12 Health Mysteries Explained

Why Do Teens Sleep Late?

They’re not lazy; they can’t help it. During childhood, melatonin, the hormone that regulates the wake-sleep cycle, is secreted by the pineal gland early in the evening. When puberty hits, from around ages 10 to 14, melatonin is released later, around 9 p.m. or 10 p.m. “This shift often makes many teenagers incapable of falling asleep before 11 at night,” says teen sleep expert Mary A. Carskadon, Ph.D., a professor at Brown Medical School and the director of the Bradley Hospital Sleep and Chronobiology Research Laboratory, in Providence. “Since teens still need about nine or more hours of sleep, they try to make up for the time they’ve lost at night by sleeping in.”