The stigma against napping is finally starting to wane — and for good reason. Taking a timeout to sleep during the day does much more than just give us a quick energy boost. It also confers some serious cognitive and health advantages as well. Here's what the latest science tells us.
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Unlike 85% of all mammalian species, humans sleep just once a day. Scientists aren't sure if we're naturally monophasic (as opposed to polyphasic) or if it's modern society that has made us so. Regardless, it's clear that we're not getting enough sleep. Nearly a third of us say we're simply not getting enough of it.
Power naps can alleviate our so-called sleep deficits, but they can also boost our brains, including improvements to creative problem solving, verbal memory, perceptual learning, object learning, and statistical learning. They help us with maths, logical reasoning, our reaction times, and symbol recognition. Naps improve our mood and feelings of sleepiness and fatigue. Not only that, napping is good for our heart, blood pressure, stress levels, and surprisingly, even weight management.
Now, before we get into the science behind many of these benefits, it's important to define what we mean by a power nap — and how to do it right.
Different types of naps
A power nap is a sleep session that happens during the day (ideally between 1:00 to 4:00 PM) lasting between 10 and 30 minutes. Any longer and you run the risk of developing "sleep inertia" — that unpleasant groggy feeling that takes a considerable amount of time to shake off. And naps later than 4:00 PM can disrupt your regular nighttime sleep.
But these aren't hard-and-fast rules. Some sleep scientists, like the University of California, Riverside's Sara Mednick — author of Take a Nap! Change your Life — says that naps at different durations result in different benefits. For example, a 10 to 20 minute nap will provide a quick boost of alertness while mitigating the onset of sleep inertia. At the same time, she's not a huge fan of the 30 minute nap, saying that recovery often takes too long.
Interestingly, research has shown that six-minute naps, known as ultra-short sleep episodes, can improve declarative memory (i.e. a type of long-term memory that pertains to our ability to recall facts and knowledge).
Mednick also makes the case for 60 minute naps, which are also good for cognitive memory processing. But to understand why this is the case, we need to look at how sleep cycles work.
While we're asleep, the brain cycles through a pattern lasting about 90 to 120 minutes. These stages include non-rapid eye movement (NREM) and rapid eye movement (REM) (which is associated with dreaming). During NREM sleep we enter into slow-wave sleep, which is the deepest kind. Slow-wave sleep helps us remember facts, places, and faces, which is why the 60 minute nap helps us in this regard.
There's also the 90 minute nap (but seriously, who has that much time during the day?). That's one complete sleep cycle. Mednick says these epic naps can aid in creativity and emotional and procedural memory, while resulting in a minimal amount of sleep inertia.
Check out Sara Mednick's TEDxYCRSalon talk:
Naps themselves can be broken down into four types:
- Planned napping: Also known as preemptive napping, it involves taking a nap before you get sleepy. It's a good thing to do if you know you're going to have a late night.
- Emergency napping: This is exactly as it sounds — taking a nap when you're so sleepy that you can't properly engage in your current activity. This is the kind of nap that's advisable to take when you get sleepy behind the wheel or while operating dangerous machinery.
- Habitual napping: This is the practice of taking a nap at the same time every day.
- Appetitive napping: The act of napping strictly for enjoyment.
Immediate Cognitive Benefits
As noted, napping is particularly great for alertness, learning, memory, and performance — and we've known this now for several decades.
A groundbreaking NASA study from 1995 (pdf) looked at the beneficial effects of napping on 747 pilots. Each participant was allowed to nap for 40 minutes during the day, sleeping on average for 25.8 minutes (which is just about right). Nappers "demonstrated vigilance performance improvements from 16% in median reaction time to 34% in lapses compared to the No-Rest Group."
Indeed, napping while on the job is not a bad idea. Planned naps have been shown to improve alertness and performance in emergency department physicians and nurses, along with first-year medical students. What these and other studies are showing is that naps can restore our attention, the quality of our work, while also helping us reduce our mistakes. It also improves our ability to learn while on the job. What's more, the effects of napping extend a few hours into the day.
Thankfully, companies are starting to catch on. Modern firms are increasingly creating sleep spaces while providing an encouraging, supportive environment. They're also setting up the right equipment for sleeping on the job; Christopher Lindholst of MetroNaps has installed specially designed sleeping pods for Google, Huffington Post, the Arizona Diamondbacks baseball teams, and other firms.
Think that grabbing a cup of coffee in the middle of the afternoon does just as well? Think again.
A 2008 study showed that naps are better than caffeine when it comes to improving verbal memory, motor skills, and perceptual learning. Afternoon naps improved free recall memory compared to the caffeine group after both 20 minutes and seven hour intervals, while resulting in improved learning on physical tasks than caffeine. It should be noted, however, that the researchers had their participants nap between 60 and 90 minutes. A cup of joe might be a tad more efficient. But as noted in the study, caffeine has been known to impair motor sequence learning and declarative verbal memory.
Other Health Benefits
Naps can also reduce stress, which is not a small thing as far as our overall health is concerned.
For example, napping can help us manage our blood pressure. Daytime sleep can confer heart-related benefits by accelerating cardiovascular recovery after bouts of psychological stress. Researchers discovered that a 45 minute nap literally lowers blood pressure.
An extensive 2007 study came to a related conclusion. For over six years, a research team tracked 23,681 people in Greece, none of whom suffered from coronary heart disease, stroke, or cancer. People who napped at least three times per week for an average of 30 minutes a day had a 37% lower chance of dying from a heart-related disease. This held particularly true for working men (too few women died to draw any meaningful conclusions).
And according to a letter published in the British Journal of Nutrition, obesity prevention may be as simple as turning off the television and having a nap. The authors write:
Like TV watching, sleep is an activity characterised by prolonged periods of reduced energy expenditure. Yet accumulating evidence suggests that adequate sleep protects against obesity, while short sleep duration is prospectively associated with increases in both total and abdominal adiposity in adults and children. These contrasting lines of evidence suggest that if an individual is planning to spend an afternoon on the couch, they are better off asleep than watching TV. While the above may seem like an odd public health message, it is nonetheless supported by a growing body of research suggesting that TV viewing and sleep have contrasting effects on energy balance and weight maintenance
Don't forget the children
Lastly, it should be noted that napping is good for people of all ages, but particularly children. Sadly, however, they're napping less and less.
After small children graduate from toddlerhood, they typically transition from biphasic (twice a day) to monophasic sleep (once a day). Some of this has to do with the children themselves, who are always on the go and reluctant to go down for nap. But it's also societal problem. And in fact, because there's a lack of science on the matter, some jurisdictions are looking to eliminate the preschool nap citing increasing curriculum demands (yes, really).
But according to a brand new study conducted by Rebecca Spencer, daytime sleep is critical for effective learning in young children. Classroom naps boosts the learning capabilities of preschool children by enhancing the memories they acquired earlier in the day. Conversely, children experience deficits in performance when they're nap-deprived — deficits that cannot be recovered during subsequence overnight sleep. The researchers conclude by saying that, "distributed sleep is critical in early learning; when short-term memory stores are limited, memory consolidation must take place frequently." Moreover, naps help children of all ages.
Other studies have reached similar conclusions. Naps help infants learn the rules of abstract language and when storing long-term memory. And to virtually no parent's surprise, sleep-deprived children between the ages of 2 and 3 "show more anxiety, less joy and interest and a poorer understanding of how to solve problems…"
Thankfully, napping is starting to catch on. Estimates vary, but surveys show that the frequency of napping (at least once a week) ranges from 36% to 80%. A recent "Sleep in America" poll showed that 46% of respondents napped at least twice in the last month, with an average nap duration lasting about one hour.
Additional reporting by Joseph Bennington-Castro.