Deprived sleepers four times more likely to catch a cold: new study
People who sleep six hours a night or less are more than four times more likely to catch a cold, compared to those who get more than seven hours of slumber, finds a study published in the journal Sleep.
It’s no secret the lack of sleep can make you sick, but a new study presents the cold hard statistics: people who sleep six hours a night or less are more than four times more likely to catch a cold, compared to those who get more than seven hours of shut-eye a night.
In fact, sleep was the most important factor for catching a cold beyond all others measured in the study like stress, temperament, and alcohol and cigarette use.
“It didn't matter how old people were, their stress levels, their race, education or income. 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,” says Aric Prather, assistant professor of psychiatry at University of California, San Francisco, and lead author of the study published in the journal Sleep.
In Hong Kong, about two in three adults get more than seven hours of sleep a night, according to 2011 statistics from the Centre for Health Protection. This means around a third of Hongkongers are putting themselves at a higher risk for not only colds, but also chronic illnesses, disease susceptibility and even premature death.
Prather's previous studies have shown that people who sleep fewer hours are less protected against illness after receiving a vaccine. Other studies have confirmed that sleep is among the factors that regulate levels of T-cell, which play an important role in the immune system.
In his new study, Prather teamed up with Carnegie Mellon University psychologist Sheldon Cohen, who has spent years exploring psychological factors that contribute to illness.
The researchers recruited 164 volunteers from the Pittsburgh, Pennsylvania area between 2007 and 2011. The volunteers underwent two months of health screenings, interviews and questionnaires to establish baselines for factors like stress, temperament, and alcohol and cigarette use.
Participants also had their normal sleep habits measured for seven days through a watch-like sensor that measured the quality of sleep throughout the night.
At the end of that week, the participants were sequestered in a hotel and administered with the cold virus via nasal drops. They were monitored for a week, with daily collection of mucus samples to see if the virus had taken hold.
Participants who slept fewer than six hours a night were 4.2 times more likely to catch the cold compared to those who got more than seven hours of sleep, and those who slept fewer than five hours were 4.5 times more likely.
"It goes beyond feeling groggy or irritable," Prather says. "Not getting enough sleep affects your physical health."
Because the study is based on subjects’ normal sleep behavior, Prather says it shows the risks of chronic sleep loss better than typical experiments in which researchers artificially deprive subjects of sleep. "This could be a typical week for someone during cold season," he says.
In 2009, Cohen had done a similar study involving 153 healthy men and women – though participants’ sleep habits were based on self-reports rather than measured by sensors. It was found that people who slept fewer than seven hours a night were nearly three times more likely to get a cold than those who averaged eight or more hours of sleep.
Those who experienced insomnia or disrupted sleep fared even worse. Study subjects who scored lower than 92 per cent sleep efficiency — the percentage of time one actually sleeps between lying down to sleep and waking up the next morning — were five-and-a-half times more likely to develop colds than those with efficiency scores of 98 per cent or better.
Prather says sleep should be treated as a crucial pillar of public health, along with diet and exercise. But it's still a challenge to convince people to get more sleep.
"In our busy culture, there's still a fair amount of pride about not having to sleep and getting a lot of work done," he says. "We need more studies like this to begin to drive home that sleep is a critical piece to our well-being."