NEW YORK (Reuters Health) – Overweight children tend to sleep less than their thinner peers, spending less time in the “dream” stage of sleep in particular, according to a study published Monday.

The findings, reported in the Archives of General Psychiatry, add to evidence that sleep deprivation might contribute to excess pounds in adults and children. They are also the first to suggest that REM sleep may be especially important in weight control.

REM (for “rapid eye movement”) sleep is the stage in which vividly remembered dreams usually occur. Research also suggests that sleep metabolism is highest during REM sleep compared with other sleep stages, and that a lack of REM sleep may be particularly likely to spur hormone changes that increase appetite.

For the current study, researchers at the University of Pittsburgh School of Medicine had 335 children and teenagers each spend three consecutive nights in the sleep lab. The children wore electrodes that recorded their brain activity and other physiologic functions as they slept.

The researchers found that, on average, overweight children slept for 22 minutes less than normal-weight children did. They also took longer to enter the REM stage of sleep and spent less time in REM sleep overall.

In general, the study found, each one-hour decrease in total sleep time made it twice as likely that a child was overweight. The risk linked to REM sleep was even greater; for every hour of REM sleep a child lost, the odds of being overweight tripled.

“This represents the first study to report specifically that REM sleep seems to be the stage most strongly associated with childhood overweight,” write Dr. Xianchen Liu and colleagues.

The reasons for the link between sleep deprivation and excess weight are not firmly established.

However, Liu’s team notes, there is evidence that poor sleep has hormonal effects that could lead to weight gain — including a decrease in the appetite-suppressing hormone leptin and an increase in the hunger-stimulating hormone ghrelin.

For its part, REM sleep has been shown to be the most metabolically active sleep stage; a decrease in this sleep stage would lower overnight calorie burning. What’s more, some research suggests that leptin, ghrelin and other hormones may be especially sensitive to changes in REM sleep.

Whatever the reason for the link between REM sleep and children’s weight, the results underscore the importance of a good night’s sleep, according to the researchers. In general, experts recommend that children between the ages of 5 and 12 get 10 to 11 hours of sleep each night, while teenagers should get 8.5 to 9.5 hours.

SOURCE: Archives of General Psychiatry, August 2008.