Teens surveyed for a U.S. study said they got seven hours and 53 minutes of sleep on average a night, compared with the nine or more hours recommended by sleep experts. (iStock)

Earlier bedtimes may help protect teens from depression and suicidal thoughts, says a U.S. study published Friday.

Researchers analyzed data from 15,659 U.S. students in Grades 7 to 12 and their parents. Participants were surveyed from 1994 to 1996 for the study by James Gangwisch, a professor of psychiatry at Columbia University Medical Center in New York, and his colleagues .

On average, the teenagers said they got seven hours and 53 minutes of shut-eye a night, compared with the nine or more hours recommended for adolescents by the American Academy of Sleep Medicine, the team reported in the journal Sleep.

Adolescents who reported that they usually slept five or fewer hours a night were 1.71 times more likely to suffer from depression and 1.48 times more likely to think about committing suicide than those who said they got eight hours of sleep a night. These calculations took into account demographic factors such as race and whether the family received public assistance, the study said.

"Our findings suggest that later parental-set bedtimes contribute to shorter sleep durations and perceptions of not getting enough sleep, which in turn are associated with depression and [thoughts of suicide]," the study's authors concluded.

By setting earlier bedtimes, parents could protect against depression and suicidal thoughts in their children, the authors said.

Participants who reported that they "usually get enough sleep" were 0.35 times less likely to suffer from depression and 0.71 times less likely to think of committing suicide, the researchers found.

Seven per cent of the teens surveyed, or 1,050, were found to have depression based on a standard depression scale. Thirteen per cent, or 2,038, reported they had seriously thought about committing suicide in the past 12 months.

Bedtime compliance

Participants with a parent-set bedtime of 10 p.m. or earlier reported sleeping an average of eight hours and 10 minutes — 33 minutes more than teens with a bedtime of 11 p.m., and 40 minutes more than those with a bedtime of midnight or later.

Two-thirds of participants said they complied with the bedtime rules.

The researchers presented several possible reasons why chronic partial sleep deprivation could contribute to depression and suicidal thoughts. For instance, they said, lack of sleep may:

• Affect how the emotional brain responds to unpleasant stimuli.
• Produce moodiness that reduces the ability to cope with daily stresses and impairs relationships with peers and adults.
• Hinders judgment, concentration and impulse control.

The authors cited limitations in the study, including the use of self-reported sleep times and a lack of questions about school start times.

The study was funded by the Robert Wood Johnson Health and Society Scholars Program at Columbia. One of the study author's reported funding and consulting ties with several pharmaceutical companies.