The study, published in the Archives of Internal Medicine, found people who get less than seven hours of sleep per night appear about three times as likely to develop respiratory illness following exposure to a cold virus as those who sleep eight hours or more.

Sheldon Cohen of Carnegie Mellon University in Pittsburgh and colleagues studied 153 healthy men and women -- average age 37 -- between 2000 and 2004. Participants were interviewed daily over a two-week period, reporting how many hours they slept per night, what percentage of their time in bed was spent asleep and whether they felt rested.

They were then quarantined and administered nasal drops containing the common-cold-causing rhinovirus. For five days, the study participants reported any signs and symptoms of illness and had mucus samples collected from their nasal passages for virus cultures.

About 28 days later, they submitted a blood sample that was tested for antibody responses to the virus.

Lower sleep efficiency -- percentage of time in bed spent sleeping -- was also associated with developing a cold. Participants who spent less than 92 percent of their time in bed asleep were five-and-a-half times more likely to become ill than those whose efficiency was 98 percent or more.

Feeling rested was not associated with colds, the study found.