The figure is likely to send shock waves through the sport, which is already embroiled in a legal fight over the link between concussion and early onset dementia and which is scrambling to find ways of reducing incidences of concussion in matches and training at all levels.
In findings published in the Journal of Neurology, Neurosurgery and Psychiatry on Tuesday, researchers found that the players group had an approximately two and a half times higher risk of neurodegenerative disease than expected but that player position had no impact on risk.
The stand-out result were the figures for MND, a condition that has been brought into the rugby spotlight by the suffering of former Scotland lock Doddie Weir and former Great Britain rugby league halfback Rob Burrow.
Led by consultant neuropathologist Willie Stewart, Honorary Professor at the University of Glasgow, the FIELD research team compared health outcomes among 412 male former Scottish international rugby players and over 1200 matched individuals from the general population.
The study is a continuation of research made by the same organisation into neurodegenerative risk among former professional footballers and players, and also found similarities with the NFL.
"This latest work demonstrates that risk of neurodegenerative disease is not isolated to former footballers, but also a concern for former rugby players," Stewart told journalists.
"It provides further insight into the association between contact sports and neurodegenerative disease risk. Of particular concern are the data on MND risk, which is even higher than that for former footballers. This finding requires immediate research attention to explore the specific association between rugby and the devastating condition of MND."
The findings come against the backdrop of a group of almost 200 former players taking legal action against World Rugby, the Rugby Football Union and the Welsh Rugby Union.
The claimants, who include England's 2003 World Cup-winning hooker Steve Thompson, argue the sport's governing bodies were negligent in that they were aware of the risk but failed to take reasonable action to protect players from permanent brain injury and subsequent early-onset dementia caused by repetitive blows to the head.
Thompson was diagnosed with early onset dementia in 2020.
In recent years rugby has implemented changes to the tackle law and moved towards a reduction in contact training in a bid to minimise head impacts but Stewart urged more and quicker action.
"I think rugby could be speeding up this pace of change," he said.
"Rugby has to think about it. You can't continue to put young men and women through what they've been put through, now we know that, even from amateur era, there is this risk of degenerative brain disease."
