By Bahar Gholipour, Staff Writer

Published: 10/24/2013 10:50 AM EDT on LiveScience


A nap, a siesta, or as the Chinese call it, a wujiao, is a pleasant break from the day, but the debate on its health effects continues. While some studies have found cognitive benefits from a short afternoon sleep, others have suggested a link between napping and negative effects, including a shortened life span.


Now, a new study has found that people who nap longer than others are at higher risk for diabetes, suggesting that naps of different durations affect the body differently.


In the study, the researchers looked at 27,000 retired Chinese men and women, and categorized them into four groups based on their nap duration, ranging from zero minutes to more than 60 minutes.


More than two-thirds of the participants — about 18,500 people — reported regularly taking afternoon naps. After adjusting for confounding factors such as smoking, how long participants slept at night and physical activity, the results showed that those who reported napping for more than an hour had a higher risk of prediabetes and diabetes compared to "nonnappers." [7 Strange Facts About Insomnia[1] ]


While longer nap durations were associated with an increased risk for high blood sugar and diabetes, people who took short naps, of less than 30 minutes, tended to have lower blood-sugar levels compared to nonnappers; however, this link was not statistically significant.


"The findings may have important implications for people who regularly nap[2] ," said Eliane Lucassen, a researcher at Leiden University Medical Center in the Netherlands.



"Taking a so-called power nap may be useful for certain individuals, but naps should not be too long," she wrote in a commentary about the findings of the study, published last week in the journal Sleep Medicine.


The nap culture

The findings cannot prove a cause-and-effect relationship between napping and diabetes, the researchers cautioned. It is possible that diabetes itself induces tiredness, which may encourage napping.


In China, however, as in many other societies, napping is well accepted and routinely practiced by all age groups. The commonness of this habit makes it less plausible that regular napping is caused by high glucose levels[3] or diabetes, the researchers said.


In a 2010 study of Chinese nappers, participants who reported taking naps frequently — four to six days a week — were about 50 percent more likely to have diabetes than those who napped less frequently. The results held after controlling for other risk factors and excluding people who were potentially ill and who had daytime sleepiness.


In that study, the researchers concluded that "it is less likely that diabetes leads to daytime sleepiness. This raises the possibility that napping may increase the risk of diabetes."


How could long naps lead to diabetes?

Diabetes[4] is group of metabolic diseases in which the person has high blood sugar because the body doesn't produce enough insulin to remove excess glucose from the blood, or because the cells have become resistant to insulin.


Previous studies have suggested a link between diabetes and either too much or not enough nighttime sleep[5] . It is possible that sleeping during the day, too, disturbs the internal clock that regulates the 24-hour cycle of processes in the body, including the release of insulin, whereas naps that are short enough do not have such an effect, the researchers said.


It is also possible that people who take longer naps tend to sleep less at night, and it could be the loss of nighttime sleep that affects diabetes risk, Lucassen said.


Email Bahar Gholipour[6] or follow her @alterwired . Follow LiveScience @livescience , Facebook & Google+ . Original article on LiveScience .[7] [8] [9] [10] [11]



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  • To Nap Or Not To Nap?


    If you've got a big project you have to really focus on, or especially if you have to drive, hit the hay. If the rest of the workday looks like smooth sailing, or you often have trouble sleeping at night, skip the nap.

    "Naps are sort of a double-edged sword," warns Dr. Epstein. "If you're indeed sleepy and it's going to interfere with your performance, the best way to get over that is to go to sleep. But if you have trouble sleeping at night, taking a nap can be a problem, because if you sleep in the daytime you won't sleep at night."

    You've also got to be tired enough to fall asleep during the day. "Well-rested people don't have the ability to power nap and that's great," says Maas. "It's much better to get good nocturnal sleep and not be able to than to <em>have</em> to power nap. While we do have a natural dip in our circadian rhythms that usually occurs in the afternoon, that is exacerbated by not having good nocturnal sleep."




  • What's The Best Time For A Nap?


    Because of the natural cycles of our circadian rhythms, we are at our most tired twice during a 24-hour period. One peak of sleepiness is usually in the middle of the night, so the other, 12 hours later, falls smack-dab in the middle of the afternoon. "It's not that [there's] a good time to get the nap, it's that's the time you're going to be sleepy," explains Dr. Epstein. "It's a physiologic basis for a siesta," he says, and also why so many of us feel a slump around that time and head for the coffeemaker.

    If you get enough sleep at night, chances are you won't be bothered by the mid-afternoon peak of sleepiness. But if you're sleep-deprived, you'll feel that "sleep debt" greater in the afternoon, and be more inclined to nap.




  • Where Should You Nap?


    "The more comfortable you can get, the easier it is to fall asleep," says Dr. Epstein. That could mean closing your office door and dimming the lights, or finding an unused conference room, parking yourself on a common area couch, or even just putting your head down on your desk, he says.

    But sleep-chasers should also get creative. Many large companies, especially in their headquarters, have infirmaries or other first-aid offices. Maas suggests calling to see if they have any available beds. Or, in warm climates, lie down for a few minutes on a bench outdoors. Desperate? "Even restrooms give you an opportunity to sit for 10 minutes," he only half-jokes.

    Better still, try heading out for a nap on your next "lunch" break -- no one has to know you're not actually eating! "A lot of workers are kind of sneaky in these naps, they'll go out to the parking lot and take a quick snooze," says Maas, but most are allowed (if not legally required) to take a break during the day. Or, head to a local spa that provides nap rooms for a fee. Locations are popping up <a href="http://money.cnn.com/2008/08/21/smallbusiness/naps_for_sale.fsb/index.htm" target="_hplink">in numerous cities</a>, reports CNN Money.




  • What Else Do You Need?


    The same sleep hygiene rules apply to naps as to nighttime rest, namely that you want the environment to be quiet, dark and cool, says Maas. That might mean bringing an eye mask or ear plugs to work, he says, especially if you're opting for a nap on a communal couch.




  • How Long Should You Nap?


    Maas's definition of the power nap calls for only 10 to 15 minutes of rest, but Dr. Epstein says even up to 30 can still be beneficial. However, sleep much longer than that and you'll enter deep sleep, leaving you feeling groggy when you wake up, warns Maas.

    If you really need more than 15 minutes of shuteye, you're better off shooting for a full 90 to guarantee waking up feeling refreshed, as that's how long it takes your body to complete an entire REM cycle, he explains. So set a cell-phone alarm and then get back to business.




  • Should You Skip Caffeine?


    "Caffeine acts as a way to avoid sleepiness, but it's not a replacement for sleep," says Dr. Epstein. If you have a big project to focus on in the afternoon, caffeine can help you power through the work, but it won't do anything to chip away at your sleep debt, he explains. Plus, if you resort to caffeine too late in the day you risk messing with your nighttime sleep.

    As long as you're four to seven hours away from bedtime, there's no real need to skip your afternoon pick-me-up, even if you're going to steal away for some zzz's. In fact, <a href="http://www.sciencedaily.com/releases/2010/05/100511192248.htm" target="_hplink">caffeine can even improve your performance</a> later in the day. It takes some time for the caffeine to kick in, so some experts suggest what's been dubbed a "caffeine nap" -- drinking a cup of coffee before a 20-minute nap, then waking up to "maximum alertness," says Dr. Epstein.




  • Boss Won't Go For It?


    Smart, educated companies are catching on to the fact that sleepy employees are bad for their bottom line and promoting short breaks as a potential solution.

    If your boss is at the other end of the spectrum, presenting the facts might be a good idea. Many corporations are already promoting preventive health and wellness programs focused on exercise and nutrition, says Maas, so why not add sleep? "They've got to realize that there are three things that determine longevity: nutrition, exercise we're already doing a lot about, but we're totally ignoring the third component, which is sleep," says Maas. "Sleep is treated as a luxury in American society, and it's a necessity."




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