Is there a link between getting a good night’s sleep and the ability to ward off winter ailments like bronchitis, colds and pneumonia?

There’s plenty of evidence linking poor sleep to chronic diseases like diabetes and heart disease, but remarkably few good clinical trials have looked at whether sleep is a bulwark against respiratory infections. One such study, published last September in the journal Sleep, reported that adults who slept less than five or six hours a night were four times more likely to catch a cold than those who slept at least seven hours.

The trial was one of the first to objectively measure the amount of sleep volunteers got before they were deliberately exposed to the common cold through nasal drops containing the cold virus. A clinical trial in 2009 that relied on participants’ own accounts of their sleep habits also found sleep protective against the common cold. In that trial, volunteers who reported sleeping fewer than seven hours a night were nearly three times more likely to catch a cold after exposure than those who slept eight hours or more.

An observational study from 2012 of nearly 60,000 women in the Nurses Health Study II also suggested sleep patterns may affect pneumonia risk. It found that women who slept five hours or less were more likely to develop pneumonia, though oddly enough, those who slept nine hours or more were also at higher risk. Dr. Sanjay Patel, the study’s author, suggested that the women who slept excessively may have suffered from poor quality sleep. It is also possible that being in the sleep position for an extended time increases susceptibility to pneumonia, since bacteria that colonize the nose and throat may drip into the lungs, he said. Sleep scientists were not aware of any studies examining the role of sleep in bronchitis.

Scientists are uncertain how sleep might help fight infections, but sleep is known to play a role in the regulation of the immune system. Studies suggest that sleep deprivation, for example, may lead to a weaker antibody response to vaccination, Dr. Patel said. Insufficient sleep “seems to reduce the functioning of cells like natural killer cells and lymphocytes that are important in giving you an immune response.”