Study of the Effect of Vitamin D as an Add-on Therapy to Corticosteroids in Asthma

This is a randomized, double-blind parallel group trial that will enroll individuals who have vitamin D insufficiency and asthma with persistent symptoms despite low-dose inhaled corticosteroid. Participants on low-dose inhaled corticosteroid will be randomized to add-on therapy with either placebo or high-dose vitamin D for a 28-week period. During the inhaled corticosteroid-stable phase, participants will remain on low-dose inhaled corticosteroid. During the inhaled corticosteroid-taper phase, participants will taper their inhaled corticosteroid by 50% at two time-points post-randomization. The investigators will determine if the addition of vitamin D reduces the likelihood of treatment failure when compared to placebo during both the inhaled corticosteroid-stable and inhaled corticosteroid-taper phases of the study. Given the high prevalence of both vitamin D insufficiency and asthma, this trial has high potential to impact daily asthma management.