Atopic dermatitis is a chronic skin disease characterized by a defective skin barrier, inflammation, and increased propensity for skin infections. Vitamin D is a fat-soluble vitamin that is primarily acquired through local production in the skin after ultraviolet light exposure but can also be obtained through natural and supplemental dietary sources. This randomized controlled trial will examine the effects of vitamin D repletion on atopic dermatitis severity in patients with diagnosed deficiency. The investigators hypothesize that pediatric patients with moderate or severe atopic dermatitis and vitamin D deficiency will have improved cutaneous disease after treatment with high dose as compared to standard dose vitamin D.