WASHINGTON (Reuters) - People who sleep less than seven hours a night are three times as likely to catch a cold as their more well-rested friends and neighbours, U.S. researchers reported on Monday.

The study supports the theory that sleep is important to immune function, said Sheldon Cohen and colleagues at Carnegie Mellon University in Pittsburgh.

Volunteers who spent less time in bed, or who spent their time in bed tossing and turning instead of snoozing, were much more likely to catch a cold when viruses were dripped into their noses, they found.

People who slept longer and more soundly resisted infection better, they reported in the Archives of Internal Medicine.

“Although sleep’s relationship with the immune system is well-documented, this is the first evidence that even relatively minor sleep disturbances can influence the body’s reaction to cold viruses,” Cohen said in a statement.

“It provides yet another reason why people should make time in their schedules to get a complete night of rest.”

Cohen’s team tested 153 healthy volunteers, locking them in a hotel for five days after infecting them with a cold virus.

They had been interviewed daily for the previous two weeks to get details on their sleep patterns. They were tested for cold symptoms after the five-day lockup and had blood tests for antibodies to the virus.

The men and women who reported fewer than seven hours of sleep on average were 2.94 times more likely to develop sneezing, sore throat and other cold symptoms than those who reported getting eight or more hours of sleep each night.

Volunteers who spent less than 92 percent of their time in bed asleep were 5 1/2 times more likely to become ill than better sleepers, they found.

Sleep disturbance may affect immune system signalling chemicals called cytokines or histamines, the researchers said.

“Experiments that explore the relationship between sleep and immune function often involve sleep deprivation or study subjects with sleep disorders, which are often rooted in psychiatric conditions that influence other aspects of health,” Cohen added. “This research points to the role played by ordinary, real-life sleep habits in healthy persons.”