Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren
Mitsuyoshi Urashima, Takaaki Segawa, Minoru Okazaki, Mana Kurihara, Yasuyuki Wada, Hiroyuki Ida
The American Journal of Clinical Nutrition, doi:10.3945/ajcn.2009.29094
Background: To our knowledge, no rigorously designed clinical trials have evaluated the relation between vitamin D and physiciandiagnosed seasonal influenza. Objective: We investigated the effect of vitamin D supplements on the incidence of seasonal influenza A in schoolchildren. Design: From December 2008 through March 2009, we conducted a randomized, double-blind, placebo-controlled trial comparing vitamin D 3 supplements (1200 IU/d) with placebo in schoolchildren. The primary outcome was the incidence of influenza A, diagnosed with influenza antigen testing with a nasopharyngeal swab specimen. Results: Influenza A occurred in 18 of 167 (10.8%) children in the vitamin D 3 group compared with 31 of 167 (18.6%) children in the placebo group [relative risk (RR), 0.58; 95% CI: 0.34, 0.99; P = 0.04]. The reduction in influenza A was more prominent in children who had not been taking other vitamin D supplements (RR: 0.36; 95% CI: 0.17, 0.79; P = 0.006) and who started nursery school after age 3 y (RR: 0.36; 95% CI: 0.17, 0.78; P = 0.005). In children with a previous diagnosis of asthma, asthma attacks as a secondary outcome occurred in 2 children receiving vitamin D 3 compared with 12 children receiving placebo (RR: 0.17; 95% CI: 0.04, 0.73; P = 0.006).
Conclusion: This study suggests that vitamin D 3 supplementation during the winter may reduce the incidence of influenza A, especially in specific subgroups of schoolchildren. This trial was registered at https://center.umin.ac.jp as UMIN000001373.
and signs of influenza by reducing cytokine secretion. In this study, vitamin D reduced the incidence of influenza A, but not of influenza B. The cytokine secretion pattern can differ between influenza A and influenza B (18) . If vitamin D modulates cytokine secretion, preventive effects of vitamin D may be different between influenza A and influenza B. Because taking vitamin D 3 supplements for 1 y with a dose ranging from 200 to 2000 IU in schoolchildren has been shown to be safe (19) , we set the dose of vitamin D 3 at 1200 IU in this trial. No serious adverse events occurred. It reportedly takes '3 mo to reach a steady state of vitamin D concentrations by supplementation (20) . Thus, December might be theoretically
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