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Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren
Double-blind placebo-controlled trial (n=334): vitamin D₃ 1200 IU/day versus placebo over one winter—physician-diagnosed influenza A by antigen testing occurred in 18/167 (10.8%) versus 31/167 (18.6%) children (RR 0.58, 95% CI 0.34–0.99; P=0.04); stronger relative reductions appeared in prespecified subgroups without concurrent vitamin D use.
Design
- Setting: Tokyo-area schoolchildren, Dec 2008–Mar 2009
- Arms: vitamin D₃ 1200 IU/day vs placebo (double-blind)
- Primary outcome: influenza A diagnosed by rapid antigen nasopharyngeal swab
Results (ITT headline)
- Influenza A: 18 / 167 (10.8%) on vitamin D₃ vs 31 / 167 (18.6%) on placebo — RR 0.58 (95% CI 0.34–0.99; P = 0.04)
- Subgroup signals (abstract): larger relative reductions when children were not already taking other vitamin D supplements and when nursery entry was after age 3 y
- Asthma attacks (secondary): 2 / D₃ vs 12 / placebo among children with prior asthma diagnosis (RR 0.17, 95% CI 0.04–0.73; P = 0.006)
Evidence hygiene
- Single-season, single-region paediatric trial—do not equate with Martineau adult ARTI IPD meta-analysis (
martineau-2017-vitamin-d-arti-individual-participant-meta-bmj) or cutaneous vitamin D synthesis from sun exposure trials ondaily-sunlightwithout reading population and endpoint differences.
Publication
Urashima M, Segawa T, Okazaki M, Kurihara M, Wada Y, Ida H. Am J Clin Nutr. 2010 May;91(5):1255-60. PMID 20219962.
Outcomes
- Effect Size (Cohen's d / SMD)Physician-diagnosed influenza A (antigen testing): 18/167 (10.8%) on vitamin D₃ 1200 IU/day vs 31/167 (18.6%) on placebo; RR 0.58 (95% CI 0.34–0.99; P=0.04) over one winter season (Urashima et al. 2010).
- Effect Size (Cohen's d / SMD)Asthma attacks (secondary endpoint) among children with prior asthma diagnosis: RR 0.17 (95% CI 0.04–0.73; P=0.006) for vitamin D₃ vs placebo (Urashima et al. 2010).