The viruses that cause the common cold are always lurking. But consider this: Even if we touch a doorknob or keyboard that's covered in cold germs from an infected person, we don't always catch the cold.
"Sometimes when we're exposed to viruses, we end up not getting sick," says Aric Prather, a psychologist at the University of California, San Francisco, who studies how our behaviors can influence our health.
Our immune systems often fend off the viruses that cause colds. But, how well our bodies mount this defense can vary.
Prather 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 โ their average age was 30 years old โ 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. The study's results appear this week in the journal Sleep.
"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," saysSheldon 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 alack of exercise can all make us more susceptible.
As for sleep's value, Prather's study is one more bit of evidence that many of us aren't getting enough. The National Sleep Foundationrecommends that adults get at least seven hours per night. And children and teens need even more.
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Transcript :
RENEE MONTAGNE, HOST:
Let's hear now about a better way of keeping colds away from you. NPR's Allison Aubrey reports on a new study that offers another way to at least cut the risk of catching a cold. Get more sleep.
ALLISON AUBREY, BYLINE: The viruses that cause the common cold are always out there, spreading from person to person. None of us see them coming. One minute we feel fine and the next...
(SOUNDBITE OF SNEEZING)
AUBREY: But here's something to think about. Even if we touch, say, a doorknob or a keyboard that's covered in cold germs from an infected person, we don't always catch the cold.
ARIC PRATHER: Sometimes when we're exposed to viruses in the natural environment, we end up not getting sick.
AUBREY: That's psychologist Aric Prather of UC San Francisco. He studies how our behaviors can influence our health. He says our immune systems often do fend off common cold viruses but how well our bodies do this can vary. Prather wanted to note the role a good night's sleep might play in making us less vulnerable.
PRATHER: It's been a long-held belief that, you know, if you don't get enough sleep, you're likely to get sick.
AUBREY: But how much sleep do you really need to protect yourself? Prather and his colleagues designed a straightforward experiment to find out.
PRATHER: So what we did is we recruited about 160 people and we measured their sleep, objectively, over a week.
AUBREY: Using a device similar to a Fitbit. All of the participants were healthy adults ranging in age from 18 to 55, and what happened next is that all of them were brought into a laboratory where researchers sprayed a live common cold virus into their noses.
PRATHER: What we did was we, in fact, infected them with the cold virus, and we kept them there for five days to see who, in fact, developed the cold.
AUBREY: It turned out that the people who were getting the least sleep were much more likely to end up with a cold compared to people who slept more.
PRATHER: Remarkably, what we found was that if you slept six or less hours on average, 39 percent of the people got colds, but if you slept more than six hours, only 18 percent got colds.
AUBREY: So in other words, getting more than six hours of sleep cut the risk in half.
PRATHER: It's striking.
AUBREY: It's not exactly clear how a good night's sleep protects us from colds, but Sheldon Cohen of Carnegie Mellon University who is the senior author on the paper and has been studying the common cold for years says inflammation seems to play a role.
SHELDON COHEN: So there's evidence that people who don't get sufficient sleep show higher levels of inflammation in general.
AUBREY: But Cohen says sleep is certainly not the only factor that influences the risk of the common cold. His research finds, for instance, that chronic stress and a lack of exercise can increase a person's susceptibility, too.
COHEN: Health behaviors tend to have pretty big effects.
AUBREY: So when it comes to sleep, this study adds to the evidence that lots of us need more of it. The National Sleep Foundation recommends at least seven hours for adults per night and even more for children and teens. Allison Aubrey, NPR News. Transcript provided by NPR, Copyright NPR.