How teenagers' lack of sleep is harming their mental health

Research has found that teenagers should be getting eight to ten hours of sleep every night. But many are sleeping far less than that and nearly one in four also suffer from insomnia. William Brangham reports on why it's so hard for so many teens to sleep, and why it's taking a toll on their mental health. It’s part of our ongoing series, Early Warnings: America’s Youth Mental Health Crisis.