title: Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren.
abstract: 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.
  
  
  METHODS
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Division of Molecular Epidemiology, Jikei University School of Medicine, Nishi-shimbashi 3-25-8, Minato-ku, Tokyo 105-8461, Japan. urashima@jikei.ac.jp
authors.forename: Mitsuyoshi
authors.initials: M
authors.lastname: Urashima
authors.forename: Takaaki
authors.initials: T
authors.lastname: Segawa
authors.forename: Minoru
authors.initials: M
authors.lastname: Okazaki
authors.forename: Mana
authors.initials: M
authors.lastname: Kurihara
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Wada
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ida
mesh_terms: D000293:Adolescent; D001827:Body Height; D001835:Body Weight; D002648:Child; D002762:Cholecalciferol / Q000008:administration & dosage* / Q000009:adverse effects / Q000627:therapeutic use; D019587:Dietary Supplements; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D009980:Influenza A virus; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control*; D007564:Japan / Q000453:epidemiology; D008297:Male; D018579:Patient Selection; D010919:Placebos; D012306:Risk
chemical_list: D010919:Placebos; D002762:Cholecalciferol