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Regular, moderate exercise reduces the risk of colds in postmenopausal women

October 26, 2006

SEATTLE - Postmenopausal women who want to decrease their risk of colds would be well advised to dust off their sneakers and get moving, suggests a new study led by researchers at Fred Hutchinson Cancer Research Center.

Through the first randomized clinical trial to investigate the impact of moderate physical activity on common-cold incidence, Cornelia (Neli) Ulrich, Ph.D., and colleagues found that postmenopausal women who exercised regularly for a year had about half the risk of colds compared to those who did not work out routinely. The findings appear in the November issue of The American Journal of Medicine.

"This adds another good reason to put exercise on your to-do list, especially now that cold season is here," said Ulrich, the paper's senior author and an associate member of the Hutchinson Center's Public Health Sciences Division. However, Ulrich is quick to point out that regular exercise in moderation - such as 30 to 45 minutes of brisk walking each day - is the key; other studies have shown that excessive, exhaustive exercise can deplete immune function and increase the risk of colds.

The researchers found that the ability of moderate exercise to ward off colds seemed to increase over time. "The enhanced immunity was strongest in the final quarter of the year-long exercise intervention," Ulrich said. "This suggests that when it comes to preventing colds, it's really important to stick with exercise long term." Overall, the non-exercisers experienced about twice as many colds as the exercisers, but in the last three months of the intervention, the non-exercisers had a threefold greater chance of coming down with colds.

The yearlong study involved 115 previously sedentary, overweight, postmenopausal Seattle-area women. None smoked or took hormone-replacement therapy. Half were randomly assigned to a moderate-intensity, aerobic-exercise group and half, who served as a comparison group, attended a weekly stretching class.

While the members of the exercise group were asked to work out at home and at a gym for 45 minutes a day, five days a week, in fact they achieved an average of about 30 minutes of exercise per day. "They were supposed to do a little more exercise, but even so, we found it was enough activity to boost immune function in the long run," Ulrich said.

Brisk walking was the activity of choice, accounting for 52 percent of gym-based and 74 percent of home-based exercise. "It's been shown that just a 30-minute walk can increase levels of leukocytes, which are part of the family of immune cells that fight infection," Ulrich said, referring to a possible biological explanation for the protective effect.

A major strength of this study was its yearlong duration, large number of participants and randomized, controlled, clinical-trial design, considered the gold standard of study designs in medicine.

Even though the study was larger and longer than others that have addressed the impact of exercise on the risk of colds and upper-respiratory infections, it still may not have had enough participants or followed them long enough to provide a definitive answer, cautioned first author Jessica Chubak, a research associate at the Hutchinson Center. "It would be interesting to see what would happen over the course of a longer exercise intervention," she said.

The overall goal of the study, funded by the National Cancer Institute, was to assess the impact of physical activity on markers of breast-cancer risk. In addition to reducing their incidence of colds, the women in the exercise group also achieved significant reductions in weight, total-body fat and intra-abdominal fat.

In addition to Ulrich, Chubak and colleagues at the Hutchinson Center, collaborators on the study also included investigators from the University of Washington, University of Alberta and University of New Mexico.

According to the National Institute of Allergy and Infectious Diseases, Americans suffer an estimated 1 billion colds per year, resulting in a leading cause of doctor visits and missed days from work and school. Adults in the United States report an average of two to four colds per year.

Fred Hutchinson Cancer Research Center