Specifically, the study found that people who get six hours or less of sleep a night are four times more likely to catch a cold when exposed to the virus than people who snooze for seven hours or more.
The findings support the growing evidence that insufficient sleep can contribute to the onset or development of illness.
As the study’s authors explain in their paper, sleep helps regulate the immune system, and therefore may play an important role in helping the body resist infections like the common cold.
Many Americans do not get enough sleep. In a 2013 Gallup survey, a third of the people questioned said they had not received the recommended minimum of seven hours of sleep within the previous 24 hours.
For the study, researchers at Carnegie Mellon University, the University of Pittsburgh Medical Center and the University of California, San Francisco (UCSF), recruited 164 healthy men and women, aged 18 to 55 years, over a five-year period (2007 to 2011). The participants underwent two months of interviews and filled out several questionnaires to collect demographic information (such as education and income levels), as well as information about their health habits and psychological temperament.
The participants’ sleep patterns were then tracked for a week with a watch-like motion-sensing device (similar to a Fitbit). The participant also kept sleep diaries.
At the end of the week, the participants were sequestered in a hotel, where the researchers sprayed a live common cold virus (rhinovirus 39) into their noses. The participants were then monitored (still sequestered) for a week. Mucus samples were taken and analyzed daily to see if the virus had taken hold and launched an infection.
The researchers found that 39 percent of the people who had slept for less than six hours a night in the week leading up to being exposed to the virus got sick. That compared with only 18 percent of the people who had slept for more than seven hours.
That meant that people who had slept less than six hours were 4.2 times more likely to catch the cold than those who slept for more than seven hours. The likelihood of getting ill was slightly higher — 4.5 times — for those who slept for less than five hours a night.
Sleeping less than seven but more than six hours did not appear to increase risk. Also, fragmented sleep was not found to be a predictor of cold susceptibility.
The findings held even after adjusting for factors that might affect illness, including whether or not the participants smoked, their perceived stress levels, their body mass index (BMI), the season of the year, and preexisting levels of antibodies to the virus (measured through blood samples).
“Sleep goes beyond all the other factors that were measured,” said Aric Prather, the study’s lead author and an assistant professor of psychiatry at UCSF, in a statement released with the study. “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.”
Caveats and implications
The major strength of this study is that it measured sleep length objectively (rather than relying on people’s self-reports of their sleeping patterns). Also, the results are based on the participants’ normal sleep behavior, not on an artificial sleep-deprivation cycle imposed on them in a sleep laboratory.
But the study also has weaknesses. It included relatively few people, which resulted in very wide confidence intervals for the estimates of risk of getting a cold at certain sleep lengths. For example, the confidence intervals were 1.08 to 18.69 for the group that slept less than five hours. The wider the confidence interval in a study, the less certain we can be about the results.
Also, it’s important to note that the study’s results do not mean that insufficient sleep causes the common cold. It only suggests an association between poor sleep and an increased susceptibility to becoming infected once exposed to the virus.
Getting a good night’s sleep should be a priority for all of us — for a host of health-related reasons. But your best bet for protecting yourself from viruses like the common cold this coming cold and flu season is even simpler: Wash your hands frequently with soap and water, and avoid touching your eyes and nose with unwashed hands.
Although this new study was funded in part by public money from the National Institutes of Health, it is behind a paywall on the Sleep website.