Vitamin C intake and susceptibility to the common cold.
Although the role of vitamin C in common cold incidence had been studied extensively, the level of vitamin C intake has not been unequivocally shown to affect the incidence of colds. In the present study the six largest vitamin C supplementation (> or = 1 g/d) studies, including over 5000 episodes in all, have been analysed, and it is shown that common cold incidence is not reduced in the vitamin C-supplemented groups compared with the placebo groups (pooled rate ratio (RR) 0.99; 95% CI 0.93, 1.04). Consequently these six major studies give no evidence that high-dose vitamin C supplementation decreases common cold incidence in ordinary people. Nevertheless, the analysis was continued with the hypothesis that vitamin C intake may affect common cold susceptibility in specific groups of people. It was assumed that the potential effect of supplementation might be most conspicuous in subjects with low dietary vitamin C intake. The average vitamin C intake has been rather low in the UK and plasma vitamin C concentrations are in general lower in males than in females. In four studies with British females vitamin C supplementation had no marked effect on common cold incidence (pooled RR 0.95; 95% CI 0.86, 1.04). However, in four studies with British male schoolchildren and students a statistically highly significant reduction in common cold incidence was found in groups supplemented with vitamin C (pooled RR 0.70; 95% CI 0.60, 0.81). Thus, these studies with British males indicate that vitamin C intake has physiological effects on susceptibility to common cold infections, although the effect seems quantitatively meaningful only in limited groups of people and is not very large.
Hemilä
H
H
Department of Public Health, University of Helsinki, Finland.
D000293:Adolescent; D000328:Adult; D001205:Ascorbic Acid / Q000008:administration & dosage*; D002648:Child; D002986:Clinical Trials as Topic; D003139:Common Cold / Q000453:epidemiology / Q000517:prevention & control*; D004198:Disease Susceptibility; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D017211:Treatment Failure
D001205:Ascorbic Acid