mardi 1 septembre 2015

Why You Should Get Plenty Of Sleep Tonight

Why You Should Get Plenty Of Sleep Tonight

Lack of sleep can lead to bad outcomes: from crankiness to extreme mental distress.

Now researchers report an association between insufficient sleep and getting sick. Specifically, they conclude that shorter sleep duration was associated with increased susceptibility to the common cold. Adults who slept fewer than 5 hours or between 5 and 6 hours were at greater risk of developing a cold compared to those sleeping more than 7 hours per night, according to the study, published in the journal Sleep.

Seniju/Flickr

Seniju/Flickr

The authors conclude:

Given that infectious illness (i.e., influenza and pneumonia) remains one of the top 10 leading causes of death in the United States, the current data suggest that a greater focus on sleep duration, as well as sleep health more broadly, is indicated.

NPR reports further on the study:

Aric Prather, a psychologist at the University of California, San Francisco, who studies how our behaviors can influence our health…wanted to document the extent to which a good night’s sleep is protective. So, he and a group of colleagues recruited 164 healthy men and women — their average age was 30 years old — to take part in a study. Using sleep diaries and a device similar to a Fitbit, the researchers assessed each participant’s sleep for a week.

Then the scientists sprayed a live common cold virus into each person’s nose.

“We infected them with the cold virus,” Prather says, then quarantined everybody and watched to see who got sick…

“What we found was that individuals who were sleeping the least were substantially more likely to develop a cold,” Prather says.

In fact, the adults who averaged five or six hours nightly during the study were four times more likely to catch the cold than people who slept at least seven hours per night.

Analyzed another way: About 39 percent of those who slept six hours or less got sick. Of those who slept more than six hours, “only 18 percent got colds,” Prather says. “It’s striking.”

Why a good night’s sleep is protective isn’t yet clear, but the scientists have a hunch.

“There’s evidence that people who don’t get enough sleep show higher levels of inflammation,” says Sheldon Cohen, a psychologist at Carnegie Mellon University who’s been studying the common cold for decades and co-authored the study.

Other factors and behaviors may increase susceptibility too, research suggests. For instance, age may play a role, and smoking, chronic stress and a lack of exercise can all make us more susceptible.

The National Sleep Foundation recommends that adults get between 7 and 9 hours of sleep; children and teenagers should be getting even more.

Marvin Wang, M.D., a pediatrician who advocates for later school start times so that teenagers can get enough sleep, says the new study is “convincing.” I asked Wang, who is director of of newborn nurseries at Massachusetts General Hospital and an assistant professor of pediatrics at Harvard Medical School, to comment further and here’s his emailed response:

This study has done well to control for as many factors as they could to determine whether sleep duration affects one’s fallibility to the common cold virus. The interesting conclusion is that, based on their study, it was sleep duration alone that affected the test subjects’ likelihood of getting sick. As well, sleep fragmentation (i.e., waking up frequently during the night) did not have a significant effect on being ill.

The casual reader might say that this has nothing to do with teens (or younger children), as the test subjects were all adults. One could easily say that the immature immune system of the younger person is more susceptible to the common colds, and as one experiences contact with viruses over a lifetime, the frequency of catching a cold diminishes.

However, you could very loosely abstract these results to a younger population by realizing that the authors tested the antibody levels to the virus prior to the viral exposure. Thus, if the test subject had undetectable levels of antibody prior to the study, he/she is as vulnerable to the virus as a teenager (who, presumably, has also not seen the virus before, becoming equally as susceptible).

The danger of making that association, though, is that you depend on the sensitivity of the antibody test. Just because a test says “undetectable,” does that mean that the antibody doesn’t exist in the body? Does the detectable threshold of the test define the body’s true ability to mount an appropriate immune response? It’s hard to say, and no one would guarantee that statement.

On the whole, though, the study does make a convincing argument that at an extreme low duration of sleep (less than 5 hours of sleep), controlling for other factors (e.g. lifestyle issues), there is a higher likelihood of catching a cold, which we all anecdotally believed to be true already.

And here are more details on the study from the news release:

For the study, 164 adults underwent two months of health screenings, interviews and questionnaires to establish baselines for factors like stress, temperament, and alcohol and cigarette use. The researchers also tracked their sleep patterns for seven days using a watch-like sensor that measured the duration and quality of sleep throughout the night. Then, the participants were sequestered in a hotel, administered the cold virus via nasal drops and monitored for a week, collecting daily mucus samples to see if the virus had taken hold.

They found that subjects who slept less than six hours a night were 4.2 times more likely to catch the cold compared to those who got more than seven hours of sleep, and those who slept less than five hours were 4.5 times more likely.

“Sleep goes beyond all the other factors that were measured,” Prather said. “It didn’t matter how old people were, their stress levels, their race, education or income. It didn’t matter if they were a smoker. With all those things taken into account, statistically sleep still carried the day and was an overwhelmingly strong predictor for susceptibility to the cold virus.”

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