Feeling drowsy? You could pour a cup of coffee or take a brisk walk, but there is a cozier alternative: the nap. Daytime dozing is becoming a workplace trend. Ben & Jerry's, Zappos, Uber and Google have installed dedicated nap spaces in their headquarters, in hopes that some midday shuteye will boost employee productivity and creativity. While company nap rooms might still be an exception rather than a rule, a sizeable fraction of Americans still find a way to squeeze in a nap. According to a 2009 report by the Pew Research Center, a third of U.S. adults nap on any given day.
For people who don't catch enough Zs during the night, daytime naps can improve alertness and motor performance. "Everybody agrees that if you are sleep deprived, you can't learn, perform or think very well," says Jerome Siegel, PhD, director of the Center for Sleep Research at the University of California, Los Angeles.
But for healthy adults who do get a reasonable amount of nighttime sleep, is there any benefit to a midday nap? Signs point to yes, says Kimberly A. Cote, PhD, a psychology professor at Brock University in Ontario. While little work has been done to look at the long-term effects of habitual napping, studies point to a variety of immediate benefits following an afternoon nap. "If you're talking about a healthy adult population, I think just about anyone could benefit from a nap," she says.
Sleep and learning
Even in well-rested people, naps can improve performance in areas such as reaction time, logical reasoning and symbol recognition, as Cote described in a 2009 review (Journal of Sleep Research, 2009). They can also be good for one's mood.
A study by University of Michigan doctoral student Jennifer Goldschmied and colleagues found that after waking from a 60-minute midday nap, people were less impulsive and had greater tolerance for frustration than people who watched an hourlong nature documentary instead of sleeping (Personality and Individual Differences, 2015). "Frustration tolerance is one facet of emotion regulation," says Goldschmied. "I suspect sleeping gives us more distance [from an emotional event] — it's not just about the passing of time."
Researchers are only just starting to understand how naps might affect emotion regulation, Goldschmied adds. But the benefits of napping for memory and learning are well described. "Even a brief bit of sleep helps reinforce learned material," she says.
For many types of memory, the benefits of a nap are substantial, says Sara Mednick, PhD, a psychologist at the University of California, Riverside. Take perceptual learning. Previous research demonstrated that people perform better on a visual texture-distinguishing task after a night of sleep than they do immediately after learning it. Further, Mednick and colleagues found people performed just as well on the test after a 60- to 90-minute nap as they did after a full night of slumber (Nature Neuroscience, 2003).
"What's amazing is that in a 90-minute nap, you can get the same [learning] benefits as an eight-hour sleep period," Mednick says. "And actually, the nap is having an additive benefit on top of a good night of sleep."
In another experiment, Mednick found that an afternoon nap was about equal to a dose of caffeine for improving perceptual learning. But in other ways, a midday doze might trump your afternoon latte. She found people who napped performed better on a verbal word-recall task an hour after waking compared with people who took caffeine or a placebo (Behavioural Brain Research, 2008). While caffeine enhances alertness and attention, naps boost those abilities in addition to enhancing some forms of memory consolidation, Mednick notes.
A catnap can benefit performance in a variety of other memory domains as well. In one recent example, Axel Mecklinger, PhD, at Saarland University in Germany, and colleagues studied memory recall in volunteers who learned single words as well as meaningless word pairs (such as "milk-taxi"). Half of the participants then took a 90-minute nap, while the others watched a DVD. Then the researchers retested participants' recall.
Both groups remembered about the same number of single words. This was a test of so-called item memory — the type of memory you use when you recall a grocery list. But the nappers remembered significantly more of the word pairs. This type of "associative memory" is involved in remembering things that are linked, such as putting a name with a face. And unlike item memory, the hippocampus plays a strong role in associative memory, suggesting that naps benefit hippocampus-dependent learning (Neurobiology of Learning and Memory, 2015).
Other research builds the case that the hippocampus benefits from a nap. Matthew Walker, PhD, a professor of psychology at the University of California, Berkeley, and colleagues recruited volunteers to tax their associative memories by learning a long list of name-face pairings.
Half the participants then took 90-minute midday naps. That evening, the participants were given a new round of learning exercises with novel pairings. Those who hadn't napped didn't perform as well on the evening test as they had in the morning. But the nappers did better on the later test, suggesting the sleep had boosted their capacity for learning (Current Biology, 2011).
Adaptive behavior
Not all the nap research is so glowing, however. Some studies have suggested that excessive sleep and daytime naps are associated with higher levels of C-reactive protein, a marker for systemic inflammation (which has been linked to a host of ills, including cancer, diabetes, depression and heart disease). Yet other research suggests naps can improve immune function. Indeed, a review by Rebecca Spencer, PhD, found the picture is almost comically muddy: Various studies in various populations have found that too much sleep, too little sleep, frequent naps and infrequent naps can all be linked to elevated C-reactive protein. Ultimately, more work needs to be done to understand what patterns of nighttime and daytime sleep are healthy, and for whom (Sleep Medicine, 2015).
Other concerns about the downside of naps are better established. The biggest concern is that daytime sleep can disrupt nighttime sleep. Sleeping too much during the day can interfere with the ability to fall asleep and stay asleep at night. That's why, says Siegel, "one of the standard instructions at sleep disorder centers is to tell people not to nap."
Siegel admits he's never been a napper himself. His research suggests he's hardly alone in that respect. In a recent study, he and his colleagues tracked the sleep patterns of hunter-gatherer groups in Tanzania, Namibia and Bolivia. These people are thought to live much like our ancestors did some 10,000 years ago. And while nearly all of them took a break from the sun during the heat of midday, none of the 94 individuals they followed took regular naps.
"I'm not saying we should do everything our ancestors did, but it suggests that napping is not a part of the ancient human physiology," Siegel says.
Still, just because Siegel's subjects didn't nap doesn't mean naps have no benefit, says Cote. "Sleep is a behavior, and human behavior is highly adaptable," she says. "We get sleep in many ways. After a certain age, naps are not biologically necessary, but napping does have benefits."
It's likely that some people benefit more than others, though. "A certain percentage of people are regular nappers. If you ask these people, they'll be aware they're getting benefit: They're more alert, have better moods and they're feeling sharper," Cote says.
But others — including Cote — wake up groggy after naps and drag the rest of the day. She believes people who choose to nap regularly are predisposed to get more out of it. Some of her own laboratory research suggests that frequent nappers show greater improvements in performance following a midday nap than people who don't often nap (Biological Psychology, 2006). "I think we self-select this behavior," she says.
Other research is starting to piece together clues about who benefits from naps, and why. In not-yet-published research, Goldschmied and colleagues found evidence that people who self-identify as night owls tend to show bigger improvements in performance following a nap, compared with their early-bird counterparts.
The way you move through the stages of the sleep cycle may also play an important part in whether you're a born napper or not. Mednick (who loves a nap when she can get it) says people who nap regularly appear to stay in lighter stages of sleep that they can wake from easily, while infrequent nappers often sink into deeper sleep and wake up woozy. "It appears there's a qualitative difference to naps," she says.