Fitness Fights Colds

Summarized by Robert W. Griffith, MD
December 4, 2006

Summary

Moderate-intensity exercise training for a year reduces the frequency of common colds in overweight postmenopausal women.

Introduction

Most adults in the USA get two to four colds a year, mostly in the winter months. The older you are, the fewer colds you get. But there are a number of risk factors - lack of sleep, exposure to small children, poor air quality, dampness in the house, and smoking which have all been blamed, along with genetic factors. No wonder that promoters of cold-preventive nostrums can usually find a good selling point.

Many clinical studies have been done with experimental drugs in the hope of finding one that will prevent, or even shorten, the common cold; none have met with success. However, a new study on the overall frequency of colds has shown the benefits of fitness in this respect. Scientists from Seattle published the results in the American Journal of Medicine; here's a summary of their findings.

What was done

Postmenopausal women in the Seattle area who were overweight or obese, nonsmoking, and sedentary were enrolled between 1998 and 2000. They were randomly assigned to an exercise group or a control (stretching) group. The exercise prescription was at least 45 minutes of moderate intensity exercise 5 days a week, for 12 months. The controls attended a 45-minute stretching session once weekly for the same period.

Questionnaires were administered at baseline, and 3, 6, 9, and 12 months, enquiring about the number of episodes of allergies, upper respiratory tract infections (colds and flu), and other infections during the previous 3 months. All participants were instructed in the common symptoms of colds, flu, and allergies, so that they could distinguish between them.

What was found

There were 115 participants in the study - 53 exercisers and 62 controls. The two groups were strictly comparable; their average age was 61, their average BMI was 30 (i.e. they were borderline overweight or obese), and 88% were white. The exercisers worked out for an average of 3.8 days a week - 85% of the goal.

The average number of colds in the three months before baseline were 0.37 (exerciser group) and 0.29 (control group); average numbers for any respiratory infections were 0.57 (exercisers) and 0.38 (controls). However, it's possible that these numbers were artificially high because the participants weren't trained about the symptoms until baseline.

Over 12 months, the risk of colds decreased significantly in the exercisers compared with the controls:

Total number of colds	Exercisers (53 people)	Controls (62 people)
none	26	19
1	11	15
2	3	13
3	2	2

In the final 3 months of the study the risk of colds in the controls was more than 3-fold higher than in the exercisers.

There was no statistically significant difference between the two groups in the number of upper respiratory tract infections overall, which included flu episodes and other infections.

What the findings may mean

These results show that moderate exercise over the course of a year can reduce the incidence of common colds in postmenopausal women. But why weren't the numbers of all upper respiratory tract infections reduced as well? The researchers explain that this may be because more of the controls were vaccinated against influenza in the 6 months leading up to the study - 20 of them compared with 10 of the exercisers. Moreover, 26 of the controls had a flu shot during the 12-month study compared to 12 of the exercisers. It's possible, also, that susceptibility to colds, in contrast to flu, can be more easily modified by exercise-enhanced host immunity.

The authors of the report suggest that the beneficial effect of exercise may be mediated through a temporary increase in white blood cell counts. Alternatively, exercise can increase immunoglobulin-A in saliva, which is a key component of immunity of the mucosa, the route by which viruses can get into the body. Whatever the mechanism, the result seems clear-cut; moderate exercise helped these women avoid one or two colds. It's another benefit of exercise that shouldn't be overlooked.

Source

• Moderate-intensity exercise reduces the incidence of colds among postmenopausal women. J. Chubak, A. McTiernan, B. Sorensen,  et al., Am J Med, 2006, vol. 119, pp. 937--942

Related Links
Regular Exercise Boosts Effectiveness of 'Flu Shot
Exercise May Boost Immunity
Consistent Exercise Keeps Older Women "Functioning" Well

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