Children who go to bed earlier have lower risk of depression than those who stay up much later, anew study shows.

Going to bed at 10 p.m. may help children quell suicidal thoughts as well, according to the study by researchers at Columbia University Medical Center in New York City.

The research findings were presented on Tuesday at the Associated Professional Sleep Societies annual meeting that opened in Seattle on Monday.

The study stemmed from data on more than 15,000 adolescents who participated in the National Longitudinal Study of Adolescent Health.

The researchers found that 1,143 of the teens were depressed and 2,038 had suicidal ideation, the term clinicians use to describe suicidal thinking.

When researchers looked at the relationship of depression and suicidal thoughts to parental-mandated bedtimes, they found a clear correlation.

Teens whose parents insist on 10 p.m. or sooner for lights out were 25 percent less likely to be depressed and 20 percent less likely to have suicidal thoughts, compared with kids who hit the sack at midnight or later, according to the study.

The researchers adjusted the data to account for numerous factors, including parental connectedness and the age of the teens, because older teens probably would have later bedtimes. After controlling for these factors, it was clear that a lack of sleep was to blame for the increased risk of depression and suicidal thoughts, said the study.

"This study bolsters the argument that a lack of sleep can cause depression," said study author James Gangwisch, an assistant professor of psychiatry. "Teens with earlier parental-mandated bedtimes were less likely to suffer from depression and suicidal thoughts."

"Kids that have to go to bed earlier are getting more sleep," he said.

Gangwisch said most teens need at least eight to nine hours of sleep a night, and parents might underestimate their teens' need for sleep.

Besides increasing the risk for depression and suicidal thoughts, a lack of sleep can affect a child's focus and learning, according to the study.

A dearth of sleep is also associated with obesity and type 2 diabetes, said the study.

(Xinhua News Agency June 10, 2009)