It's all the more reason that parents should try to monitor how much their kids are sleeping, Roberts tells Shots. "Kids should go to bed at a regular time. They should wake up at a regular time. They should have a dark room if possible — that means no TV, no games, no phones."
A lot of adolescents just aren't getting as much sleep at they should. The Centers for Disease Control and Prevention recommends nine to 10 hours, but 70 percent of high schoolers don't meet that requirement
In a second study, researchers in Sweden found that lack of sleep and excessive media use were associated with mental health problems in teens.
The researchers from Karolinska Institutet in Stockholm collected data from over 12,000 European adolescents. They were looking for behaviors that were most associated with depression and suicide in teens.
It came as no surprise that teens who misused drugs and skipped school were more likely to have depression, says Danuta Wasserman, one of the study's authors and the director of Karolinska 's National Centre for Suicide Research and Prevention.
But the teens who engaged in risky behaviors weren't the only ones who showed depressive symptoms. Depression and suicidal thoughts were just as common among kids who didn't sleep and exercise enough, and who spent a lot of time on the Internet. Both groups were over three times as likely to have depression as the rest of their peers.
Wasserman says she and her colleagues decided to call the latter the "invisible risk" group, because most parents and teachers didn't realize that the kids in that group were hurting. The study was published Monday in the Journal Word Psychiatry.
Wasserman says more research needs to be done before we can know how Internet use affects depression, and how depressed kids are likely to use the Internet. It could be a way to avoid social interaction, but it could also be a place where kids seek out help, she says.
But Wasserman says that she wasn't surprised that teens in this invisible risk group weren't getting enough sleep.
There's plenty of evidence on the link between sleep problems and depression in teenagers and adults. But teens are especially susceptible to loosing sleep. During puberty, circadian rhythms change, and teens want to sleep and wake up later, Roberts says.
At the same time, in high school homework gets harder, kids start to take on part time jobs, and their social lives amp up.
"When you throw in all the video games and iPods and all the phones," Roberts says, sleep starts to become less of a priority.
Early school start times don't help, he says. Parents all over the country are petitioning for legislation that would move high school start times later.