The research, led by consultant neuropathologist Prof Willie Stewart, compared health outcomes among 412 male, Scottish, former international rugby players and over 1,200 matched individuals from the general population.
In its findings, the report said the ex-players had more than twice the risk of a neurodegenerative disease and an over 10-fold risk of motor neuron disease diagnosis.
The statistics have led to calls for the adoption of measures in rugby to reduce unnecessary head impacts by cutting back on the number of games and ending full-contact training sessions.
Weir, the former Scotland forward who was diagnosed with MND in 2016, has campaigned tirelessly to improve the lives of those with the disease and to raise funds for more research.
He believes his rugby career was not the cause of his diagnosis and believes there is still work to be done to prove the link between the sport and MND.
“Any research to help us better understand MND is welcome,” said Weir in a statement released by the My Name’5 Doddie Foundation.
“This study certainly has some surprising findings but we are still not clear on any proven links between rugby and the cause of MND.
“I have always believed that my rugby career did not lead to me being diagnosed with this terrible disease. My Name’5 Doddie Foundation continues to commit significant funds into MND research that will help us to understand its causes.”
Jessica Lee, director of research at My Name’5 Doddie Foundation, said the latest study should be viewed with caution because the sample size was “relatively small”.
“Whilst these results are concerning, the findings should be viewed with caution,” said Lee.
“The sample size included in the study is relatively small, especially when studying an uncommon condition like MND. These findings therefore warrant further investigation in larger scale studies.
“Whilst the study showed a correlation between Scottish international rugby players and the incidence of MND, it did not provide evidence of a causal relationship. Further research is needed to better understand whether playing elite sport, including rugby, could lead to the development of MND.”
Prof Stewart is Honorary Professor at the University of Glasgow and led the landmark FIELD study which reported the first data on neurodegenerative risk among former professional footballers.
He said the rugby study raised immediate questions for the sport’s authorities to mitigate the risks, with the game’s leaders being urged to eliminate contact training and reduce rather than expand the global calendar.
“I am genuinely concerned about what is happening in the modern game, and that if, in 20 years’ time, we repeat this study we would see something even more concerning,” Stewart said.
He added: “Of particular concern are the data on motor neuron disease risk among our rugby players, which is even higher than that for former professional footballers. This finding requires immediate research attention to explore the specific association between rugby and the devastating condition of motor neuron disease.”