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gaz_02Psychology professor David Dinges is an unlikely space commander. But the chief of the Perelman School of Medicine’s sleep and chronobiology division recently oversaw a six-person multinational crew on a 17-month mission to Mars. Sort of. Along with colleague Mathias Basner, an assistant professor of sleep and chronobiology in psychiatry, Dinges led an experiment on six surrogate astronauts confined to a “spaceship-like habitat” for 520 days.

Monitoring the effects of simulated space travel on sleep and performance, the researchers delved into a host of disturbances that afflicted the subjects’ sleep schedules, sleep quality, and overall levels of lethargy.

Broadly speaking, the study’s results—published in January in the Proceedings of the National Academy of Science—mainly served to underscore what Dinges has been saying about sleep for some time now.

“Americans pride themselves on going with less sleep,” he says, “which they like to brag about. But most of that braggadocio is inaccurate. They’re actually suffering the consequences.”

While many of his countrymen burn the midnight oil and turn up their noses at daytime nappers, Dinges contends that time spent sleeping is time well spent—and not just for astronauts. Recently he spoke to Gazette contributor Liz Slivjak C’13 about some of the reasons why.

Is there really an optimal number of hours of sleep per night for all adults? Can this number vary among the population?

Adults will typically sleep seven to eight hours a night, for the vast majority of the population. There’s a small percentage of people—maybe less than 5 percent—who sleep less than six hours a night and can get by on that, meaning they’re fully alert and they don’t suffer any consequences. But the majority of adults who get less than seven hours sleep suffer from the effects of that sleep loss. In other words, they say they’re getting by on it, but in fact they’re not really avoiding the consequences of the sleep loss for safety and health … They can’t stay awake in meetings, they fall asleep driving, or they’re irritable from inadequate sleep, or they’re eating too much or craving high-fat foods because they haven’t had enough sleep.

Is there any harm in losing a couple of hours of sleep a few nights during the work week and then making up those hours over the course of the weekend?

In fact you pay a price for it, because inadequate sleep chronically accumulates. So let’s say you biologically need eight hours a night to be fully alert. If you get an hour less than that every night, then you tend to want to oversleep on the weekends. And that’s a sign that you’re chronically partially sleep-deprived. If you do that day after day, you build up a sleep debt. And that sleep debt produces elevated levels of sleepiness, problems with sustained attention, problems with remembering, etc.

Does it matter whether the seven-to-eight hours of sleep are consecutive? Would it be OK to sleep six hours at night and then nap for two hours during the day?

This is a good question, and one that we tried to answer with two very large experiments for the National Space Biomedical Research Institute and NASA, where we put people under chronic conditions of sleep of different amounts per day. Some of them got the full seven-to-eight hours at night. But most of the other 70 conditions we studied had some sleep at night—like four, five, or six hours—and then a supplemental nap in the daytime of 20 minutes, 40 minutes, 60 minutes, or an hour and a half. We also repeated those experiments but put the long sleep in the daytime and the nap at night—and that’s actually very problematic, because of problems with the circadian system, which wants us to sleep at night. But the result of all the experiments was that the total amount of sleep you get per day is the critical factor. The bottom line is, it’s perfectly OK to split your sleep up by getting short sleep at night and then adding a nap during the daytime.

Are some people better at napping than others? Are there natural nappers?

About a quarter of the population feel that they don’t want to nap, either because they can’t nap, or more often because they don’t like the grogginess they feel when they awaken. That’s called sleep inertia—although that is easily overcome by physical activity: putting water on your face, walking around, drinking coffee. Another 25 percent enjoy napping every day. They like it, and they’re not bothered by the inertia of awakening in the day from sleep. And then the remainder, the other 50 percent of the population, we call replacement nappers. They’re people who got up early, had shortened sleep, so they take the nap to compensate for that and to get their sleep total for the day back up closer to seven hours. So you’ve got really three sorts of attitudes towards napping.

Is it possible to train your body to avoid the effects of sleep inertia rather than just simply treating its symptoms?

Not that anybody has found. There’s one way to reduce it: if you can awaken from rapid-eye-movement sleep, which is the sleep where we’re most aware of our dreams—where we have visual imagery—there’s less sleep inertia there. But even that’s not guaranteed.

How serious is not getting enough sleep?

There is a large body of scientific evidence to suggest that the single most effective daily enhancer of our performance, our moods, motivations, and ability to do things safely and effectively—as well as control our appetites, particularly food intake—is appropriately timed and appropriate duration sleep.

So if there’s one thing you want to make sure you do during a period of intense work and study, get your sleep.

If you pay attention to sleep in a competitive environment, you can actually use sleep to your advantage to perform better, because sleep has a key role in memory consolidation of material that you learned. It also helps with immune responses. If you get vaccinated, you’ll have a better vaccine coverage, the studies suggest, if you’ve had adequate sleep as opposed to being sleep-deprived. And there are recent studies coming out [that suggest] you’ll read emotions better, and display emotions better. And you’ll look better—there are new studies now appearing that claim that once you’re no longer sleep-deprived, your face looks better. The morphology of the face, the color of the skin looks better. This is something people have believed for a long time but there hasn’t been much data.

So whatever the full range of effects is, there’s no question they’re all positive from getting sleep. There’s no downside.

Do you have any recommendations for adults trying to get more sleep or a better night’s sleep?

You need a healthy sleep environment: quiet, cool, dark, etc. You need a regular schedule. Regular schedules really, really help. Try to go to bed at the same time, and get up at the same time. If you have to pull an all-nighter, you need to load up on sleep before you do it. And then do the work recognizing that, when you can, [you should take] power naps. The worst thing you can do is be partially sleep-deprived all week and then pull an all-nighter. You’re so inefficient, you don’t study well, you don’t learn well, you don’t remember well. It’s much better to front-load on your sleep.

Is there a certain amount of time before sleep when you should turn off all electronic devices?

Nobody has studied this. But because the screens are blue-light screens, and that can send a signal to the brain that can have an arousing effect, it’s probably better to shut all of that off at least a half-hour to an hour before you go to bed. Allow yourself that wind-down period. Not everybody needs it, but most people do. As adults, we tend to do something very similar to what we do with little children when we read them bedtime stories. We put them in a comfortable position. They’re lying in bed. We start to stimulate their imaginations, which stimulates the reverie of the brain. And the brain’s control over its thought processes lets go, and it goes to sleep. In a sense, that’s what we’re doing when we just relax in the evening—when we read a mystery or watch a light television program just before bed. Things like that—a little bit of humor, a little relaxation, calming activities—help a great deal before bed.

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