People who sleep less than seven hours a night appear to be almost three times as likely to catch a cold as those who sleep eight hours or more, a new study has found.
Quality of sleep may count even more than quantity. Those who spend as little as 25 minutes a night tossing and turning face more than five times the risk of sniffing and sneezing.
The age-old advice to get a good night's sleep is well-supported by medical research. Sleeping less than seven hours a night has been shown to increase the risk of high blood pressure, diabetes, weight gain and hardening of the arteries.
Studies have also found that serious sleep deprivation disrupts the immune system. But those were experimental studies that kept subjects up for most of the night, then measured their immune responses.
One of the surprising findings from the new study, published Monday in the journal Archives of Internal Medicine, was just how little it took to knock down defenses against the common cold.
"Very small disruptions in sleep, very small losses in terms of duration of sleep, were associated with pretty big increases in your probability of getting sick if you're exposed to a virus," said Sheldon Cohen, a professor of psychology at Carnegie Mellon University and the first author of the study. "It's not just insomniacs or people being deprived of sleep."
A team of researchers interviewed 153 healthy men and women each day for 14 days about the length and quality of their sleep the previous night. The 78 men and 75 women ranged in age from 21 to 55 years.
The volunteer participants were then sequestered in hotel rooms, exposed to a cold virus and observed for five days. Fifty-four of them came down with colds.
Controlling for numerous factors that can influence health -- including age, race, income, education, smoking, exercise and depression -- the study found that the longer and better participants slept, the better they were able to resist or fight off infection, Cohen said.
Sleep efficiency was defined as the percentage of time a person actually slept in the period between going to bed at night and getting up in the morning.
Participants with less than 92% efficiency were 5.5 times more likely to come down with a cold than those with 98% or more.
As for why this happens, Cohen believes that sleep disruption interferes with the immune system's ability to regulate itself.
The sniffling-and-sneezing symptoms of a cold are not the act of the virus itself but the result of your immune system's overly energetic response to the infection, Cohen said.
In the best-case scenario, your immune system would produce just enough pro-inflammatory cytokines to do the job.
"You want it to be able to turn itself off when it's supposed to," he said.