Abstract
RATIONALE: Low vitamin D levels are associated with asthma and decreased airway responsiveness. Treatment with inhaled corticosteroids improves airway responsiveness and asthma control. OBJECTIVES: To assess the effect of vitamin D levels on prebronchodilator FEV(1), bronchodilator response, and responsiveness to methacholine (PC(20), provocative concentration of methacholine producing a 20% decline in FEV(1)) in patients with asthma treated with inhaled corticosteroids. METHODS: We measured 25-hydroxyvitamin D levels in the serum of children with persistent asthma at the time of enrollment in the Childhood Asthma Management Program. We divided subjects into the vitamin D sufficiency (>30 ng/ml), insufficiency (20-30 ng/ml), and deficiency (<20 ng/ml) groups. Covariates included age, treatment, sex, body mass index, race, history of emergency department visits, hospitalizations, and season that vitamin D specimen was drawn. Our main outcome measures were change in prebronchodilator FEV(1), bronchodilator response, and PC(20) from enrollment to 8-12 months. MEASUREMENTS AND MAIN RESULTS: Of the 1,024 subjects, 663 (65%) were vitamin D sufficient, 260 (25%) were insufficient, and 101 (10%) were deficient. Vitamin D-deficient subjects were more likely to be older, African American, and have a higher body mass index compared with the vitamin D-sufficient and insufficient subjects. In the inhaled corticosteroid treatment group, prebronchodilator FEV(1) increased from randomization to 12 months by 140 ml in the vitamin D-deficient group and prebronchodilator FEV(1) increased by 330 ml in the vitamin D insufficiency group and by 290 ml in the vitamin D sufficiency group (P = 0.0072), in adjusted models. CONCLUSIONS: In children with asthma treated with inhaled corticosteroids, vitamin D deficiency is associated with poorer lung function than in children with vitamin D insufficiency or sufficiency.