[Note: an important distinction, Dr. Urashima commented to the press, is that "vitamin D naturally enhances innate immunity while vaccine enhances acquired immunity."]
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 https://center.umin.ac.jp 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: firstname.lastname@example.org]