Want to avoid a cold? Sleep on it

Getting a good night's sleep might not cure the common cold, but new research hints it could prevent one.

People who averaged less than seven hours of sleep a night were about three times more likely to develop cold symptoms than others who got eight or more hours of sleep, Pittsburgh researchers report in the Archives of Internal Medicine. Others who had a hard time falling asleep or woke up in the middle of the night fared even worse: Their chances of coming down with a cold were up to 5 and a half times higher than people who were sound asleep -- and stayed that way -- as soon as their heads hit the pillow.

"This is a huge effect," Dr. Charles Czeisler, chief of sleep medicine at Brigham and Women's Hospital, said in an interview. He was not involved in the study. "These results really fit in very well with what has been becoming increasingly clear, which is that sleep has major effects not only on the brain in terms of alertness and performance, but also on the health of the body."

Sheldon Cohen, a professor in the department of psychology at Carnegie Mellon University, led the clinical trial in which 153 healthy men and women told researchers every day for two weeks how long and well they slept and how rested they felt. The volunteers were then quarantined in a hotel, where cold-causing rhinoviruses were dropped into their noses. For five days they were monitored for sneezing, coughing, stuffy noses, and other cold symptoms. Their noses were tested for the presence of the virus, the tissues they blew their noses into were weighed for mucus, and dye was dropped into their noses to test how quickly they cleared congestion.

Among the 153 study subjects, 135 people were infected and 54 developed a cold. After taking into account a wide variety of factors, including age, weight, socioeconomic status, perceived stress, smoking, and alcohol consumption, how long and how well they slept were the strongest predictors of who would come down with a cold. Feeling rested was not associated with whether they developed a cold.

Of the two factors, sleep efficiency was a stronger predictor than sleep duration. Even if eight hours of sleep was disturbed only 2 percent to 8 percent of the time, or 11 to 38 minutes of being awake, there was a four times greater likelihood of developing cold symptoms than among people who were asleep 99 percent or 100 percent of their time in bed, Cohen said in an interview.

These findings are consistent with what other studies have found. In earlier research cited in the Archives article, researchers deprived people of sleep and then tested their response to a flu shot compared to people who got their normal amount of sleep. The sleep-deprived subjects developed half the number of antibodies from their flu vaccinations that the other subjects did, suggesting sleep helps the immune system mount a more robust defense against disease.

A biological mechanism that would explain the link between sleep and cold symptoms is not known, Cohen said, but previous research suggests it might involve the release of inflammatory chemicals, which cause some of the symptoms of colds. Inflammation is implicated in not just infectious diseases but also in illnesses from autoimmune disorders to heart disease.

"It does have potential implications for a lot of inflammatory diseases," Cohen said about the sleep and colds study. "We don't regulate our immune systems as well when we don't get enough hours of sleep."