Napping may not be such a no-no

Research is showing that the daytime snooze may have benefits and not interfere with nighttime sleep.

The nap has long been the troubled stepchild of the unassailably hygienic and universally admired good night's sleep. At work, if you get caught napping, it could get you into trouble or, more mildly, sully your reputation for diligence. In studies, naps have been linked to ill health, although usually as a consequence, not a cause. And in sleep recommendations, naps have taken a back seat — or been cast as a threat to nighttime sleep. On its Web site, the American Academy of Sleep Medicine tells people to "avoid taking naps if you can."

But lately, naps have been shedding some of their bad-for-you image. Researchers are finding benefits. A few employers have become accommodating of the quick snooze. And some research suggests that instead of fretting about napping more as we get older, we should plan on adding daytime sleep to our schedule as a way to make up for the normal, age-related decay in the quality of our nighttime sleep.

Getting over the hump

Naps, of course, can be an antidote to daytime sleepiness, and we get sleepy during the day for a wide variety of reasons. There is, in fact, a biological clock located in a cluster of cells in the hypothalamus of the brain. Those cells orchestrate the circadian (that is, daily) ups and downs of many physiological processes (body temperature, blood pressure, secretion of digestive juices), including sleep and wakefulness. As you might expect, the usual circadian pattern is wakefulness during the day followed by gradually increasing sleepiness in the evening, but it's also common to have a little "hump" of midafternoon sleepiness programmed into the circadian schedule. An afternoon nap is one way to accommodate that hump.

In 2008, British researchers reported results of a study that compared getting more nighttime sleep, taking a nap, and using caffeine as ways to cope with the afternoon hump. The nap was the most effective.

Another factor in daytime sleepiness is the number of hours you've been awake. After about 16 consecutive hours without sleep, most of us will start to feel tired. Ideally, this homeostatic sleep drive, as it is called, is in sync with the one set by our circadian rhythm, so they're mutually reinforcing. But if you work a night shift, or have problems sleeping at night, your 16-hour allotment of wakefulness may begin — and end — earlier, which can set you up for grogginess in the late afternoon or early evening. A short nap won't completely reset the timer, but it can buy you some time before the grogginess sets in again.

On the job

Since 2000 or so, researchers at Harvard and elsewhere have conducted dozens of experiments that have shown that sleep improves learning, memory, and creative thinking. In many cases, the edifying sleep has come in the form of a nap. For example, several studies have shown that if people are asked to memorize something — say, a list of words — and then take a nap, they'll remember more of it than they would have if they hadn't taken the nap. Even catnaps of six minutes (not counting the five minutes it takes to fall asleep on average) have been shown to make a difference in how well people retain information.

Robert Stickgold, a Harvard sleep researcher, says napping makes people more effective problem solvers. His research group has shown that taking a nap seems to help people separate important information from extraneous details. If the nap includes REM sleep — the phase during which dreaming occurs — people become better at making connections between seemingly unrelated words.

Stickgold says his and others' findings argue for employer policies that actively encourage napping, especially in today's knowledge-based economy. Some companies have set up nap rooms, and Google has "nap pods" that block out light and sound.

Understandably, employers are concerned about abuse: employees catching up on sleep they should be getting on their own time. But there may be a place for "strategic napping," especially among people who work a night shift. Results from a New Zealand study published in 2009 showed that air traffic controllers working the night shift scored better on tests of alertness and performance if they took advantage of a planned nap period of 40 minutes. Researchers in the Harvard Division of Sleep Medicine are working with fire departments to improve sleep policies. One of their recommendations is that firefighters on the night shift take a nap in the late afternoon before their shift starts.

Can be a sign of trouble

Daytime sleepiness, and napping to relieve it, can also be a sign of a health problem. Daytime sleepiness is one symptom of Parkinson's disease, for example. In studies of older people, regular napping has been associated with diabetes, depression, and chronic pain, presumably because those conditions adversely affect nighttime sleep. Indeed, it only stands to reason that napping might be a coping mechanism for those who can't sleep well at night, no matter the age or the reason. Sleep problems, daytime grogginess, fatigue, a desperate need to nap — all are noteworthy, and suitable topics of conversation with your doctor.

Bad nighttime sleep may be a cause of napping, but what's less clear is whether the reverse is true: does napping cause bad nighttime sleep? That's been the belief, but a couple of studies haven't found an association between napping and complaints about nocturnal sleep. In fact, a few studies have shown that napping, and the ability to nap, are more common in older adults who sleep well at night than in those who don't. And it's been suggested that a nap might be an appropriate adaptation for older people who, as a rule, sleep an hour less per night than younger people and wake up earlier.