To ward off a cold, ditch the vitamin C and get some shut-eye instead.
Thanks to the efforts of 164 intrepid adults who allowed investigators to drop particles of rhinovirus into their noses and conduct detailed examinations of their nasal cavities, researchers have determined that sleeping for only six hours a night — or less — will make you much more vulnerable to the common cold.
Compared to study participants who slept for more than seven hours a night, those who slept for five to six hours were 4.24 times more likely to develop a laboratory-confirmed cold. Even worse, those who snoozed for less than five hours a night were 4.5 times more likely to get sick after being deliberately exposed to the virus.
The people who slept for 6.1 to seven hours a night also were more susceptible than their longer-sleeping counterparts, but their risk of a cold was only 66% higher, according to a study published this week in the journal Sleep.
Researchers from UC San Francisco, Carnegie Mellon University and the University of Pittsburgh considered a variety of other factors that might influence one's vulnerability to a cold. For instance, they asked study participants about their smoking and drinking habits, whether they were stressed out, how much money they made and how much exercise they got. They included standard demographic information like age, gender and body mass index. And they ran tests to see if the study participants had preexisting antibodies to rhinovirus 39, the strain used to infect them during the experiment.
Even when they took all these things into account, they still found that sleep duration was the most important factor in predicting a person's risk of becoming sick.
"It goes beyond feeling groggy or irritable," study leader Aric Prather of UCSF said in a statement. "Not getting sleep fundamentally affects your physical health."
Some of Prather's co-authors had previously found that people who got "short sleep" were more vulnerable to colds. However, that study relied on self-reported sleep data from study participants who might have overestimated their hours of shut-eye.
So this time, they outfitted people with Actiwatches, which provided an objective measure of their sleep for seven consecutive nights before being exposed to the cold virus.
For the study participants, that was the easy part. To be included in the study, they had to give three blood samples and submit to other medical tests to be sure they were virus-free. They were interviewed every day for two weeks so that the research team could assess their "positive emotions."
They agreed to spend six days quarantined in a hotel and submitted to a nasal examination and daily nasal lavages. They collected their used tissues so that researchers could weigh them and figure out how much mucus they had produced. Most importantly, they let researchers administer nasal drops teaming with rhinovirus. (Each participant was paid $1,000 for his or her trouble.)
Among the 164 people, 76% became infected with rhinovirus, and 29% came down with "a biologically verified cold," the researchers found. But the risk wasn't spread evenly among all 164 participants. Instead, the statistical analysis showed that the less they slept, the more likely they were to get sick.
The results are in line with other studies showing that sleep deprivation takes a toll on the immune system, in part by handicapping T cells. Although the study doesn't prove that short sleep directly caused people to catch a cold, its design ruled out the possibility that the opposite was true (i.e., that a cold caused people to have trouble sleeping).
An editorial that accompanied the study described the results as "the first solid scientific evidence that sleep makes us more resistant to the common cold."
Prather, whose research focuses on how sleep relates to physical and mental health, said he hoped the findings would discourage people from burning the midnight oil.
"We need more studies like this to begin to drive home that sleep is a critical piece to our well-being," he said.