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Fred Hutchinson Cancer Research Center, Cancer Prevention Program, Seattle, WashDepartment of Epidemiology, University of Washington, Seattle, WashDepartment of Medicine, University of Washington, Seattle, Wash
Requests for reprints should be addressed to Cornelia Ulrich, PhD, Fred Hutchinson Cancer Research Center, Cancer Prevention Program, 1100 Fairview Ave N, M4-B402, PO Box 19024, Seattle, WA 98109-1024.
Our aim was to assess the effect of a moderate-intensity, year-long exercise program on the risk of colds and other upper respiratory tract infections in postmenopausal women.
Subjects
A total of 115 overweight and obese, sedentary, postmenopausal women in the Seattle area participated.
Methods
Participants were randomly assigned to the moderate-intensity exercise group or the control group. The intervention consisted of 45 minutes of moderate-intensity exercise 5 days per week for 12 months. Control participants attended once-weekly, 45-minute stretching sessions. Questionnaires asking about upper respiratory tract infections in the previous 3 months were administered quarterly during the course of the year-long trial. Poisson regression was used to estimate the effect of exercise on colds and other upper respiratory tract infections.
Results
Over 12 months, the risk of colds decreased in exercisers relative to stretchers (P = .02): In the final 3 months of the study, the risk of colds in stretchers was more than threefold that of exercisers (P = .03). Risk of upper respiratory tract infections overall did not differ (P = .16), yet may have been biased by differential proportions of influenza vaccinations in the intervention and control groups.
Conclusions
This study suggests that 1 year of moderate-intensity exercise training can reduce the incidence of colds among postmenopausal women. These findings are of public health relevance and add a new facet to the growing literature on the health benefits of moderate exercise.
The role of regular physical activity in preventing acute illnesses such as colds or other upper respiratory tract infections is not well defined. Improving our understanding of how to prevent these illnesses may help reduce the economic and health burden they impose. With adults in the United States reporting, on average, two to four colds per year,
Respiratory symptoms in relation to residential coal burning and environmental tobacco smoke among early adolescents in Wuhan, China: a cross-sectional study.
Research suggests that regular, moderate-intensity physical activity protects against upper respiratory tract infections, but this relationship has not been well established.
•
We randomized postmenopausal women to a 1-year exercise training intervention program or stretching control group.
•
The probability of self-reported colds was significantly decreased among exercisers compared with stretchers over the course of the year.
•
Results from this randomized trial show that postmenopausal women can reduce their risk of colds by engaging in moderate-intensity exercise.
Research suggests a J-shaped relationship between exercise and the risk of upper respiratory tract infections. Several randomized trials have suggested that moderate-intensity training reduces the severity of upper respiratory tract infections;
The short-term randomized studies that have been conducted to date suggest a relationship between exercise training and the duration of upper respiratory tract infections.
Yet they have not been able to address whether exercise training can affect the number (incidence) of upper respiratory tract infections. Thus, the objective of the present study was to assess, in a randomized, controlled trial with excellent adherence, the effects of a year-long exercise intervention on the risk of colds and other upper respiratory tract infections.
Methods
Participants were enrolled in a randomized trial of Seattle-area, overweight/obese, nonsmoking, sedentary, postmenopausal women,
recruited between 1998 and 2000, who met eligibility criteria for a study of the exercise effect on immune function (n=115, described in detail in Shade et al.
). The exercise prescription consisted of at least 45 minutes of moderate-intensity exercise 5 days per week for 12 months (for details, see Irwin et al.
). Control participants attended once-weekly, 45-minute stretching sessions. All participants were asked to maintain their usual diet and exercise habits. Participants provided written informed consent, and the institutional review board approved all study procedures.
At baseline and 3, 6, 9, and 12 months, participants completed self-administered questionnaires, modified from established, validated instruments,
on the number of episodes of allergies, upper respiratory tract infections (colds and flu), and other infections over the past 3 months. Before randomization, women were taught to monitor the occurrence of upper respiratory tract infections and instructed in questionnaire completion and how to distinguish among allergies, colds, and flu. Specifically, subjects were provided the following guidelines: Allergy symptoms include a runny nose, itchy eyes, and clear discharge from nose. They are not accompanied by a severe sore throat or cough and usually persist for more than 2 weeks. Symptoms may worsen with exposure to house dust, pollen, or pets. Cold symptoms include a runny or stuffy nose, sore throat, coughing, sneezing, and clear or colored discharge. Flu symptoms include fever, general aches and pains, headache, fatigue and weakness, chest discomfort, and cough. These instructions were partially repeated on the questionnaire (see Appendix in the online version of the Journal).
Using these guidelines, women recorded the number and self-defined type of upper respiratory tract infections they experienced during the past 3 months, including whether they visited a physician for diagnosis. We evaluated questionnaire reproducibility among 43 study participants by repeat administration within 5 weeks of the initial response. Thirty-nine (91%) of the selected women returned the repeat questionnaire. Concordance with respect to reporting of upper respiratory tract infections episodes was 74% (κ=0.44).
At baseline, 3 months, and 12 months, we collected demographic information, medical history, health habits, reproductive history, physical activity, diet, and anthropometric variables.
Some participants were missing data on colds or other upper respiratory tract infection episodes at 6 and 9 months because no clinic visit took place at that point (44/460 possible assessments were missing, <10%). We addressed this issue of sporadically missing data by using Poisson regression, which allowed for use of data from all available time-points without eliminating individuals with some missing data. Outcomes were modeled as a function of intervention group; indicator variables for 6, 9, and 12 months; and interaction terms between intervention group and each time-point indicator. Colds or other upper respiratory tract infection episodes reported at each visit were considered repeated measures, and we therefore used a generalized estimating equation modification of the Poisson regression model.
We assumed an unstructured working correlation matrix, computed robust standard errors, and performed an intention-to-treat analysis, with P≤.05 being considered statistically significant. Results were identical or stronger when restricted to women who had assessments at all four time-points. We also evaluated whether the exercise effect differed by age (<60 vs ≥60 years) or regular multivitamin use, assessed by abstraction of vitamin bottles brought into the clinic at baseline (see Shade et al.
for details). All analyses were performed using SAS 8.0 (SAS Institute, Cary, NC) and Stata 8 (StataCorp, College Station, Tex) statistical software. All P values are 2-sided.
Results
Exercisers and stretching controls were comparable at baseline on key demographic variables and self-reported colds and other upper respiratory tract infection episodes (Table 1). On average, study participants were 61 years old and had a body mass index of 30 kg/m2. Intervention participants exercised an average of 3.8 days/week, for a total of 166 minutes/week, meeting 85% of their exercise time goal. Exercisers wore heart-rate monitors and showed significant increases in cardiopulmonary fitness (VO2 max).
Reporting of colds and other upper respiratory tract infections episodes in the 3 months before the baseline visit may be artificially high because of lack of instruction in how to track qualifying episodes.
0
25 (66)
30 (71)
1
12 (32)
12 (29)
2
1 (3)
0 (0)
Mean (SD)
0.37 (0.54)
0.29 (0.46)
Number of any upper respiratory tract infections in 3 mo before baseline
Reporting of colds and other upper respiratory tract infections episodes in the 3 months before the baseline visit may be artificially high because of lack of instruction in how to track qualifying episodes.
0
18 (49)
27 (64)
1
17 (46)
14 (33)
2
2 (5)
1 (2)
Mean (SD)
0.57 (0.60)
0.38 (0.54)
Any allergy episodes
7 (18)
7 (17)
Received influenza immunization
a) in previous 6 mo
10 (19)
20 (32)
b) during the intervention period
12 (23)
26 (42)
SD = standard deviation.
*None of the differences are statistically significant at the α=0.05 level, except for influenza immunization.
† Reporting of colds and other upper respiratory tract infections episodes in the 3 months before the baseline visit may be artificially high because of lack of instruction in how to track qualifying episodes.
The exercise intervention decreased the risk of self-reported colds relative to controls (Figure 1). Over 12 months, the risk of colds decreased modestly in exercisers and increased modestly in stretchers (Figure 1, P=.02 for overall difference). In the final 3 months of the study, the risk of colds in stretchers was more than 3-fold higher than that of exercisers (P=.03). More stretchers than exercisers had at least one cold during the 12-month study period (48.4% vs 30.2%), and among women reporting at least one cold, stretchers tended to report colds more frequently than exercisers (Table 2). No statistically significant exercise effect was observed for upper respiratory tract infections overall, which included flu episodes and unknown types of upper respiratory tract infections (P = .16).
Figure 1Number of colds in postmenopausal exercisers and stretchers assessed quarterly throughout the 12-month intervention period.
The total possible number of assessments was 212 for exercisers and 248 for stretchers (four time-points multiplied by the number of individuals). In exercisers, 9.4% of assessments were missing, compared with 9.7% in stretchers.
P values for overall difference between exercise and stretching groups during the entire intervention period based on Poisson regression, which includes persons who have data missing at one or more time-points.
P values for overall difference between exercise and stretching groups during the entire intervention period based on Poisson regression, which includes persons who have data missing at one or more time-points.
P values for overall difference between exercise and stretching groups during the entire intervention period based on Poisson regression, which includes persons who have data missing at one or more time-points.
P values for overall difference between exercise and stretching groups during the entire intervention period based on Poisson regression, which includes persons who have data missing at one or more time-points.
0.16
0.57
0.16
P = .20 for interaction
RR = relative risk; CI = confidence interval.
The total possible number of assessments was 212 for exercisers and 248 for stretchers (four time-points multiplied by the number of individuals). In exercisers, 9.4% of assessments were missing, compared with 9.7% in stretchers.
† P values for overall difference between exercise and stretching groups during the entire intervention period based on Poisson regression, which includes persons who have data missing at one or more time-points.
‡ Includes colds, flu, unknown, and other upper respiratory tract infections.
Exercise reduced the risk of colds in multivitamin nonusers (P = .02), whereas there was a suggested increase in users (P = .07). However, this difference in effects between the two groups was not statistically significant (P=.11 for the interaction). We did not observe significant differences in the exercise effect by age group (results not shown).
Discussion
The results from this randomized, controlled trial show that moderate-intensity exercise training over the course of 1 year can reduce the incidence of colds among postmenopausal, nonsmoking, previously sedentary women. The lack of effect on upper respiratory tract infections overall (which included flu episodes) may be because more stretchers than exercisers were vaccinated against influenza in the 6 months before baseline. Further, more stretchers (42%) than exercisers (23%) reported vaccination during the intervention period (P = .03). In addition, it is possible that susceptibility to colds, in contrast to influenza, may be more easily modifiable by host immunity. Although it seems that differences in the risk of colds between exercisers and stretchers in our study were partly attributable to an increase in colds in stretchers, this increase was not statistically significant. Attending exercise or stretching classes on a regular basis may increase exposure to infectious agents as the result of social contacts, and thus the decrease among exercisers may be even more relevant.
The long duration of our trial enabled us to investigate whether exercise can reduce the number (incidence) of upper respiratory tract infection and cold episodes. Unfortunately, the current design did not permit the measurement of upper respiratory tract infections by daily health-logs, as used in past research
because of participant burden. A previous cross-sectional study on upper respiratory tract infections that compared highly conditioned individuals with those randomized to walking or calisthenic exercise found the incidence of upper respiratory tract infections to be significantly less common among highly conditioned individuals, with walkers and calisthenic exercisers having the intermediate and highest risk of upper respiratory tract infections, respectively.
In that study, review of the symptoms revealed that the upper respiratory tract infection cases could be almost exclusively described as the common cold. Thus, our results, which show an effect specifically for colds, are consistent with these past investigations.
Brisk walking amounted to 51.8% of facility-based and 73.7% of home-based activity among exercisers.
showed that walking for 30 minutes can increase leukocyte counts temporarily and suggested that walking may reduce the risk of upper respiratory tract infections by increasing the number of episodes in which leukocytes counts are transiently higher. Another possible mechanism is through an increase in salivary immunoglobulin (Ig) A, a key component of mucosal immunity. An inverse relationship between salivary IgA concentration or secretion rate and the risk of upper respiratory tract infections in athletes has been described.
suggest that salivary IgA levels increase after engaging in a moderate-intensity exercise program for several months. However, findings from studies comparing active individuals with sedentary individuals are inconsistent, as are studies evaluating serum IgA.
In our study, the protective exercise effect seemed confined to women who did not regularly use multivitamins. Several epidemiologic studies suggest that multivitamin use may be immune-enhancing, although the data from randomized, controlled trials are not entirely consistent.
Effect of multivitamin and multimineral supplements on morbidity from infections in older people (MAVIS trial): pragmatic, randomised, double blind, placebo controlled trial.
Role of multivitamins and mineral supplements in preventing infections in elderly people: systematic review and meta-analysis of randomised controlled trials.
Our findings suggest that women who do not use multivitamins may derive greater protection against colds from exercise.
The present study has several strengths, including its relatively long intervention period and large size compared with previous studies. Further, adherence was excellent. We do, however, note several limitations. Because participants did not keep daily logs of infections and allergies, reliance on memory may have introduced error. The reproducibility of the occurrence of episodes was good, whereas the self-reported duration of such episodes did not prove reproducible in this setting and thus could not be evaluated. Participants may not have classified colds, flu, and other upper respiratory tract infections accurately; however, both exercisers and stretching controls received identical instructions, and any error in the reporting should have biased our findings toward observing no effect.
Our trial is the first to report on the effects of a year-long, moderate-intensity exercise training program on the incidence of upper respiratory tract infections. Although we did not find an effect overall on upper respiratory tract infections, our study suggests that moderate-intensity training can reduce the risk of colds in postmenopausal, nonsmoking, overweight or obese women. This finding is of clinical relevance and adds a new facet to the growing literature on the health benefits of moderate exercise.
Respiratory symptoms in relation to residential coal burning and environmental tobacco smoke among early adolescents in Wuhan, China: a cross-sectional study.
Effect of multivitamin and multimineral supplements on morbidity from infections in older people (MAVIS trial): pragmatic, randomised, double blind, placebo controlled trial.
Role of multivitamins and mineral supplements in preventing infections in elderly people: systematic review and meta-analysis of randomised controlled trials.
This study was supported by a grant from the National Cancer Institute (NCI) (R01 CA 69334). Ms. Chubak was supported by grant T32 CA09168 from the NCI. The contents of this publication are solely the responsibility of the authors and do not necessarily represent the official views of the NCI or National Institutes of Health. Dr. Wener was supported in part by the University of Washington Clinical Nutrition Research Grant (DK35816).
The total possible number of assessments was 212 for exercisers and 248 for stretchers (four time-points multiplied by the number of individuals). In exercisers, 9.4% of assessments were missing, compared with 9.7% in stretchers.
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