An international team, led by researchers at Montreal General Hospital in Canada, has found that physically "acting out" dreams when asleep could well be an early warning sign of dementia or Parkinson's disease.

In fact, the researchers have based their findings on an analysis of shut-eye patterns of 93 people with "REM sleep behaviour disorder", which involves either punching or kicking out while dreaming.

The subjects were elderly, on an average 65 years old, which already put them at higher risk of developing dementia compared with a younger person. Each was followed on average for five years, and in that period, 26 of the 93 developed a degenerative brain disease.

In total, 14 were diagnosed with Parkinson's disease, seven with Lewy body dementia, four with Alzheimer's Disease, and another diagnosed with a disorder called multiple system atrophy which involves both Parkinson's and dementia symptoms.

And, their predictions suggested that patients of this age with the same sleep disorder would actually have a greater than 50/50 chance of falling prey to a similar condition over the next 12 years.

According to the researchers, knowing more about the risks faced by people with the sleep disorder could not only help doctors to advise their patients, but also to work in the years to come to come up with ways to protect them.

Dr Susanne Sorensen, Head of Research at Alzheimer's Society, said that the findings were particularly interesting in relation to Lewy body dementia, which accounts for only four per cent of dementia cases, 'BBC News' portal reported.

"People with Lewy body dementia often have vivid nightmares, restless sleep and hallucinations – this study suggests that people with the disease may experience sleep disorders years before their other symptoms develop.