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May 11, 2015 4:58 PM EDT

The medical community doesn’t fully understand why, but there’s something about puberty that throws kids’ systems out of whack. It’s as if teenage bodies switch over to daylight savings time, a condition sometimes known in the medical community as a “phase delay.” They begin to have trouble falling asleep early and then, of course, want to sleep in the morning for as long as possible. While teenagers may not need as much sleep as they did when they were children, their growing bodies still get pretty fatigued; they just don’t feel it until about two hours later.

“Why this happens nobody has a clue—hormone changes are a good bet,” says Dr. David Gozal, a pediatric sleep expert at the University of Chicago. “Paradoxically, this period of puberty is associated with an increased need for more and longer sleep. So now they’re in conflict with the sleep schedules of our society.”

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