Catching cold less common for those who get good sleep
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With a shake of a finger, mother told you how important sleep was to good health, and now science is supporting her contention.
People who sleep fewer than seven hours a night experience the common cold almost three times more often than those who sleep eight or more hours.
But the quality of sleep is even more important than length of sleep in determining whether a person infected with a cold virus develops symptoms that include sneezing, runny nose, nasal congestion and sore throat.
That's the conclusion of research led by Sheldon Cohen, the Robert E. Doherty Professor of Psychology at Carnegie Mellon University.
His team's study was published yesterday in Archives of Internal Medicine and represents the first evidence that even relatively minor sleep disturbances can influence the body's reaction to cold viruses.
"It provides yet another reason why people should make time in their schedules to get a complete night of rest," Dr. Cohen said.
It's already been proven, he said, that chronic stress -- unemployment or problems with work or marriage -- place a person at greater risk for common cold symptoms.
His team's research has shown that healthy people who receive eight hours of undisturbed sleep become infected with the cold virus, but their immune system works to control the virus without producing cold symptoms.
People receiving fewer than seven hours of sleep are 2.94 times more likely to experience cold symptoms than those receiving eight or more hours of sleep.
But that's not the most dramatic gesundheit in the study.
"The big finding here is not duration of sleep but our sleep-efficiency finding," Dr. Cohen said. "Sleep efficiency is more strongly linked with colds."
Sleep efficiency is the amount of time asleep divided by the time in bed. If a person goes to bed at midnight, falls asleep immediately then awakens at 8 a.m. without any disruptions, that person has 100 percent sleep efficiency.
The person who goes to bed at midnight but remains awake for an hour only to awaken for another hour at 4 a.m. then finally arises at 8 a.m. has received only six of eight potential hours of sleep, for a 75 percent efficiency rating.
The study shows that loss of only 2 to 8 percent in sleep efficiency puts a person at four times the risk of getting a cold when exposed to a virus, while those with an efficiency less than 92 percent face 5.5 times the risk.
"A small loss of efficiency led to substantial increase in risk," Dr. Cohen said.
In the study, the sleep patterns of 153 healthy volunteers, including 78 men and 75 women, were documented each day for two weeks regarding the length and quality of sleep the previous night. Then they each had a cold virus sprayed into their noses. Participants were sequestered in a hotel for five days and monitored for such symptoms as sneezing, nasal congestion and sore throats.
Each participant was paid $800 to be in the study.
While 135 of the 153 were infected with the cold virus, just 54 developed cold symptoms.
Feeling rested was not a factor in development of cold symptoms. Dr. Cohen also said factors like smoking, stress and depression, were controlled in the study.
The hypothesis reduces to this: Sleep might regulate the immune system to produce the right amount of response without going overboard. So people whose bodies make the perfect amount of infection-fighting proteins called cytokines will show no symptoms and be unaware that their bodies are even fighting a virus. When their systems produce too many cytokines, however, the excessive inflammatory response produces cold symptoms.
Cold symptoms result from the immune response, not the virus itself.
Dr. Cohen said the study's strength was providing accurate measurement of sleep efficiency. "This research points to the role played by ordinary, real-life sleep habits in healthy persons," he said.
Prior research has tied lack of sleep to greater risk of weight gain, heart disease, high blood pressure, stroke and diabetes. Although no sleep expert, Dr. Cohen said people should not have a television in their bedrooms. They also should follow routine sleep schedules and avoid drinking caffeinated beverages before bed.
By all accounts, the study is nothing to sneeze at.
Dr. Michael Irwin, who researches immune response at the University of California, Los Angeles, but was not involved in the study, said it provides healthful advice.
"The message is to maintain regular sleep habits because those are really critical for health," he said.
Correction/Clarification: (Published Jan. 15, 2008) Sleep efficiency is the amount of time asleep divided by the time in bed. An incorrect definition was included in this story as originally published Jan. 14, 2009 about research at Carnegie Mellon University linking sleep to a body's reaction to cold viruses.
First Published January 13, 2009 12:00 am