LETTER Exercise, Vitamins and Respiratory Tract Infections To the Editor: Chubak and colleagues 1 reported that moderate-intensity exercise training reduced common cold incidence but had no effect on the total incidence of upper respiratory infec- tions. As a motivation for the trial, they cited 2 randomized 3- to 4-month trials 2,3 ; however, these trials did not ﬁnd a statistically signiﬁcant effect on upper respiratory infection incidence from moderate exercise, but the studies were small (N  36). In their article, Chubak et al 1 failed to refer to our study analyzing the relation between physical activity and com- mon 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 et al’s trial, 1 less severe upper respiratory infections were classiﬁed as “the common cold,” and the remaining episodes included “ﬂu” and were, on average, more severe. The causes of the illnesses in these 2 groups are largely overlapping, but the difference in severity is important. There was no signiﬁcant difference in the sum of episodes between the 2 treatment groups. However, accord- ing to Table 2 in Chubak et al’s article, the severity of upper respiratory infections was considerably dissimilar in the 2 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] = .0004, Fisher exact test). Consequently, the more severe episodes were substantially more frequent in the exercising group (65% vs 33%), sug- gesting that exercise might, in fact, have caused harm by making upper respiratory infections more severe. Finally, Chubak et al 1 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 6 placebo-controlled trials with participants under heavy acute physical stress (combined N = 642), vitamin C reduced common cold risk by 50% (95% conﬁdence interval: -34% to -62%). 5,6 Four of the trials studied marathon runners; thus, the latter ﬁnding should be generalized cautiously. Harri Hemilä, PhD, MD Department of Public Health University of Helsinki Helsinki, Finland doi:10.1016/j.amjmed.2006.11.025 References 1. Chubak J, McTiernan A, Sorensen B, et al. Moderate-intensity exercise reduces the incidence of colds among postmenopausal women. Am J Med. 2006;119:937-942. 2. Nieman DC, Nehlsen-Cannarella SL, Markoff PA, et al. The effects of moderate exercise training on natural killer cells and acute upper respi- ratory tract infections. Int J Sports Med. 1990;11:467-473. 3. Nieman DC, Henson DA, Gusewitch G, et al. Physical activity and immune function in elderly women. Med Sci Sports Exerc. 1993;25: 823-831. 4. Hemilä H, Virtamo J, Albanes D, Kaprio J. Physical activity and the common cold in men administered vitamin E and -carotene. Med Sci Sports Exerc. 2003;35:1815-1820. 5. Hemilä H. Do vitamins C and E affect respiratory infections? [Disser- tation]. Helsinki, Finland: University of Helsinki; 2006:48-50, 66-67. Available at: http://ethesis.helsinki.ﬁ/julkaisut/laa/kansa/vk/hemila/. Last accessed April 11, 2007. 6. Douglas RM, Hemilä H. Vitamin C for preventing and treating the common cold. PLoS Med. 2005;2:e168. 0002-9343/$ -see front matter © 2007 Elsevier Inc. All rights reserved. The American Journal of Medicine (2007) 120, e17