Inadequate sleep can raise the risk of catching a cold, says a new study. Researchers at Carnegie Mellon University have found that people who sleep less than seven hours a night and do not sleep soundly are vulnerable to getting a cold by threefold as compared to those who shut-eye for eight hours or more.

According to them, sleep is linked to the strength of the immune system very closely and this is why people feel tired when they are ill or have an infection. In fact, the researchers have based their findings on an analysis of 153 healthy people with an average age of 37.

From interviews over 14 days, they calculated the average amount of time the subjects slept for each night along with their "sleep efficiency" -- defined as the amount of time asleep divided by the time spent in bed.

The researchers then asked the participants if they felt rested or not. They were subsequently quarantined and given nasal drops that contained the rhinovirus, the most common virus that causes colds, before being monitored for symptoms and then tested for actual infection.

More than a third of the volunteers developed a cold, according to tests of samples, while 43 developed a cold as per self-reported symptoms, leading British newspaper The Daily Telegraph reported.

Lower sleep efficiency was also associated with developing a cold -- participants who spent less than 92 per cent of their time in bed asleep were five-and-a-half times more likely to become ill than those whose efficiency was 98 per cent or more, the study found.

"In sum, according to our study results, measures of sleep predicted susceptibility to the development of a cold," lead researcher Dr Sheldon Cohen wrote in the 'Archives of Internal Medicine' journal.