The Role of Vitamin D in Chronic Urticaria and Angioedema Treatment

This clinical study was designed based on our hypothesis that vitamin D plays an important role in chronic urticaria and that high dose supplementation with vitamin D in subjects with chronic urticaria will improve clinical response. This clinical study will investigate our hypothesis in three Specific Aims: 1. Determine whether high dosing vitamin D supplementation (4000 IU/day) reduces medication usage (primary outcome) and urticaria severity score (secondary outcome) in subjects with chronic urticaria as compared to low dosing (600 IU/day). 2. Determine if high dosing of vitamin D (4000 IU/day) is safe and well-tolerated in subjects with chronic urticaria with or without baseline vitamin D deficiency. 3. Investigate whether there is an association with serum 25-hydroxyvitamin D levels, vitamin D receptor mRNA expression, and chronic urticaria severity.