Results from experimental studies, observational studies, two small trials, and a recent meta-analysis suggest that vitamin D reduces the risk of severe asthma exacerbations, and that this protective effect may be due to immune modulation of viral illnesses and/or increased response to inhaled corticosteroids (ICS).~On the basis of those findings, the investigators hypothesize that vitamin D reduces the incidence of severe asthma exacerbations in high-risk school-aged children who have a serum vitamin D level <30 ng/ml and who are being treated with ICS for persistent asthma. The investigators further hypothesize that this protective effect results from reduced incidence of common viral illnesses or enhanced response to ICS. These hypotheses will be tested in a 48-week randomized double-masked placebo-controlled trial of vitamin D3 supplementation to prevent severe asthma exacerbations in 400 children aged 6 to 16 years who have vitamin D insufficiency or deficiency (a serum 25(OH)D <30 ng/ml) and experienced a severe exacerbation in the prior year (a marker of high risk for subsequent events), and who (after a run-in period) are well controlled on medium-dose inhaled corticosteroids.~Our primary aim will determine whether vitamin D3 (4,000 IU/day) reduces the risk of severe asthma exacerbations (our primary outcome) in participating children. Secondary aims will determine the efficacy of vitamin D3 supplementation in: 1) preventing severe asthma exacerbations due to viral infections, 2) reducing the daily and average cumulative dose of inhaled corticosteroids.~Study participation involves 8-9 visits, with each visit lasting between 30-90 minutes. Participation requires completion of study questionnaires, spirometry (breathing tests), and collection of blood samples (to measure vitamin D levels) and urine samples (to measure urinary calcium/creatinine ratios) at some study visits. Since the start of the study, vitamin D levels and urinary calcium/creatinine ratios have been simultaneously measured, to monitor for both vitamin D toxicity and high risk of severe vitamin D deficiency or rickets, which (should they occur) would be managed by a pediatric endocrinologist or a pediatric nephrologist, as appropriate.~All safety data for the study is regularly reviewed by a Data Safety Monitoring Board appointed by the National Heart, Lung and Blood Institute, as well as by the Institutional Review Board of each participating institution. Total study participation will last about one year.
This study will determine whether vitamin D3 prevents severe asthma attacks in children who have a serum vitamin D (25(OH)D) level <30 ng/ml and who are being treated with inhaled corticosteroids for asthma. Half the participants will receive vitamin D3 at a dose of 4,000 IU/day, and the other half will receive placebo.