Vitamin D and Severe Asthma Exacerbations

Inclusion Criteria: * Be at least 6 years of age and younger than 15 years of age * Have physician-diagnosed asthma * Taking a medium dose of ICS (e.g. fluticasone 220mcg BID) for daily asthma control for at least 6 months in the prior year. * Have had a severe asthma exacerbation in the previous year, defined as an Emergency Department (ED) visit, hospitalization, or unscheduled clinic visit for asthma resulting in intramuscular, intravenous, or oral steroids. * Have bronchodilator responsiveness (BDR, an increase in FEV1 ≥12% from baseline after administration of inhaled albuterol) or (if no BDR) increased airway responsiveness to methacholine challenge * Have vitamin D insufficiency (a serum vitamin D (25(OH)D) level \<30 ng/ml) * Have his/her parents give voluntary written consent to participate in the study Exclusion Criteria: * Chronic respiratory disorder other than asthma (e.g., bronchiectasis). * Severe asthma, as evidenced by any of the following: a) chronic need for medication other than single controller therapy and inhaled β2-agonist, b) intubation for asthma at any time, and c) ≥2 hospitalizations or ≥6 severe asthma exacerbations in the previous year * History of cigarette smoking in the prior year or former smoking if ≥5 pack-years * Hepatic or renal disease, metabolic rickets, malabsorptive disorders, or other chronic diseases that would affect vitamin D metabolism * Immune deficiency, cleft palate or Down's syndrome, which might increase the child's likelihood of respiratory infections * Treatment with anticonvulsants or pharmacological doses of vitamin D (≥1,000 IU/day of vitamin D2 or D3) * Chronic oral corticosteroid therapy * Inability to perform acceptable spirometry * Use of investigational therapies or participation in clinical trials 30 days before or during the duration of the study * Serum calcium \>10.8 mg/dl * Serum 25(OH) D \<10 ng/ml (severe vitamin D deficiency)