Rugby must now take "rapid action" after a landmark Scottish study found former international players were 15 times more likely to develop Motor Neurone Disease (MND).

Professor Willie Stewart, the consultant neuropathologist who led the research, said the results were "surprising" and suggested there could be grounds for a review of match frequency to limit head impact.

The health outcomes of 412 male ex-players were compared with 1200 matched individuals in the general population.

The risk of dementia was more than doubled in rugby players, roughly the same as previously observed among footballers by the University of Glasgow team. They also had a three-fold risk of Parkinsons Disease.

While soccer players and American footballers are known to have increased risk of MND Prof Stewart said it was, "nothing like the risk seen in rugby players".

Scottish former rugby union player Doddie Weir and England's Rob Burrow are among the high-profile rugby players to have contracted MND, which affects nerves in the brain and spinal cord and is a severely life shortening condition. 

Prof Stewart said it was possible that the results could have thrown up a chance cluster of MND but added: "It is significantly concerning that we need to roll up our sleeves and find out why it is happening.

"This has come as a big surprise to us to see this figure. 

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"What we  need to do now is take a step back and gather round us some really smart people who work in this field regularly and really focus our attentions on it as quickly as possible to understand what is going on here.

"If this is a more widespread problem in rugby then we really need to do something about it pretty quick."

MND Scotland has been asked to convene an expert group, in light of the study's results, to provide advice to Scottish Rugby on how screening could be developed and built into health checks for current and former players.

READ MORE: Footballers facing 'phenomenal risk' says Glasgow brain injury expert 

In recent years post mortem studies of brain tissue have uncovered evidence of neurological disease uniquely associated with a previous history of traumatic brain injury or repetitive head impact exposure—termed chronic traumatic encephalopathy neuropathologic change (CTE-NC).

It has been found in former professional athletes from sports including American football, soccer, and rugby union.

The research did not specify how many rugby players developed MND due to the risk of identification but Prof Stewart said it was "significantly more than one." No cases were identified in the control group.

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While rugby players tended to live longer than the general population (79 compared with 76), the risk of dying from cancers and cardiovascular disease was not lessened by the sport, unlike in football, although they were less likely to suffer respiratory illnesses.

Researchers say this suggests "sport-specific" factors may be a play in rugby.

READ MORE: Dementia risk five times higher for football defenders 

Their risk of brain diseases was also not influenced by player position, again unlike football where defenders were found to be most at risk and was linked to frequency of headers.

"Rugby has talked a lot about head injury management [but] I think those conversations have gone on a while and progress is pretty slow," said Prof Stewart.

"I think this should be a stimulus for them to pick up their heels and start making pretty dramatic changes as quickly as possible to try to reduce risk.

"Instead of talking about extending seasons and introducing  new competitions they should maybe talk about restricting it as much as possible, cutting back on the amount of rugby we are seeing and restricting training.

"I think they need to look at the number of matches being played and ask is this credible that young men and women are playing week in and week out the majority of the year just for entertainment and is there a way we can trim that back."

READ MORE: Scotland icon Denis Law reveals 'mixed dementia' diagnosis in emotional statement 

The research is part of the FIELD study, which has previously found footballers have a five-fold risk of Alzheimer's Disease. 

While is is the largest study to date looking at the risk of neurodegenerative conditions in rugby, Prof Stewart said it was still "quite small" and more research is urgently required involving thousands of former players including women.

Of the former players who took part around 100 have since died, a similar number to the general population. All were aged 30 years or over at the end of 2020. 

He said the study was largely covering athletes involved in the amateur era of the sport when many players had other jobs.

He said: "This would be things like farming and agricultural work and we know that some of the chemicals involved are also known as a risk factor for MND and so that might be combining with what we are seeing."

His advice to parents who are concerned about sending their children to rugby training is to ask club coaches if they are aware of head injury protocols and if not, "walk away."

Scottish Rugby’s Chief Medical Officer, Dr James Robson, said: “We welcome today’s study and all investigations into this important area to better understand the issues raised and continually improve our approach to player welfare.

“Work continues in Scotland, on and off the field, to address player safety, taking the issues involved seriously.

“We have a proactive approach demonstrated through the newly established Brain Health Clinic, set up by Scottish Rugby, and by partnering with organisations such as HITIQ to improve our understanding of concussion and contact in rugby through head impact sensor technology in mouthguards, alongside partnering in a number of other research projects.”

 “Rugby continues to have many health and social benefits. Important research like this can help us continue to improve safety and mitigate risks associated with contact sport.”

Dr Jane Haley, Director of Research at MND Scotland, said: “While the initial results do seem concerning, the study is based on a small sample size which means that, because MND is a relatively uncommon condition, larger studies will be needed to determine whether this result can be confirmed more widely.

“A connection between elite level sports and MND has been proposed before, but this is the first time an increased risk has been indicated for rugby players.

“Following these results MND Scotland will be working closely with Prof Stewart, Scottish Rugby and the Brain Health Clinic in Murrayfield, to form an advisory group of MND professionals.”

A new BBC documentary focussed on English former rugby union player Steve Thompson will be screened on Wednesday. The 44-year-old was diagnosed with early onset dementia in 2020.