A “vitamin D hypothesis” has been proposed to explain the increased prevalence of eczema in regions with higher latitude. This review focuses on the current available evidence with regard to the possible effect of vitamin D on the development of atopic eczema. Observational studies have indicated a link between vitamin D status and eczema outcomes, including lower serum vitamin D levels associated with increased incidence and severity of eczema symptoms. Vitamin D is known to have a regulatory influence on both the immune system and skin barrier function, both critical in the pathogenesis of eczema. However heterogeneous results have been found in studies to date investigating the effect of vitamin D status during pregnancy and infancy on the prevention of eczema outcomes. Well-designed, adequately powered, randomised controlled trials are needed. The study design of any new intervention trials should measure vitamin D levels at multiple time points during the intervention, ultraviolet (UV) radiation exposure via the use of individual UV dosimeters, and investigate the role of individual genetic polymorphisms. In conclusion, the current available evidence does not allow firm conclusions to be made on whether vitamin D status affects the development of atopic eczema.
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