Jan. 1, 2010 -- Adolescents whose parents set earlier bedtimes are significantly less likely to suffer from depression or have suicidal thoughts compared to youngsters who hit the sack later, new research indicates.

Youngsters in the study whose parents set bedtimes of midnight or later were 24% more likely to suffer from depression and 20% more apt to have thoughts of suicide, compared to youngsters with bedtimes of 10 p.m. or earlier, researchers report in the Jan. 1 issue of the journal SLEEP.

This suggests sufficient sleep may offer youngsters some protection from depression and thoughts of suicide, the researchers say.

Adolescents who reported they usually sleep five or fewer hours per night were 71% more likely to report depression, and 48% more likely to have thoughts of committing suicide, compared to young people reporting eight hours of sleep nightly, the study shows.

"Our results are consistent with the theory that inadequate sleep is a risk factor for depression," says study researcher James E. Gangwisch, PhD, of Columbia University Medical Center in New York.

He and his colleagues collected data on 15,659 adolescents and their parents who had participated in the National Longitudinal Study of Adolescent Health, a school-based sample of students in seventh to 12th grades, between 1994 and 1996.

The researchers found that:

The average sleep duration was 7 hours and 53 minutes. The researchers note that adolescents need 9 hours of sleep daily.

Nearly 70% of youngsters said they went to bed at a time that complied with the weeknight limit set by their parents.

The researchers say lack of sleep may produce moodiness that hinders the ability to cope with stresses of daily life, harming relationships with peers and adults. They say educating adolescents and their parents about the benefits of healthier sleep practices may be beneficial.

The researchers conclude that parents of adolescents should set earlier bedtimes to make sure their teens get adequate sleep.

One of the researchers, Gary K. Zammit, PhD, of Columbia, reported receiving research support from GlaxoSmithKline and other pharmaceutical companies. He also disclosed he has financial interests in two companies involved in sleep research.