Vitamin C Supplementation and Respiratory Infections: a Systematic Review

Military Medicine, Nov 2004 by Hemilä, Harri

Niemi22 failed to describe properly the technical aspects of his trial with military recruits in two garrisons in Southern Finland. The number of observed common cold episodes was small, leading to low statistical power to observe moderate treatment effects. The low dosage of vitamin C did not reduce the number of common cold episodes.

Trials with Students in Crowded Lodgings and with Marathon Runners

For this review, the most essential criteria among military recruits are their age and the crowded nature of their accommodations, which regularly subjects them to close contact with each other. Three vitamin C trials with students residing in closed and crowded lodgings share these same criteria (Table II). An additional criterion typical of military recruits is their frequent heavy physical exertion, which arises interest in trials with marathon runners as well (Table II).

Glazebrook and Thomson23 carried out a large-scale trial with male students (15-20 years old) in a boarding school in Scotland. For practical reasons, the participants were not randomly allocated to the study groups, but certain administrative divisions occupying the same tables in the dining room were served vitamin C-supplemented food, whereas others remained as controls. There was, however, a fair amount of mixing of the dining divisions in the sleeping quarters. The authors reported that a tonsillitis epidemic affected all of the dining divisions uniformly the year before, suggesting that the divisions should not be regarded as separate units. Because vitamin C was added to the food in the kitchen, the placebo effect does not seem a relevant concern, although no placebo powder was used. Vitamin C supplementation continued even when a student fell so ill that he was admitted to the hospital.

Glazebrook and Thomson23 found a statistically significant, but clinically minor, reduction in common cold incidence by vitamin C, but they observed a greater effect in the number of youths hospitalized for severe colds. In the control group, 23.0% of participants were admitted to the hospital because of severe colds, whereas in the vitamin C group, only 17.6% of participants were hospitalized for colds. Accordingly, 5.4% of vitamin C subjects obtained benefit for this outcome. There was no difference in the incidence of streptococcal infections, but fewer vitamin C participants were hospitalized, and their stay at the hospital was on average significantly shorter than those in the control group. Finally, no cases of pneumonia or rheumatic fever occurred in the vitamin C group, whereas several cases occurred in the control group. Although this was not a doubleblind, placebo-controlled trial, the placebo effect and information bias28 fail to explain easily the findings for the hospital stay or the dramatic difference in the incidence of pneumonia and rheumatic fever. In particular, the duration of treatment in the hospital was completely beyond the authors' control.

Ritzel7,24 performed a short, randomized, double-blind, placebo-controlled trial with male high school students (15-17 years old) at a skiing camp in the Swiss Alps. Vitamin C significantly reduced the incidence and duration of colds. Furthermore, the vitamin C group saw substantially fewer days with constitutional symptoms.