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Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren

– Source: American Journal of Clinical Nutrition, Mar 10, 2010

Background: To our knowledge, no rigorously designed clinical trials have evaluated the relation between vitamin D and physician-diagnosed 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 as UMIN000001373.

Source: American Journal of Clinical Nutrition, Mar 10, 2010. PMID: 20219962, by Urashima M, Segawa T, Okazaki M, Kurihara M, Wada Y, Ida H. Division of Molecular Epidemiology Jikei University School of Medicine Minato-ku Tokyo, Japan. [Email:]