It shows that adolescents with parental-set bedtimes of midnight or later were 24 percent more likely to suffer from depression and 20 percent more likely to have suicidal thoughts than those with parental-set bedtimes set for 10 p.m. or earlier.
Those who reported sleeping five or fewer hours per night were 71 percent more likely to suffer from depression and 48 percent more likely to think about committing suicide than those who reported eight hours of sleep.
Also, participants who reported that they "usually get enough sleep" were significantly less likely to suffer from depression and suicidal ideation.
James E. Gangwisch, assistant professor at the Columbia University Medical Centre (CUMC), who led the study, said the results strengthen the argument that short sleep duration could play a role in a person's history of depression.

"Our results are consistent with the theory that inadequate sleep is a risk factor for depression, working with other risk and protective factors through multiple possible causal pathways to the development of this mood disorder," said Gangwisch.
"Adequate quality sleep could, therefore, be a preventive measure against depression and a treatment for the disease," added Gangwisch, according to a CUMC release.
Data were collected from 15,659 adolescents and their parents who had participated in the National Longitudinal Study of Adolescent Health (Add Health), a school-based, nationally representative, probability-based sample of US students in grades seven to 12 in 1994 to 1996.

The study was published in the Friday issue of Sleep.