 The goal of this clinical trial is to investigate the therapeutic role of vitamin D supplementation in a subset of patients with atopic dermatitis AD: children with disease onset or worsening in the winter. The investigators hypothesis is that 1 vitamin D supplementation in patients with either wintertime onset or exacerbation of AD will improve Eczema Area and Severity Index EASI scores, and 2 vitamin D supplementation will improve the Investigators Global Assessment. 