People who punch or kick out in their sleep are more likely to develop dementia or Parkinson's disease, research revealed today.
Scientists studied 93 people with "REM sleep behaviour disorder", the symptoms of which can include lashing out during dreams.
The study found 26 patients went on to be diagnosed with a degenerative brain condition over the next five years.
Of those, 14 developed Parkinson's Disease, seven developed a rare form of dementia called Lewy body dementia and five standard dementia. The other patient developed multiple system atrophy, which involves both Parkinson's and dementia symptoms.
During the dream state REM, or Rapid Eye Movement, a person's muscles normally relax but people with certain sleep disorders can lash or cry out. Sufferers of certain degenerative brain diseases, including Parkinson's disease and Lewy body dementia, can also exhibit similar symptoms.
The Canadian study concluded: "Although we have found a slightly lower risk than other reports, the risk of developing neurodegenerative disease in REM sleep behaviour disorder is substantial, with the majority of patients developing Parkinson disease and Lewy body dementia."
Volunteers for the tests, published in US publication Neurology, were aged on average 65 years old.
Dr Susanne Sorensen, head of research at the Alzheimer's Society, said the research could help doctors to predict the onset of dementia, which an estimated 700,000 people in the UK currently suffer from.
She told the BBC: "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.
"This important finding could boost our understanding of how Lewy body dementia develops and help us detect it early. With further research we may be able to stop this devastating disease in its tracks."Reuse content