The study of nearly 16,000 teenagers in grades 7 to 12 found that adolescents with bedtimes set at midnight or later were 24 percent more likely to suffer from depression than those with bedtimes of 10 p.m. or earlier. Teenagers with later bedtimes also were 20 percent more likely to have suicidal thoughts.
The study was published in the January issue of the journal Sleep.
Depression and poor sleep often go hand in hand, but sleep difficulties are usually seen as a symptom of depression, not a cause, says James Gangwisch, PhD, assistant professor in the Department of Psychiatry and lead investigator of the new study.
To see if sleep deprivation can lead to depression, researchers would have to alter teenagers’ sleep schedules and record the results. Such an experiment would be unethical, given other known detriments of sleep deprivation, and too expensive with large numbers of teenagers.
Instead, Dr. Gangwisch did the next best thing. He gathered data from a “natural experiment”: what happened when teenagers had their bedtimes imposed by their parents. These data on bedtime and depression came from a previous survey, the National Longitudinal Study of Adolescent Health, conducted between 1994 and 1996.
“Depression in adolescents can affect their choice of bedtime, but it’s less likely to affect their parents’ choice,” Dr. Gangwisch says, “By using data from the survey, we got some of the benefits of a large experimental study without the drawbacks.
“Together with smaller studies that have shown sleep deprivation alters mood in teenagers, our finding is strong evidence that inadequate sleep plays a role in causing depression.”
The reasons why sleep deprivation may lead to depression, though, are still unclear. Dr. Gangwisch says moodiness from a lack of sleep may interfere with a teenager’s ability to cope with daily stress or impair relationships with friends and family. Suicidal thoughts may increase due to the effects of insufficient sleep on judgment, aggression, and impulse control.
Of course, telling teenagers to go to bed at 10 p.m. does not mean they will actually go to sleep. But nearly 70 percent of the teenagers in the study reported going to bed at or before bedtimes set by their parents.
“The biggest question I get from parents is how to get their teenagers to bed earlier,” Dr. Gangwisch says. “I think it’s a matter of motivating teenagers to see the benefits. I’d encourage teenagers to try a few nights of eight or nine hours of sleep and see if they feel better during the day.
“In our society we think we can cut back on sleep to be more productive during the day, but the loss of concentration, energy, motivation, and now mood changes resulting from insufficient sleep can make us less productive during the day, making the extra time devoted to sleep well worth it.”