People who sleep six hours a night or less are four times more likely to catch a cold when exposed to the virus, compared to those who get more than seven hours of sleep a night, scientists have found.

The findings, by researchers from University of California – San Francisco (UCSF), Carnegie Mellon University and University of Pittsburgh Medical Center, add to the growing evidence of the importance of sleep for our health.

This is the first study to use objective sleep measures to connect people’s natural sleep habits and their risk of getting sick, according to Aric Prather, assistant professor of Psychiatry at UCSF and lead author of the study.

“Short sleep was more important than any other factor in predicting subjects’ likelihood of catching cold,” Prather said.

“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,” Prather said.

Scientists have long known that sleep is important for our health, with poor sleep linked to 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 T-cell levels.

To learn how sleep affects the body’s response to a real infection, Prather collaborated with Carnegie Mellon psychologist Sheldon Cohen, the study’s senior author.

Cohen’s group gives volunteers the common cold virus to safely test how these various factors affect the body’s ability to fight off disease.

For this study, Prather approached Cohen about investigating sleep and cold susceptibility using data collected in his lab’s recent study, in which participants wore sensors to get objective, sleep measurements.

Researchers recruited 164 volunteers from the Pittsburgh area between 2007 and 2011. The recruits underwent two months of health screenings, interviews and questionnaires to establish baselines for factors such as stress, temperament, and alcohol and cigarette use.

The researchers also measured participants’ normal sleep habits a week prior to administering the cold virus, using a watch-like sensor that measured the quality of sleep throughout the night.

The researchers then sequestered volunteers in a hotel, administered the cold virus via nasal drops and monitored them for a week, collecting daily mucus samples to see if the virus had taken hold.

They found that subjects who had slept less than six hours a night the week before 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 less than five hours were 4.5 times more likely.

The study is published in the journal Sleep.