Does Exercise Prevent the Common Cold?

potential confounders. We analyzed the relationship between leisure time physical activity and common cold incidence in 3,470 males who were followed up for 2 years. In contrast, the metaanalysis by Lee et al. included only 281 participants. Therefore, our study had much narrower CIs. For example, compared with the sedentary participants (n = 1,198), those who carried out moderate-level physical activity at leisure 3 times per week (n = 268) had a slightly higher incidence of colds with adjusted RR (1.05; 95% CI, 0.96 to 1.16). Such a narrow CI around the null effect is inconsistent with any substantial reduction in common cold incidence by moderate level exercise. Finally, even if Lee’s estimate for the effect of exercise on common cold risk is valid (RR = 0.73), such an effect has no practical importance. Given that adults usually have 2 to 4 colds per year, an average person should exercise for 1 to 2 years to prevent 1 episode of the common cold on the basis of the RR = 0.73 estimate. Lee et al. indicated that regular exercise means having exercise sessions 5 times per week. Assuming that 1 exercise session takes 1 hour, 5 exercise sessions per week for 1 year sums up to 250 hours in total; corresponding to 10 full days. Thus, with an effect of RR = 0.73 a person should exercise a time period corresponding to over 1 week round the clock to prevent 1 episode of the common cold which usually does not last over 1 week and usually only slightly limits functional activities. Thus, more time would be used in the exercise sessions than would be saved from suffering from the cold symptoms. Exercise has a number of beneficial effects and therefore sedentary people should be encouraged to start exercise. However, there is no good evidence that exercise reduces the risk of colds. Exercise should not be encouraged with the argument that it would reduce the risk of colds.