• Jay Trisko

Why Napping Is Good for You, According to Science

Emerging evidence suggests a daytime snooze has powerful health benefits

Maya Kroth https://elemental.medium.com/why-napping-is-good-for-you-according-to-science-f4bddd4016b3

As long as there’s been civilization, there’s been disagreement about the value of a nap. Plato viewed sleep as anti-social, writing that “a sleeper is of no more use than one who is dead.” Rabbis debated the topic in the Talmud, concluding that napping should be avoided most of the time. “It is forbidden for a man to sleep by day more than the sleep of a horse,” commentators wrote. “And what is the sleep of a horse? Sixty respirations,” or about half an hour. By the Middle Ages, some physicians worried that midday naps caused fevers, headaches, dropsy (edema), and gout, especially if taken after a heavy meal.

Science has come a long way since then, but sleep — and napping in particular — is still surprisingly understudied. However, the evidence that is available points to napping as something of a magic pill that not only makes you more alert but also protects your heart, lowers your blood pressure, improves your memory, and enhances creativity. As leading sleep researcher Sara Mednick details in her book, Take a Nap! Change Your Life, napping also mitigates some of the most harmful impacts of sleep deprivation — suggesting that if we all napped on the daily, our roads would be safer, our bank accounts fatter, our sex lives better, and the bags under our eyes a little less noticeable.

Here are some of the most interesting findings from nap science.

Napping is biological

“All humans, irrespective of culture or geographical location, have a genetically hardwired dip in alertness that occurs in the midafternoon hours,” writes UC Berkeley neuroscience professor Matthew Walker in his 2017 bestseller, Why We Sleep.

Today, most people in the developed world sleep monophasically — that is, in one long stretch of nighttime sleep. But is that what nature intended? To investigate that question, anthropologists have observed preindustrial societies, such as the San people of the Kalahari Desert, whose lifestyles have remained relatively unchanged for millennia. The researchers found that most members of these tribes sleep in a biphasic pattern, getting seven to eight hours of shut-eye at night and taking a 30 to 60 minute nap in the afternoon, especially during hot weather. As for everyone else, factors as varied as the agricultural revolution, industrialization, and the invention of the lightbulb have all conspired to break the ancestral habit of sleeping twice a day. Today, more than a third of Americans get less than the recommended seven to nine hours of sleep a day, a 2016 CDC report found; the figures are worse for Brits, nearly three quarters of whom are underslept, according to The Sleep Council, a U.K.-based advisory group.

Napping may stave off heart disease

When Greece started phasing out its siesta in the 1990s, and keeping stores open longer during the day, researchers from Harvard University’s School of Public Health attempted to quantify the impacts of this cultural change. Walker writes that the results of the six-year study of more than 23,000 Greek adults were literally heartbreaking. Though none of the participants had a history of heart disease or stroke when the study began, by the end of the six-year period, those who had stopped taking their regular siesta suffered a 37% increased risk of death from heart disease compared to those who didn’t.

“When we are cleaved from the innate practice of biphasic sleep, our lives are shortened,” Walker says. “It is perhaps unsurprising that in the small enclaves of Greece where siestas still remain intact, such as the island of Ikaria, men are nearly four times as likely to reach the age of 90 as American males.”

Napping lowers your blood pressure — and could prevent heart attacks

About half of all Americans have high blood pressure, and they spend more than $100 billion per year on medication and other outpatient services to keep it under control. But findings presented at this spring’s American College of Cardiology conference found that a simple nap could be as effective as some pills when it comes to fighting hypertension.

Blood pressure is measured in millimeters of mercury, or mm Hg, and when you take a low-dose hypertension drug, you can expect to see your reading go down by an average of 5 to 7 mm Hg. A nap, by comparison, is associated with a similarly impactful drop of an average 5 mm Hg, making it at least as effective as cutting out salt and alcohol from your diet.

“These findings are important because a drop in blood pressure as small as 2 mm Hg can reduce the risk of cardiovascular events such as heart attack by up to 10%,” the study’s author, Greek cardiologist Manolis Kallistratos, noted. “Based on our findings, if someone has the luxury to take a nap during the day, it may also have benefits for high blood pressure. Napping can be easily adopted and typically doesn’t cost anything.”

“Nighttime sleep and daytime siesta are governed by distinct mechanisms and serve separate functions for health and survival.”

Napping helps you remember — and forget

Sleep helps the brain process information gathered throughout the day and actually helps restore the brain’s ability to learn. To test this, Walker and his colleagues had study participants complete a short-term memory challenge — matching 100 pairs of faces and names — at noon. Then they asked one group to take a 90-minute nap, while the other group played board games or surfed the internet. At 6 p.m., both groups did another learning activity. The non-nappers had a much harder time learning new facts during the second test, lagging behind the napping group by 20%.

To find out why, the researchers analyzed the brainwaves of the nappers. They discovered that every 100 to 200 milliseconds, the nappers’ brains sent loops of electrical current from the hippocampus, which houses short-term memories, to the cortex, where long-term memories are kept. They were actually watching memories move from short-term to long-term storage, freeing up space in the nappers’ hippocampus that could then be used to learn more facts in the second learning session.

Then they devised another study, to test whether sleep’s memory-consolidation function could discriminate between which facts to remember and which to forget. They had research subjects study a long list of words and directed them to remember some words and forget others. Those who napped remembered the words they were told to remember and seemed to have avoided remembering the others; the non-napping group did not show any such difference.

“Sleep does not offer a general, nonspecific preservation of all the information you learn during the day,” Walker concludes. “Instead, sleep is able to offer a far more discerning hand in memory improvement: one that preferentially picks and chooses what information is, and is not, ultimately strengthened.”

Napping may even help you learn information you haven’t consciously perceived, a 2018 study found. Researchers at the University of Bristol gave subjects a “masked prime task” — sort of like a subliminal message — and a control task, then had them take a 90-minute nap and complete the tasks again. After sleep, they found that participants’ brains still processed the hidden information even though the owners of those brains weren’t conscious of having taken it in.

There may be an actual napping gene

In 2017, researchers in Spain studied the siesta habits of 53 pairs of female twins to determine the impact of genetic factors on sleep rhythms, including napping. Study participants wore an actigraphy monitor on their wrists for a week (thought to be a more objective way of measuring sleep than having people self-report on questionnaires); about 60% took a nap at least once during that week, sleeping for an average of 45 minutes.

The data suggested that the level of sleepiness people felt after lunch and the subsequent need to take a nap may be genetically influenced, even after controlling for other factors like how much sleep each twin got the night before. Genes may also have an impact on when the sleepiness comes on, how long naps last, and the overall “robustness” of the sleep rhythm.

Like humans, Drosophila flies are also genetically wired for a daytime nap — except when they’re not. This year, researchers at Rutgers’ Center for Advanced Biotechnology and Medicine found a gene that suppresses the flies’ tendency to take a nap when the weather is cool, which they dubbed “daywake.” Hot days are more dangerous for the flies, so an afternoon siesta protects them from heat exposure, but on cooler days when that risk is presumably lower, the daywake gene gives the flies the flexibility to stay awake and do something productive instead.

“Although the daywake gene is not present in humans, our finding reinforces the idea that nighttime sleep and daytime siesta are governed by distinct mechanisms and serve separate functions for health and survival,” Edery said in a statement.

A 2018 study conducted at Japan’s University of Tsukuba also probed the genetics of daytime sleepiness, this time in mice. Researchers found that a single amino acid plays a vital role in regulating “sleep need,” and by mutating a single gene, they could manipulate how sleepy the mice got and how long they napped for. They think the findings might eventually shed light on the causes of idiopathic hypersomnia, a sleep disorder whose sufferers can never get enough sleep, no matter how many naps they take or how many hours they sleep per night.

Almost everything, from surgery to driving, becomes more dangerous at “nap time”

The effects of not taking a nap when you hit the circadian trough can be downright terrifying. In his book When: The Scientific Secrets of Perfect Timing, author Daniel Pink outlines the myriad ways: Danish schoolchildren score worse on tests when they take them in the afternoon, judges are less likely to issue prisoners a favorable ruling, anaesthesiologists are three times more likely to give patients a fatal dose of anesthesia, and nurses are 10% less likely to wash their hands. People behave more unethically in the afternoon, too, and sleep-related traffic accidents spike between 2 p.m. and 4 p.m. It all seems to point in one direction: Just take a nap already.

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