New research suggests that people who physically act out their dreams are at higher risk of developing neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease.

During REM, or rapid eye movement, sleep, the muscles relax and do not move, but in idiopathic REM sleep behaviour disorder people have episodes of excessive muscle activity, and essentially act out their dreams by punching, kicking, and etcetera.  

Researchers studied 93 people with REM sleep disorder, but who had no signs or symptoms of neurodegenerative diseases. The average age of participants at the start of the five-year-long study was 65. Results showed that more than a quarter of participants were diagnosed with a neurodegenerative condition over the next five years.  Fourteen developed Parkinson's disease, 7 developed a rare form of dementia called Lewy body dementia dementia, and 4 met clinical criteria for Alzheimer's disease. One participant developed multiple system atrophy, a rare disorder that affects movement, blood pressure and other body functions.

Using the results, the researchers estimated that patients of a similar age with idiopathic REM sleep disorder would have a more than a 50/50 chance of developing a neurodegenerative disease within the next 12 years.

The researchers concluded: “The risk of developing neurodegenerative disease in idiopathic REM sleep behavior disorder is substantial, with the majority of patients developing Parkinson disease and Lewy body dementia.”

Postuma RB, Gagnon JF, Vendette M, Fantinit ML, Massicotte-Marquez J. Montplaisie J. Quantifying the risk of neurodegenerative disease in idiopathic REM sleep behavior disorder. Neurology Published online before print December 24, 2008. doi:10.1212/01.wnl.0000340980.19702.6e