In recent years, low vitamin D status has been proposed as a putative risk factor for allergic diseases. A growing body of literature reports low vitamin D levels in atopic patients and supports an association between vitamin D deficiency and risk of adverse asthma and allergies outcomes. Therefore, it has been speculated that vitamin D supplementation may either prevent or reduce the risk of allergic diseases. Birth cohort studies addressing the role of vitamin D intake during pregnancy have shown conflicting results regarding allergy outcomes in offspring. Currently, only a few studies have tried to supplement vitamin D in asthmatic patients, often as an add-on therapy to standard asthma controller medications, and results are not all consistent. There is emerging data to show that vitamin D can enhance the antiinflammatory effects of glucocorticoids and potentially be used as adjuvant therapy in steroid-resistant asthma. Recent in vivo data suggest that vitamin D supplementation may also reduce the severity of atopic dermatitis. This review examines the existing relevant literature focusing on vitamin D supplementation in the treatment of allergic diseases
