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Feature Article

Sleep researchers home in on the benefits of napping

Getting a good night's sleep is important for everyone. Good sleep refreshes people, helps them perform better, and contributes significantly to health and happiness. For many Veterans, however, getting a good night's sleep is extremely difficult.

Sleep disturbances are common in patients suffering from bipolar disorder, substance abuse, major depression, panic disorder, and chronic pain disorders. Sleep disorders following recent exposure to traumatic events can predict the later development of posttraumatic stress disorder (PTSD).

Disrupted sleep, or the inability to get a full night's sleep without interruption, is a very common negative consequence of PTSD. According to VA's National Center for PTSD, nightmares are one of the 17 symptoms of the disorder, and as many 71 percent of those with the illness reported experiencing nightmares, sometimes or more frequently, compared to only 3 percent of those who did not serve.i

For some who simply cannot get a good night's sleep, there is a way to avoid many of the consequences of sleeplessness. "Napping has been shown to alleviate the negative physical and psychological symptoms of disrupted sleep," says Elizabeth A. McDevitt, a graduate student in the department of psychology at the University of California, Riverside. At the time the research was conducted, McDevitt was affiliated with the San Diego VA Medical Center and the University of California, San Diego (UCSD).

According to a study recently published online in the Journal of Physiology and Behavior by McDevitt and two colleagues from the San Diego VA and UCSD,ii napping is especially helpful to manage circadian disruption (problems related either from changes in a persons sleep-wake cycle, such as jet lag, daylight saving time, or between workweeks and weekends; or through the inability to get enough sleep in the time allotted for sleep.) In healthy, well-rested subjects, napping has also been shown to improve performance across a range of performance tasks.

Despite the benefits of napping, however, some people report that they simply cannot nap, or don't want to nap. In their study, McDevitt and her colleagues set out to determine why some people nap and others do not.

She and her colleagues asked 27 healthy, non-smoking college students between the ages of 18 and 35 to participate in an experiment. All of them spent between seven and nine hours in bed every night, and none of them had a sleep disorder. They were asked to keep a diary of their sleep habits for a week, including their daily naps if they took them, and wore special actigraph wristwatches (small, wristwatch shaped devices that record motion and are used to assess sleep by determining whether a person is active or inactive) to verify what they had put down in their diaries.

After a week of measurements, each participant reported to the Laboratory for Sleep and Behavioral Neuroscience at the San Diego VA. Their level of sleepiness was measured at 9 a.m., 11 a.m., 4:30 p.m., and 6:30 p.m. At 1:30 p.m., they were all asked to take a nap, and were allowed to sleep for a maximum of 90 minutes—but they were given no more than 120 minutes in bed, whether they napped or not. While they napped, their brain waves were monitored through electrodes to see how deeply they were sleeping.

By correlating the information in the subjects' diaries, and analyzing the brain wave information they obtained, the team found that people who nap frequently sleep more lightly during their naps than those who usually never nap at all. In sleeping, the body progresses through a series of five stages, from light sleep through dreaming, called the sleep cycle. (Sleep does not progress through these stages in order, however.)

Those who had taken three to four naps in the week before the brain wave tests took place had the least amount of slow wave sleep (scientist's term for stage 3, or deep sleep) and the most amount of stage 1, or light sleep; those who took one to two naps a week had the most amount of stage 2 sleep, which is somewhat deeper, and those who never napped at all had the highest amount of stage 3 sleep while in the laboratory, meaning they slept the most deeply. The naps that people of all groups took did not measurably affect their sleep at night.

Using this data, the team developed two hypotheses. First, that some people avoid napping because of the high levels of deep sleep that they fall into when they do nap—meaning that, when they wake up, they feel groggy and tired instead of rested and refreshed. And second, people who choose to nap may just be sleepier people than those who do not.

"Individuals who frequently nap may generally be sleepier people who are self-treating their sleepiness with daytime naps," said McDevitt. "They might be predisposed to be good daytime nappers, or they have learned to become skilled nappers through practice."

The team suggested that future studies should consider the possibility of nap practice or nap training to maximize the benefits of napping, and examine how differences in sleep associated with nap behavior may influence changes in performance following a nap.

ii EA McDevitt, WA Alaynick, SC Mednick, "The effect of nap frequency on daytime sleep architecture," Physiol Behav, 2012 May 31 (epub ahead of print.) doi: 10.1016/j.physbeh.2012.05.021.

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