Vitamin D3 Supplementation During Winter Months May Reduce Incidence of Influenza A
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In a group of 334 Japanese schoolchildren, preventive intake of vitamin D3 supplements (1,200 IU/day) during winter and early spring was found to reduce the incidence of seasonal influenza A.
The participants—all 6 to 15 years of age—were randomized to treatment with vitamin D3 or placebo. Participants in both groups were asked to take three tablets twice daily; in the treatment group, each tablet contained 200 IU of vitamin D3. The primary outcome was the incidence of influenza A, diagnosed with influenza antigen testing of a nasopharyngeal swab specimen.
Influenza A occurred in 18 of 167 (10.8%) children in the vitamin D3 group compared with 31 of 167 (18.6%) children in the placebo group (RR, 0.58; 95% CI, 0.34–0.99; P = 0.04). The reduction was more prominent in certain subgroups, including children who had not been taking additional vitamin D supplements (other than the study drug) and children who started nursery school when they were 3 years of age or older. Among participants with asthma, asthma attacks (a secondary study outcome) occurred in 2 children receiving vitamin D3 vs 12 children receiving placebo (RR, 0.17; 95% CI, 0.04–0.73; P = 0.006).
Am J Clin Nutr. 2010;91:1255-60.