How Many Hours of Sleep do You Actually Need?

How Many Hours of Sleep do You Actually Need?

Claire Maldarelli

From an evolutionary standpoint, sleep is quite literally a waste of your time, yet it’s fought its way through countless years of adaptation in nearly every living animal on Earth. So it must be important, right?

In fact, researchers have found that sleep plays a vital role in the functioning of nearly every organ system in the body. At the same time, medical conditions, a busy schedule, and even the simple unavoidable act of aging constantly challenge the number of hours we allow ourselves. But that begs the question: how much sleep do we actually need? And can we train ourselves to need less?

First, let's talk about that eight hour figure that gets tossed around. It’s far from some arbitrary number. It's truly the number of hours we naturally crave, and there are two pretty strong pieces of evidence for it. In a series of experiments, researchers took study participants into a laboratory with no sunlight or other visual cues and, at night, gave them a non-negotiable, nine-hour-long opportunity to sleep. They did this each night for a number of weeks, and the results were always the same: even when provided with more time, humans will typically spend an average of eight hours catching up on their Zzz.

And that wasn't the only study to support the eight-hour sleep schedule. Back in 1938, a sleep researcher named Nathaniel Kleitman and one of his students spent 32 days living in Mammoth Cave in Kentucky, one of the longest and deepest caves in the world—an environment completely void of sunlight. When they analyzed their sleep patterns, they found that they, too, slept about eight to eight and a half hours per night.

But what happens when we deprive ourselves, as many Americans do, of all or some of these recommended hours? It turns out, a lot...