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Men who played rugby union at international level are more than twice as likely to develop dementia as the general population.

Previous studies have found that heading the ball in soccer is linked with , and that American football players are more likely than other people to .

at the University of Glasgow in the UK and his colleagues analysed the medical histories and death certificates of 412 male Scottish rugby union players who had all been born between the early 1900s and 1990 and had played the game to an international level. The researchers wanted to determine what effect playing rugby at this level had on neurodegenerative risk.

The rugby players were each matched to three members of the general population by age, sex and socioeconomic status. The researchers gauged a participant鈥檚 socioeconomic status by looking at their last known address. 鈥淟ast known address is a good index of social deprivation,鈥� says Stewart.

By matching rugby players to non-rugby players using these characteristics, the researchers could be more certain that any differences they found in neurodegenerative risk were due to playing rugby.

Through NHS Research Scotland, the team were able to access death certificate and medical prescribing data on the rugby players and other individuals with identifying information removed.

In the UK, approximately one in 14 people over the age of 65 and one in six over the age of 80 develop dementia, says Stewart. The analysis found that the rugby union players were 2.2 times more likely to develop dementia than the rest of the population.

It also found that rugby players were 3.0 times more likely to develop Parkinson鈥檚 disease than people in the general population and 15.2 times more likely to develop motor neurone disease.

Over a median of 32 years, 11.4 per cent of the rugby players were diagnosed with a neurodegenerative disease, compared with 5.4 per cent of the comparison group. Neurodegenerative disease was the primary cause of death in 2.7 per cent of the rugby players, compared with 1.5 per cent in the general population group.

Stewart says the rise in motor neurone risk in rugby players was the most shocking result in the study. The team is now trying to figure out why rugby union players may face such a high risk of developing the disease. 鈥淚t鈥檚 a priority,鈥� says Stewart.

The increase in neurodegenerative disease is probably due to the athletes sustaining a greater number of head injuries. 鈥淲hen we have the opportunity to examine the brains of people who have participated in contact sports and develop dementia, we find this unique pathology in the brains,鈥� says Stewart. 鈥淚t鈥檚 something we only see in people who have been exposed to brain injury and we don鈥檛 see anywhere else.鈥�

Many of the rugby players in this analysis played the game at a time when the game was amateur and so had other jobs as well. Professional rugby players today probably devote much more time to playing and training, and may face even greater risks, says Stewart.

鈥淣ow the game鈥檚 become more intense,鈥� he says. 鈥淔rom the advent of the professional game, people have grown fitter, faster, heavier and stronger. The number of matches has gone up, concussion levels have gone up and so you know it鈥檚 much more physically demanding than it used to be. You would have to imagine that the risk is higher than it鈥檚 ever been.鈥�

Stewart says he hopes that rugby鈥檚 leaders take the research seriously. 鈥淲e might have to take the difficult decision and say that the number of games of rugby being played at the moment is unacceptably high. And perhaps we need to try and reduce contact training as much as possible,鈥� he says.

鈥淭his study is further evidence supporting an increased risk of neurodegenerative disease amongst rugby players, including dementia, Parkinson鈥檚 and motor neuron disease, similar to previous studies in American football and soccer players,鈥� says at Boston University.聽鈥淭here is an immediate need to protect active players from the long-term consequences of repetitive head impacts across all contact sports, including rugby, soccer, American football, ice hockey and boxing.鈥�

脡anna Falvey, the chief medical officer of World Rugby, said in a statement:聽鈥淎t World Rugby we have an independent concussion working group that considers all the latest academic research and findings. This enables us to have a constant and open conversation about what changes to the game may be appropriate and where further research may need to be focused to help us drive forward our player welfare plan.

鈥淲orld Rugby will never stand still on player welfare. To date, we have invested over 鈧�10 million in welfare studies including the largest study into head impacts in community sport anywhere in the world and a study of health outcomes for over 3,000 retired rugby players, both delivered in partnership with New Zealand Rugby. We will continue to build on this work in our quest to make our game as safe as it can possibly be for players at all levels within the rugby family.鈥�

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