According to research appearing in the October, 2006 issue of the American Journal of Medicine (2006;119;937-942),  post-menopausal women who exercised regularly for at least one year had a lower incidence of colds than those who did not. The subjects were 115 postmenopausal women who were sedentary and either obese or overweight. They were divided into two groups. For 12 months one group did 45 minutes of moderate exercise, five days per week. The control group did 45 minutes of stretching.

The subjects filled out quarterly questionnaires about upper respiratory infections. The group that exercised had a lesser risk for catching a cold, which was more pronounced late in the study. In the final three months, the risk for colds in the control group was more than three time that for the group performing the exercise.

Other research, appearing in Medicine & Science in Sports & Exercise (2002; 34:1242-1248) evaluated 500 subjects over the course of a year to find how many colds they had and how often they exercised moderately (defined as activity more strenuous than a walk). The most active subjects had 25% fewer colds each year compared to the least active subjects.