Everyone dreams. But less than 1 percent of adults have a rare condition that causes them to act out their dreams while asleep.

During a vivid dream involving lots of action, people with REM sleep behavior disorder, (RBD) may punch, kick, scream, shout, swear or grab someone while sleeping or they may jump out of bed -- injuring themselves or hurting a bedmate in the process.

RBD episodes happen during rapid-eye-movement (REM) sleep, a stage of shut-eye when dreaming occurs, or roughly every two hours.

Usually the body is "paralyzed" during REM sleep. But this doesn't happen in people with RBD, so their arms and legs are free to move while dreaming. As a result, if someone with RBD is dreaming of being attacked, they may fight back in their sleep. There's medication to treat RBD symptoms, yet doctors have previously known little about who is affected by the disorder other than it is more common in men and typically strikes people after age 50.

For reasons that are still unclear, REM sleep behavior disorder also seems to increase a person's risk for Parkinson's disease and one type of dementia. Some studies have suggested that more than 50 percent of those with this rare sleep disorder may go on to develop a neurodegenerative disease.

To learn more, a recent study published in the journal Neurology tried to determine the risk factors for RBD and whether they were similar to those for Parkinson's disease or dementia.

They compared the lifestyle habits of 347 people with RBD to the same number of people who didn't have this sleep problem but were similar in age and gender.

The study identified several potential risk factors for RBD, including having a previous head injury, being a farmer, and working in a job with pesticide exposure. All three of these risks have also been linked with Parkinson's disease.

Researchers also found that people who had fewer years of education increase their chances of RBD.

"Many of the risk factors for RBD are the same as for Parkinson's disease, however, it is ultimately where they differ that can teach us the most," says study author Dr. Ronald Postuma, a neurologist and associate professor at McGill University in Montreal, Canada.

One important difference scientists found was that people who smoke were more likely to develop RBD, but nicotine has been shown to reduce the odds of Parkinson's disease. A second difference is that coffee drinking was not linked with the sleep disorder while other studies have suggested it helps protect against Parkinson's disease.

Postuma suspects that in some people, REM sleep behavior disorder can be an important sign of early Parkinson's disease. In these early stages, he says the disease may affect areas of the brain involved in sleep, smell, and bladder control.

As Parkinson's advances, it affects the motor areas of the brain, producing symptoms such as tremors, rigid muscles, and problems with walking or posture.

Someone who is acting out their dreams at night often first learns they're doing this from their sleep partner. Sleep talking or sleep walking is usually something quite different from RBD, points out Postuma.

A specialist at a sleep clinic can confirm the diagnosis. Postuma also recommends that RBD patients should be followed by a neurologist, who can monitor and treat their symptoms should any Parkinson changes emerge.