THURSDAY, Oct. 26, 2006 (HealthDay News) -- Moderate daily exercise can help fend off the common cold, new research suggests.
Older women who walked for a half-hour daily for a year reported half the number of colds as women of similar age who didn't exercise, U.S. researchers report in the November issue of the American Journal of Medicine.
"There's been a lot of anecdotal evidence that exercise prevents infection, and colds in particular," said the study's lead author, Cornelia M. Ulrich, an associate member of the Fred Hutchinson Cancer Research Center in Seattle.
Her team's study is the first randomized clinical trial to look at the impact of moderate physical activity on the actual number of colds contracted, she said.
Ulich's team evaluated 115 overweight Seattle-area women who had previously shunned regular exercise. All were past menopause, and averaged 61 years of age.
Fifty-three of the women were assigned to the exercise group, where they spent 30 minutes daily, five days a week, doing moderate-intensity activity like brisk walking. Another 62 were assigned to a control group, which only attended a weekly 45-minute stretching class.
All the participants were asked not to change their dietary habits. And they answered questionaires every three months on cold symptoms or other upper respiratory infections.
"Overall, the non-exercisers got two times the number of colds," Ulrich said.
The benefit of exercise in reducing colds was even greater in the final three months of the study, she added.
"In the final three months, one of 10 exercisers had a cold, but one of three of the non-exercisers did," Ulrich noted. "Couch potato" types, "were more than three times as likely to get a cold," she said.
Ulrich also said that there was no overall difference in the risk of upper respiratory infections (like flu) between groups, but added that this could be due to the fact that more non-exercisers had received the flu vaccine.
While 42 percent of the stretchers had gotten the flu vaccine during the study, only 23 percent of the exerciser had.
Experts aren't sure just how exercise works to battle colds. "We think there are [positive] changes in the immune system," Ulrich said.
The study results make sense to David Nieman, a professor of health and exercise science at Appalachian State University, Boone, N.C., and a veteran researcher of the exercise/colds link. In his own research, Nieman found that walkers experienced half the number of days of cold symptoms as non-exercisers.
The new study, he said, adds more valuable information to the mix.
"I think it is another set of data that now adds to the growing awareness that one of the most powerful ways of keeping your sick days down is to do nearly daily [physical] activity," Nieman said.
In a report on exercise immunology, published in 2003 in Current Sports Medicine Reports, Nieman noted that positive immune changes take place during each bout of moderate physical activity. Over time, this translates to fewer sick days from colds or flu, he said.
But the new study does have some potential weaknesses, added Dr. Paul D. Thompson, director of cardiology at Hartford Hospital who co-authored an editorial that accompanied the journal report.
Infections were self-reported, he noted. "Colds were reduced [in the exercisers], but there was not a reduction in upper respiratory infections [overall]," he said. "Could subjects have 'reclassified?'" In other words, they may have described a cold as the flu, he said.
He also noted that the "control" stretching group worked in close proximity during the 45-minute sessions, which could have have left them more vulnerable to catching and spreading infection than the more-solitary walkers.
Even so, he said, the new study suggests there's yet another good reason to exercise.
Accoring to Thompson, regular physical activity "probably reduces the chance of colds, probably reduces the incidence of heart attacks and heart disease, helps prevent diabetes, helps control body weight and keeps you out of the nursing home."
To learn more about colds and flu, visit the U.S. Centers for Disease Control and Prevention.