A study in the Jan. 1 issue of the journal Sleep found that adolescents with bedtimes that were set earlier by parents were significantly less likely to suffer from depression and to think about committing suicide, suggesting that earlier bedtimes could have a protective effect by lengthening sleep duration and increasing the likelihood of getting enough sleep.

Results show that adolescents with parental set bedtimes of midnight or later were 24 percent more likely to suffer from depression (odds ratio = 1.24) and 20 percent more likely to have suicidal ideation (OR=1.20) than adolescents with parental set bedtimes of 10 p.m. or earlier. This association was appreciably attenuated by self-reported sleep duration and the perception of getting enough sleep. Adolescents who reported that they usually sleep for five or fewer hours per night were 71 percent more likely to suffer from depression (OR=1.71) and 48 percent more likely to think about committing suicide (OR=1.48) than those who reported getting eight hours of nightly sleep. Participants who reported that they "usually get enough sleep" were significantly less likely to suffer from depression (OR=0.35) and suicidal ideation (OR=0.71).

Lead author James E. Gangwisch, PhD, assistant professor at Columbia University Medical Center in New York, N.Y., said that the results strengthen the argument that short sleep duration could play a role in the etiology 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 preventative measure against depression and a treatment for depression."

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 U.S. students in grades seven to 12 in 1994 to 1996. Seven percent of participants (1,050) were found to have depression using the Centers for Epidemiologic Study-Depression Scale, and 13 percent (2,038) reported that they seriously thought about committing suicide during the past 12 months. Depression and suicidal ideation were associated with later parental set bedtime, shorter sleep duration, self-perception of not getting enough sleep, female sex, older age and lower self-perception of how much parents care.

Fifty-four percent of parents reported that their adolescent had to go to bed by 10 p.m. or earlier on weeknights, 21 percent reported setting a bedtime of 11 p.m., and 25 percent reported setting a bedtime of midnight or later. Caucasians were more likely than adolescents of other racial/ethnic groups to have a parental set bedtime of 11 p.m. Nearly 70 percent of adolescents reported going to bed at a time that complied with the weeknight bedtime that was set by their parents. Adolescents reported going to bed only about five minutes later on average than their parental set bedtime.

The average adolescent-reported sleep duration was seven hours and 53 minutes, which contrasted sharply with the nine or more hours of nightly sleep that the AASM recommends for adolescents. Participants with a parental set bedtime of 10 p.m. or earlier reported that they usually slept for an average of eight hours and 10 minutes, which was 33 minutes more than adolescents with a bedtime of 11 p.m. (seven hours, 37 minutes) and 40 minutes more than those with a bedtime of midnight or later (seven hours, 30 minutes). With the exception of sleep durations of 10 hours or more per night, higher average self-reported sleep durations were associated with progressively earlier average bedtimes.

The authors reported that there are a number of potential mechanisms by which chronic partial sleep deprivation could contribute to depression and suicidal ideation. A lack of sleep may affect the modulation of emotional brain responses to aversive stimuli; produce moodiness that hinders the ability to cope with daily stresses and impairs relationships with peers and adults; and affect judgment, concentration and impulse control.

They also suggested that behavioral interventions that involve educating adolescents and their parents about healthier sleep hygiene practices and helping them modify maladaptive sleep habits could sever as primary preventative measures against depression and suicidal ideation.