested football manufacturers should consider warnings on packaging.

Scottish footballers including Celtic's Billy McNeill and Stevie Chalmers are among those who succumbed to the disease. The family of former Scotland and Manchester United defender Gordon McQueen revealed in June that the 68-year-old had been dianosed with dementia.

READ MORE: Billy McNeill Fund to be launched for former footballers affected by dementia

“Unlike other dementias where we have no idea what causes it, we know what the risk factor is here - it is entirely preventable and we can prevent it today," said Prof Stewart.

“I think football has to ask the difficult questions – is heading a ball absolutely necessary to the game of football - after all, it is called football, not head-ball. 

"Is potential exposure to dementia absolutely necessary in playing a game of football or can some other form of game be considered.

"I would actually say that we are at the point now in this current data to suggest that footballs should be sold with a health warning, saying repeated heading of a football can lead to increased risk of dementia.

The Herald:

"That's where we are now, this cannot be ignored. This is what's called good preventable public health. This is a global issue...what is FIFA doing?

"Participation in football is a good thing, there is no question, we see less cardiovascular problems, less cancer but we see dreadful levels of dementia”.

The Herald:

(Former Scotland and Manchester United defender Gordon McQueen, who has been diagnosed with dementia)

The FIELD study (Football’s Influence on Lifelong health and Dementia risk) published two years ago, matched former footballers to 23,028 people who had never played professional football (three per player) taking into account sex, year of birth, socio-economic status and postcode area.

Researchers were looking at the incidence of chronic traumatic encephalopathy (CTE), a degenerative brain disease linked to head trauma and the risk of dementia.

CTE was seen in around three quarters of the brains of former footballers while it was the cause of dementia in around half of the cases.

A total of 386 of the 7676 former footballers and 366 of the 23,028 matched population were found to have neurodegenerative disease. 

Field position data was available for 6622 former players.

Compared with the risk among the general population, the risk among footballers was highest for defenders at 4.98.

Those who had played more than 15 years were more than five times (5.20)more likely to have developed brain disease.

"When we look at goalkeepers where heading is virtually non existent and head injuries are less frequent, we see no measurable risk (of dementia)", said Prof Stewart.

The Herald:

"However, outfield players, we see quite clearly that the risk is higher - about four-fold higher.

"If you are a defender the risk if five times higher."

Played in more than 200 countries and with more than one quarter of a billion active participants, football is the world's most popular participation sport. Prof Stewart said the new data could apply to other sports and wasn't "just a message for football".

READ MORE: Mark Eadie: Is it time to call it a day on heading the ball?

"Football is actually further ahead in terms of understanding what’s happening, than even boxing, than even American football", said Prof Stewart.

“Rugby has different formats. There is the full 15 a side collision sport, it has 7-a-dside where it’s a bit more free-flowing and open and it also has touch rugby where they have taken tackle out  altogether.

“Maybe football needs to consider are there different forms of football we could be looking at.

“Do we wait 30 or 40 years or do we think the evidence is sufficiently strong now.”

READ MORE: Celtic's Lisbon Lion Bertie Auld suffering from dementia, club confirms 

FIFA did not respond to the study's findings when contacted by The Herald.

The research did not provide any evidence that advances in technology over the study period, such as a lighter footballs, had played any role in reducing the risk of dementia but Prof Stewart said it would be 30-40 years before this could be proved conclusively.

He suggested headers could still be included in the professional sport, where players have access to specialist treatment, but it should be removed from the amateur game.

He said that protective headwear, worn in other supports, would not necessarily mitigate the risk and said the treatment of concussion on the pitch including the length of time players were taken out of play was "not where it needed to be". 

The Herald:

(Sir Bobby Charlton was diagnosed with dementia at 83)

He also called for improvements in support for former footballers who have been exposed to brain injury and "haven't yet developed disease".

Responding to the study, Billy McNeill's son Martin, said: "I certainly wouldn't like heading taken out of the game.

"I'd be all for making the game safer and further research into how we can make the game safer. Further support for footballers already diagnosed and earlier intervention for footballers who are yet to be diagnosed."

The Herald:

(Celtic legend Billy McNeill's widow Liz and his son Martin)

In football, concerns about the dementia risk were first highlighted after the death of former West Bromwich Albion player Geoff Astell. Professor Stewart said Astle, who died, aged 59, in 2002, was killed by CTE, caused by heading footballs.

The SFA and the FA introduced a ban on children under 12 heading footballs after the FIELD study was published.

READ MORE: Former Scotland and Manchester United defender Gordon McQueen diagnosed with dementia 

Prof Stewart described plans by the FA to set a limit on the number of 'higher force' headers from free kicks and crosses as ‘unscientific’.

He said: “To know whether this best guestimate 10 high force head impacts might make a difference we would have to wait 30 or 40 years.

"In essence football has to say we accept a risk of dementia for the next 30-40 years to be proven right or wrong rather than football doesn’t accept this and stronger measures have to be taken.”

Jim Pearson, Director of Policy & Practice at Alzheimer Scotland said it was "time to act".

He said: "Football’s governing bodies, players representatives and clubs must now do all they can to protect professional footballers from those risks. That may well mean the game we know and love might need to change."

Dr Christopher Morris, Senior Lecturer in Neurotoxicology, Newcastle University, said "This link to heading a ball, although plausible, isn’t proven and more research will be needed.

"What is unusual in this study is that several different neurodegenerative disorders including dementia, motor neurone disease, and Parkinson’s are linked to professional footballers.

"Normally these different disorders are quite distinct, both in terms of symptoms, but also in the biology that leads to these conditions.

"What might be happening here is that head trauma, in this case very small bumps but many of them, and over a very long period, promotes brain damage in general, leaving a person more susceptible to developing a disorder like Alzheimer’s."

The study, ‘Association of field position and career length with neurodegenerative disease risk in former professional soccer players,’ is published in JAMA Neurology.