The less a person slept, the more likely he or she was to develop a cold (there was a graded association between infection rate and average sleep duration). Participants who slept fewer than 7 hours were 2.94 times more likely to develop a cold than those who had 8 hours or more sleep. “When the components of clinical illness (infection and signs or symptoms) were examined separately, sleep efficiency but not sleep duration was associated with signs and symptoms of illness,” they wrote, but “neither was associated with infection.”