There’s an art to napping.
Studies have found different benefits—and detriments—to a nap’s timing, duration and even effect on different people, depending on one’s age and possibly genetics.
“Naps are actually more complicated than we realize,” said David Dinges, a sleep scientist at the University of Pennsylvania’s Perelman School of Medicine. “You have to be deliberative about when you’re going to nap, how long you’re going to nap and if you’re trying to use the nap relative to work or what you have coming up.”
A snooze on the couch on a Sunday afternoon may seem like the perfect way for a responsible adult to unplug. But at a time when roughly one-third of people report not getting enough sleep, more naps, albeit short ones, might make for a more functional workforce, researchers say.
Sleep experts break sleep down into several stages, which the brain cycles through roughly every 90 to 120 minutes. These stages are broadly characterized into non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. NREM is further broken down into stage one and two, which are considered light and intermediate sleep, followed by slow-wave sleep. Awakening from slow-wave sleep, the deepest kind, results in what doctors call sleep inertia or sleep drunkenness: that groggy feeling that can take awhile to shake off. Finally, there’s REM sleep, often associated with dreaming.
Sara Mednick, an assistant psychology professor at the University of California, Riverside, said the most useful nap depends on what the napper needs.
For a quick boost of alertness, experts say a 10-to-20-minute power nap is adequate for getting back to work in a pinch.
For cognitive memory processing, however, a 60-minute nap may do more good, Dr. Mednick said. Including slow-wave sleep helps with remembering facts, places and faces. The downside: some grogginess upon waking.
Finally, the 90-minute nap will likely involve a full cycle of sleep, which aids creativity and emotional and procedural memory, such as learning how to ride a bike. Waking up after REM sleep usually means a minimal amount of sleep inertia, Dr. Mednick said.
Experts say the ideal time to nap is generally between the hours of 1 p.m. and 4 p.m. Napping later in the day could interfere with nighttime sleep.
The body’s circadian rhythms help people to expect to be awake in the morning and early in the night. “So if you take naps when your brain doesn’t expect to be sleeping, you feel kind of thrown off,” contributing to the sleep inertia effect, said Rafael Pelayo, a clinical professor at Stanford University School of Medicine’s Sleep Medicine Center.
A telltale sign of being very sleep-deprived, he said, is dreaming during a short nap. “Definitely in a 20-minute nap you should not be dreaming,” he said.
Ilene Rosen, an associate professor of clinical medicine at Penn’s Perelman School of Medicine, said the ideal duration of a nap is still being debated, but generally speaking the “10-to-20-minute nap is really the optimal time in terms of bang for your buck.”
Leon Lack, a psychology professor at Flinders University in Australia, found in a 2006 study in the journal Sleep that among shorter breaks, 10-minute naps packed the most punch.
The study compared naps ranging from 30 seconds to 30 minutes, testing 24 participants at each of several intervals. After each nap the individuals were tested on a variety of mental-processing tasks. The sharpness of the 10-minute nappers became apparent “right away,” Dr. Lack said, and remained apparent for about two to 2 1/2 hours.
Those who took 20- and 30-minute naps tended to feel groggy immediately after the nap for up to about 30 minutes. From there, they showed mental sharpness similar to what researchers saw from the 10-minute nappers, with that sharpness lasting a bit longer.