A new study confirms something pediatricians and parents already suspected: One key to having happy, healthy and less depressed children is to have earlier bedtimes.

The study was conducted by researchers at Columbia University and appears in the journal Sleep. It shows that adolescents and teens with strict bedtimes of 10 p.m. or earlier were less likely to be depressed and to have suicidal thoughts than classmates whose parents allowed them to stay up until midnight or even later.

Another study published in the Journal of Adolescent Health examined the sleep habits of more than 12,000 high school students and found that a mere 8 percent are getting at least the recommended nine hours of sleep per night.

The Columbia researchers found that bedtimes set by parents were almost as important as the total number of hours slept. Kids who were sent to bed at midnight or later were 24 percent more likely to be depressed and 20 percent more likely to have thoughts about suicide compared to teens whose lights had to be off by 10 p.m.

The researchers surveyed 15,000 children in grades 7-12 and their parents and found that more than two-thirds of the adolescents said they went to bed when they were supposed to. For 54 percent of kids, that's 10 p.m. or earlier on school nights. Another 21 percent must go to bed by 11 p.m., and 25 percent go to bed at midnight or later.

The teens were also asked to fill out depression questionnaires and were asked whether they'd seriously thought about suicide over the past year.

Scientists have long known that there was a link between depression and poor sleep. But there has always been a question as to whether the depression caused insomnia or whether poor sleep led to depression. The fact that parent-enforced bedtimes play such a significant role suggests lack of sleep may actually be a cause, not just an effect of depression.

As you know, I believe it's critical for all teens to have a firm bedtime. Begin winding down their night by turning off all electronics 1/2 hour before they head to bed. There should be no TV on in the background and cell phones should be charging on the family docking station in the kitchen.

Tuck your teen in tonight at a reasonable hour. It's good for both parent and teen.

Dr. Sue Hubbard is a nationally known pediatrician and co-host of "The Kid's Doctor" radio show.

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