The risk of a degenerative brain disease increased by 14% with every year of rugby play in both elites and amateurs, a  Glasgow-led study has found.

Researchers studied the postmortem results of 31 former amateur and rugby union players whose brains were donated for medical science.

Chronic traumatic encephalopathy (CTE) was found in around two-thirds (68%) of the brains examined, and in both amateur and elite players.

CTE is a degenerative brain condition linked to dementia that has been shown to be, at least in part, a result of exposure to repeated head impacts and head injuries.

The risk increased by 14% with every year of rugby play. Player position or level of participation, either amateur or elite, did not appear to influence risk.

The average rugby career length was around 18 years, with an equal number of forward and backs.

Twenty-three (74%) played rugby exclusively as amateurs, with 8 (26%) reaching elite level, either as professional or representative internationalists.. 

READ MORE: Rugby's Dan Scarbrough says the sport caused illness 

Over the past decade or so, there has been increasing evidence of a link between CTE and contact sports including football, American football, boxing and rugby.

To date, the only recognised risk factor for CTE is traumatic brain injury and repeated head impact exposure.

Rugby union is known to have a high risk of mild traumatic brain injury (concussion), with injury rates highest in the professional game.  

The study was led by Professor Willie Stewart at the University of Glasgow and follows major findings from his group last year which found former professional players were more than three times more likely to develop Parkinson's, and over 15 times more likely to develop Motor Neurone Disease (MND).

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He also led research showing ex-footballers had a three-fold risk of neurodegeneratie diseases including dementia and were five times more likely to develop Alzheimer's Disease. In this case player position was linked to risk with defenders - who are most likely to head footballs - five times more likely to be affected.

READ MORE: Motor Neurone Disease rugby link 'significant' finds Glasgow study 

Professor Stewart said:  “These results provide new evidence regarding the association between rugby union participation and CTE.

"Specifically, our data show risk is linked to length of rugby career, with every extra year of play increasing risk.

"Based on this it is imperative that the sport's regulators reduce exposure to repeated head impacts in match play and in training to reduce risk of this otherwise preventable contact sport-related neurodegenerative disease.”

The number of rugby players suing the game's authorities over head injuries is set to increase to nearly 300.

The claims against the Welsh Rugby Union, Rugby Football Union and World Rugby are that players sustained brain damage through playing the sport.

READ MORE: Fund for ex-players with dementia launched by PFA and Premier League

Prof Stewart said he believed the current form of rugby union as it is played would change straight after the World Cup.

World Rugby said the sport was at the forefront of preventing, managing and identifying head impacts and wanted to make the sport as safe as possible for everyone.

It is to introduce smart mouthguard technology that can send pitchside alerts if a player has experienced a high level of acceleration which could lead to an injury.

The measure follows peer-reviewed research in ice hockey that found that "as well as protecting against dental injuries, mouthguards can reduce the risk of a concussion by 20 per cent".

A spokesman said: "World Rugby will never stand still when it comes to protecting players’ brain health which is why community players around the globe are taking part in trials of a lower tackle height this season."

Scottish Rugby’s Chief Medical Officer, Dr James Robson added: “We have been doing work for many years on player welfare and taken practical steps this season to make the community game safer by lowering the tackle height to reduce the risk to players and combined this with launch of a new online concussion education course, digital concussion hub and Player Welfare Action Plan for coaches, players and parents to access to ensure we all focus on enjoying rugby safely.”

The latest findings are a world-first collaboration with Boston University and the University of Sydney.

Ann McKee, MD, director of Boston University CTE Center and co-author of the study, said: “CTE is a preventable disease; there is an urgent need to reduce not only the number of head impacts, but the strength of those impacts, in rugby as well as the other contact sports, in order to protect and prevent CTE in these players.”

The paper, ‘Risk of chronic traumatic encephalopathy in rugby union is associated with length of playing career’ is published in Acta Neuropathologica.