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If you smoke, have had a head injury, or have been exposed to pesticide, you may be at risk for a rare sleep disorder that causes people to kick or punch during sleep, according to a study published in the June 27, 2012, online issue of Neurology®, the medical journal of the American Academy of Neurology.

The rapid eye movement (REM) sleep behavior disorder causes people to act out their dreams in sometimes violent, injury-causing movements. The disorder is estimated to occur in 0.5 percent of adults.

"Until now, we didn't know much about the risk factors for this disorder, except that it was more common in men and in older people," said study author Ronald B. Postuma, MD, MSc, with the Research Institute of the McGill University Health Centre (MUHC) in Montreal and a member of the American Academy of Neurology. "Because it is a rare disorder, it was difficult to gather information about enough patients for a full study. For this study, we worked with 13 institutions in 10 countries to get a full picture of the disorder."

Researchers studied nearly 350 people with REM sleep behavior and nearly 350 without and found that:

Those with REM sleep behavior disorder were 43 percent more likely to be smokers, with 64 percent of those with the disorder having ever smoked, compared to 56 percent of those without the disorder

They were 59 percent more likely to have had a previous head injury with loss of consciousness, 67 percent more likely to have worked as farmers, and more than twice as likely to have been exposed to pesticides through work

Those with the disorder also had fewer years of education, with an average of 11.1 years, compared to 12.7 years for those without the disorder.

Previous research has shown that more than 50 percent of people with REM sleep behavior disorder go on to develop a neurodegenerative disorder, such as Parkinson's disease, years or even decades later.

"Due to this connection, we wanted to investigate whether the risk factors for REM sleep behavior disorder were similar to those for Parkinson's disease or dementia," Postuma said.

The results were mixed. While smoking has found to be a protective factor for Parkinson's disease, people who smoked were found to be more likely to develop REM sleep behavior disorder. Pesticide use, on the other hand, is a risk factor for both disorders. Studies have shown that people who drink coffee are less likely to develop Parkinson's, but this study found no relationship between coffee drinking and REM sleep behavior disorder.