Why Napping Can't Replace a Good Night's Rest

Sleeping in spurts has the appeal of productivity, but inevitably you’ll collapse in your morning oatmeal.

Nap time! (Eduardo Munoz / Reuters)

Eight hours of uninterrupted sleep per night—it’s so widely recommended it approaches an axiom. The strange thing is, there’s nothing natural about it. In a landmark 1992 study, Thomas Wehr demonstrated that humans, like many other animals, are naturally inclined to sleep in bouts, separated by periods of activity. Given 10 hours per day of light, instead of the modern sixteen hours of artificial lights-on time, subjects sleep in two symmetrical blocks of several hours each. In the middle of the night, they wake up fully for up to three hours.

In 2010, I gave a talk at TEDGlobal in which I described this alternative sleeping pattern as a candidate for our ancestral sleep schedule. Pre-industrial literature from Canterbury Tales to Wuthering Heights describes a “first sleep” (sometimes called “beauty sleep” or “dead sleep”) and a “second sleep” in early modern English society. And ever since that talk was translated into 39 languages and approached the two-million-view mark, I have been receiving emails from polyphasic sleepers—people who sleep in spurts around the clock.

There is a seemingly inexhaustible supply of people who want to experiment with their own sleep. With the rise of productivity culture, time is money, both in the literal sense and in a broader kind of experiential currency. Many resent the third of their lives lost to unconsciousness and wish to be present for more of it. Some of those people—overwhelmingly male, in late adolescence—try sleeping polyphasically, in bits. If naps can be refreshing, the logic goes, perhaps that’s all we really need.

Buckminster Fuller, who prefigured our current crop of MIT-dropout geniuses in twice being expelled from Harvard, was in some ways a lifelong adolescent male. He spent a couple of years following a “Dymaxion sleep schedule” in which he would work for several hours, nap briefly, then work again, around the clock. He marveled at his productivity within a 22-hour daily waking life.

Though Fuller’s rhythm was dictated by his fatigue levels, and so entailed flexibility, a movement struck up around polyphasic sleeping on rigid schedules. The unfortunately named “Uberman schedule” involves twenty-minute naps every four hours, while the “Everyman schedule” at least recognizes the need for a core sleep—albeit usually less than three hours, with naps in between. There is little interest among this crew in the two-phase sleep of our ancestors, presumably because it does not result in more time spent awake and, one senses, manically typing lines of code into a laptop.

Scientists have attempted to study the effects of such a schedule, but it is very difficult when the vast majority of one’s test subjects drop out within a few days from the sheer misery of life. If round-the-clock napping is healthy, it sure doesn’t feel like it. A word of warning to those adolescent males who haven’t finished growing: One robust finding is that the release of growth hormone is strongly suppressed during polyphasic sleep, and its timing goes haywire.

Diehard polyphasic sleepers reassure neophytes on internet message boards that after the first month or so, the body adjusts to the new schedule. Keep suffering through and you will enter the promised land, they say. Any grogginess after that is blamed on inevitable slip-ups, like collapsing into your morning oatmeal and blowing the whole schedule.

On the one hand, there is no such thing as full adjustment to sleeping out of sync with one’s circadian rhythms, the 24-hour cycle of bodily functioning that humans share with almost all life on a rotating planet. Lab rats die early if you put them on similar schedules. On the other hand, there is some twisted truth to polyphasic sleep being more efficient.

Severe sleep deprivation activates a “recovery sleep” whenever a person finally gets shuteye. In this state, the power of the slowest brainwaves is much stronger. In other words, exhaustion brings on deeper sleep, which is why catching up on a lost night of sleep does not require an hour-for-hour reckoning. Polyphasic sleep, then, becomes more efficient as exhaustion increases. During naps, the body makes a valiant effort to survive.

But most of the perceived adjustment to wacky sleep schedules—including the long waking hours of trainee doctors or truck drivers—consists of a dangerous lack of conscious access to our own cognitive functioning. Sleep is the most powerful cognitive enhancer we know of, and without it people are much more impaired than they realize. Just as a drinker emerging from the bar is not the best judge of his ability to drive, many of society’s four-hour sleepers should not be operating heavy machinery.

That’s not to say that sleeping in blocks is unhealthy. Following the biphasic (two-block) pattern of our ancestors is a fine idea if one can fit a day’s aspirations into ten daytime hours and a midnight anti-nap. Likewise, a siesta in the early afternoon fits with a natural dip in our body’s arousal levels. As long as there are long stretches where sleep cycles can proceed undisturbed, the brain will awaken ready to learn again.

Many of us don’t have that luxury. Just a couple of weeks ago, Elon Musk tweeted that after working on the latest model of the Tesla car, he was “aiming to pull an all-nighter and complete the master product plan.” If your life looks like that, naps can play an important role. They commonly serve as catch-up sessions after a short night’s sleep, but they are actually much more effective if used prophylactically; that is, rather than conking out the morning after, try napping before an expected late night. The extra minutes will more than pay for themselves in added stamina.

Sleep fulfills important biological functions, particularly in the brain but also elsewhere in the body. With further research, we may one day curtail the need for sleep, condensing it so that people who would like to sleep less could still be fully refreshed. Our waking lifespan could be extended dramatically. But as in so many issues of biology, this cannot be achieved by willpower alone. The need for shuteye cannot be overcome by refusing to sleep.