Exercise, Vitamins and Respiratory Tract Infections

Abstract

Chubak et al. 1 reported that moderate intensity exercise training reduced common cold incidence but had no effect on the total incidence of upper respiratory infections. As a motivation for the trial, they cited two randomized 3-4 month trials 2,3 which, however, did not find statistically significant effect on upper respiratory infection incidence from moderate exercise, but the studies were small (N 36).In their paper, Chubak et al. failed to refer to our study analyzing the relation between physical activity and common cold incidence in middle-aged Finnish men of the ATBC Study cohort (N = 14,401). Physical activity at work and at leisure had no association with common cold incidence. 4 In Chubak's trial, less severe upper respiratory infections were classified as "the common cold", and the remaining episodes included "flu" and were, on average, more severe. 1 The etiology of these two groups is largely overlapping, but the difference in severity is important. There was no significant difference in the sum of episodes between the two treatment groups. However, according to Table 2, the severity of upper respiratory infections was considerably dissimilar in the two intervention groups. In the exercising group, the proportion of episodes classified as "the common cold" was 35% (23/65), whereas it was significantly higher in the stretching group, 67% (47/70) (P[2-t]=0.0004, Fisher's test). Consequently, the more severe episodes were substantially more frequent in the exercising group (65% vs. 33%), suggesting that exercise might, in fact, have caused harm by making upper respiratory infections more severe.Finally, Chubak et al. mentioned the possibility that vitamins might affect the immune system, but they did not refer to controlled trials with physically active people. In the ATBC Study cohort, vitamin E had no effect on common cold incidence in those who had heavy physical activity at work or at leisure. 4,5 Nevertheless, in six placebo-controlled trials with participants under heavy acute physical stress (combined N = 642), vitamin C reduced common cold risk by 50% (95% CI: 34% to 62%). 5,6 Four of the trials studied marathon runners and thus the latter finding should be generalized cautiously.

Conclusions about intervention effects should not be based on surrogate end points

“…These findings with clinically relevant outcomes thus contradict the surrogate-based proposal by Bruno et al that smokers would benefit of higher vitamin E intakes and it would seem necessary for them to consume at least 15 mg/day of vitamin E [3]. Furthermore, the current US RDA recommendation level for vitamin E, 15 mg/day, is not based on any clinically relevant outcome either and is arbitrary [6]. The divergence in the effects of vitamin E supplementation in the ATBC Study cohort indicates that caution should be maintained in any proposals that people should increase their consumption of vitamin E until its effects are better understood.…”

Vitamin C for the common cold should not be rejected on the basis of old and erroneous articles

“…They discussed the technical aspects of certain studies, but in most cases they did not present the original results, thereby hampering the reader in drawing his or her own conclusions about the trial results. 6,7 They uncritically accepted Karlowski et al's placebo effect explanation, 2 although careful reading of the report would have shown that it is not valid. There are many further problems in the Dykes and Meier review, 3 as described elsewhere.…”

“…[4][5][6] The authors argued that the results of their placebo controlled double-blind trial might be explained, paradoxically, by the placebo effect. However, their suggestion was based on a subgroup analysis in which they excluded 42% of recorded common cold episodes without any justification.…”

“…Thus their placebo effect explanation can be confidently rejected. [4][5][6] Karlowski et al 2 had 4 arms in their trial: A, placebo; B, 3 g/d vitamin C regularly over the trial; C, 3 g/d therapeutic vitamin C when a participant caught a cold; and D, both regular and therapeutic administration so that the dose was 6 g/d during the cold episodes. The results were consistent with dose dependency: the duration of colds in the 6 g/d arm was reduced twice as much as in the 3 g/d arms.…”

“…There are many further problems in the Dykes and Meier review, 3 as described elsewhere. 6,7 The coverage of Mainardi et al's review 1 is wide, and they could not properly discuss the extensive literature on vitamin C and the common cold on the basis of original trial reports.…”