Kicking in sleep could mean you are more likely to develop dementia or Parkinson's, scientists warn.

They say it could signal a higher risk up to 50 years before diagnosis.

Researchers found a link between people with rapid eye movement (REM) sleep behaviour disorders and brain conditions many years later, says a Daily Mail report.

REM sleep is the stage in which people dream. Most sleepers are 'paralysed' because the brain shuts off the muscles.

But this doesn't happen to those with REM sleep behaviour disorders, who often act out their dreams with violent movements.

Those with the condition have been known to break a hand, hurt a partner or fall off bed.

The research published in the medical journal Neurology adds to evidence that certain sleep disorders could be predictors of brain diseases.

This raises the possibility that doctors could one day be able to provide earlier diagnoses.

Study author Bradley Boeve, from the Mayo Clinic in Rochester, Minnesota, said: 'Our findings suggest that in some patients, these conditions have a very long span of activity within the brain and they may also have a long period of time where other symptoms aren't apparent.'

Using Mayo clinic records, researchers identified dozens of people who experienced REM sleep disorders for at least 15 years before developing either Parkinson's, dementia with Lewy bodies or multiple system atrophy - a disorder similar to Parkinson's.

The time between the start of the sleep disorder and the symptoms of brain disease ranged up to 50 years, with an average span of 25 years.