Forno E, Bacharier LB, Phipatanakul W, et al. - This randomized, double-blind, placebo-controlled clinical trial was undertaken to determine if vitamin D₃ supplementation improves the time to a severe exacerbation in children with asthma and low vitamin D levels. Candidates were selected from 7 US centers. The sample consisted of 192 children (mean age, 9.8 years; 77 girls [40%]). Participants (n = 192 children, mean age, 9.8 years; 77 girls [40%]) were randomized to vitamin D₃, 4,000 IU/d (n = 96), or placebo (n = 96) for 48 weeks and maintained with fluticasone propionate, 176 μg/d (6-11 years old), or 220 μg/d (12-16 years old). Vitamin D₃ supplementation, relative to placebo, did not significantly increase the time for severe asthma exacerbation in children with persistent asthma and low levels of vitamin D. The results do not endorse the use of vitamin D₃ supplementation in this group of patients to prevent severe asthma exacerbations.