Most adults think they know what to look for in depressed teens. They might be missing school or suddenly started drinking or using drugs. According to a new study, they might be overlooking some other warnings.

Too much time with media, too little activity and not enough sleep can signal—or trigger—depression in teens just as surely as a host of other, more easily recognizable warning signs, according to a new study published in World Psychiatry recently.

For the study, scientists surveyed more than 12,000 students in Europe between the ages of 14 and 16 and asked them about eight potential risk factors for depression: excessive drinking, using drugs, smoking heavily, truancy, high media use, lack of sleep, a lack of exercise and weight issues (either being overweight or underweight).

About 13 percent of the teens surveyed were high in every possible category, and of these high-risk kids, about 15 percent reported signs of depression (compared to 4% of teens who scored low in these risk categories).

Researchers also found that the 29 percent of teens who had high scores in media usage, lack of sleep and lack of exercise—forming what researchers call the invisible risk group—were almost as prone to be depressed (13% of them) as those who scored high in all risk categories. (Time)

Paul Asay has covered religion for The Washington Post, Christianity Today, Beliefnet.com and The (Colorado Springs) Gazette. He writes about culture for Plugged In and wrote the Batman book God on the Streets of Gotham (Tyndale). He lives in Colorado Springs with wife, Wendy, and his two children. Follow him on Twitter.