I define sleep as a multifaceted process that happens every 24 hours and that should last seven to nine hours in adults and as long as nine and a half hours in adolescents. During sleep, consciousness is significantly reduced, we disconnect from our surroundings, and our bodies engage in restorative functions—making proteins, hormones, and neurotransmitters—that enable growth, learning, and mood stabilization. Basically, sleep affects every aspect of functioning. It heals the previous day’s stresses and strains—perhaps a pulled muscle or a cold—and gives us the mental and physical energy we need to function the next day—without being too grouchy. Sleep lets us—more likely, our teens!—run the 50-yard dash in the state track competition and allows us to think clearly and learn figures and facts. Adequate nighttime rest takes a body and mind that are worn out from their day and brings both back to a clean baseline.

Although sleep is a time during which we look quiet, there’s actually a great deal of metabolic, or physical and chemical, activity taking place. Much of that activity takes place in the brain. Years ago scientists believed that, because the body looked quiet, the brain was quiet too and was resting like the body. But with the invention of the electroencephalograph, which uses small metal cups glued to the scalp to record microvolts of brain wave, or EEG, activity, scientists learned that the brain, as well as the body, is hard at work while we sleep.

Sleep is critical to helping both the mind and the body maintain physical and psychological well-being. But more than 50 million Americans as well as millions of people around the world report difficulty sleeping. That means that many of us, including teens, are not living as well as we could.

How much sleep do we need to fuel our potential? I’ve already said that the ideal amount of sleep for adolescents is eight and a half to nine and a half hours. But it’s not much less for adults: seven to nine hours (in my practice I call seven hours the lowest legal limit of sleep). And babies and small children need tons of it. But needing it and getting it are two very different things.

The 24/7 society we live in, overloaded with electronic tools and all forms of entertainment, is a major reason we don’t get the sleep we

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