New research from Carnegie Mellon University finds that those who get less than seven hours sleep a night are three times as likely to catch a cold. Furthermore, those who sleep poorly were at a five times higher risk of catching a cold.

The researchers paid healthy adults $800 to have cold viruses sprayed up their noses. Participants then spent five days in a hotel to see if the virus sickened them. The study’s showed that those who habitually slept eight hours or more were significantly less likely to become sick than those who slept less than seven hours or slept restlessly.

"The longer you sleep, the better off you are, the less susceptible you are to colds," said Sheldon Cohen, the study’s lead author.

Although previous studies have connected adequate sleep with a boost in the immune system at the cellular level, the current study is the first to demonstrate that minor sleep disturbances can raise the risk of becoming sick, said Dr. Michael Irwin, who studies immune response at the University of California, Los Angeles.

"The message is to maintain regular sleep habits because those are really critical for health," Irwin, who was not involved in the study, told the Associate Press.

During cold season, it is not always possible to keep away from sneezing family members and co-workers. The study sought to simulate those conditions by exposing participants to a rhinovirus, with most becoming infected.

However, not everyone developed a cold. The researchers found that those who slept less than seven hours a night in the weeks prior to exposure to the rhinovirus were three times more likely to catch a cold than those who slept eight hours or more.

To find willing participants for the study, the researchers placed ads and recruited 78 men and 75 women for the study. All were healthy, ranging in age from 21 to 55, and willing to submit to exposure to the virus.

The researchers recorded the participants’ sleeping habits for two weeks, and interviewed them by telephone about their sleep the previous night. Participants were asked what time they went to bed, when they awakened, how much time they spent awake during the night and whether or not they felt rested in the morning.

Next, the participants checkED into a hotel, where they were given nose drops that contained the rhinovirus. Five days later, they were asked to report any signs and symptoms of a cold. Researchers measured their runny noses by weighing their used tissues, and tested for congestion by squirting dye in the participants' noses and measuring how long it took to get to the back of their throats. The researchers also collected mucus samples to test for the virus, and obtained participants' blood samples to test for antibodies to the virus.

After five days, the study found that the virus had infected 135 of the 153 volunteers. However, only 54 people became sick.

The researchers found that restless sleeping was linked with a greater risk of catching a cold. Indeed, those who slept restlessly 8 percent of their time in bed were five times more likely to get sick than those who were sleepless only 2 percent of the time.

Interestingly, the researchers found that feeling rested was not linked to staying well. Cohen said he could not identify the cause for this, other than feeling rested is more subjective than remembering when a person went to bed and woke up.

The researchers accounted for other factors, such as smoking, stress, drinking, and lack of exercise, which may make people more vulnerable to catching a cold. However, the connection between sleep and cold resistance was still present.

Cold symptoms such as congestion and sore throat are caused by the body's fight against a virus, not the virus itself, said Cohen. People who produce the precise amount of infection-fighting proteins, called cytokines, to fight the virus will not even be aware their bodies are doing so. However, if they produce too much they will feel sick.