Sleepwalking affects 3.6 per cent of adults in the U.S., more than previously thought, a new study suggests.

Sleepwalking was not associated with gender and seemed to decrease with age. (Michaela Rehle/Reuters)

Dr. Maurice Ohayon, a professor of psychiatry and behavioral sciences at Stanford University, and his co-authors set out to estimate the prevalence of sleepwalking in the U.S., since the most recent research on the topic was done 10 years ago in Europe. The only U.S. sleepwalking prevelance rate study was published 30 years ago. That study reported a prevalence of 2.5 per cent of sleepwalking in a sample of 1,006 adults living in the Los Angeles metropolitan area.

"This study, based on a large representative sample of the U.S. general population, is the first to demonstrate the prevalence of nocturnal wandering in the community," Ohayon and his co-authors concluded in Tuesday's issue of the journal Neurology.

"Precisely, 3.6 per cent of the sample had more than one episode of nocturnal wandering in the previous year."

The researchers surveyed nearly 19,136 individuals from 15 states by phone to gather information on participants' mental health, medical history and medication use.

The participants were asked about the frequency of episodes of sleepwalking, how long any sleep disorders lasted and about any inappropriate or potentially dangerous behaviours during sleep.

Sleepwalking episode may not be remembered

When respondents' answers about episodes of sleepwalking during childhood or adolescence were included, the lifetime prevalence of sleepwalking was 29.2 per cent.

What's not known is whether medical conditions provoke sleepwalking or vice-versa, Ohayon said.

Among those who reported sleepwalking, it was mainly chronic. About 7.2 per cent of respondents had episodes for less than six months, 5.8 per cent for 6 to 12 months, and another 6.2 per cent had it for one to five years and 80.2 per cent for more than five years.

Nearly 40 per cent of the respondents worked a day-time shift.

Other findings included:

• Sleepwalking was not associated with gender and seemed to decrease with age.
• Nearly one-third of individuals with nocturnal wandering had a family history of the disorder.
• People with depression were 3.5 times more likely to sleepwalk than those without.
• People with alcohol abuse or dependence or obsessive-compulsive disorder were also significantly more likely to have sleepwalking episodes.
• People using over-the-counter sleeping pills had a higher likelihood of reporting sleepwalking episodes at least two times per month.

In most of the cases of sleepwalking among those taking psychotropic medication, such as antidepressants or hypnotics, the patient was awake but confused and did not remember the episode after waking up.

"It seems unlikely that these medications cause nocturnal wandering, but rather that they appear to trigger events in predisposed individuals," the researchers said.

Since there is no objective measure of sleepwalking, and amnesia is a characteristic, it is likely that sleepwalking is underreported, especially among those living alone, they concluded.

The study was funded by the U.S. National Institutes of Health, the Arrillaga Foundation, the Bing Foundation and an educational grant from Neurocrines Biosciences.