Molecular insights into the role of vitamin D in atopic dermatitis: pathogenesis, diagnosis, and emerging therapies.

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by skin barrier dysfunction, immune dysregulation, and microbial imbalance. Increasing evidence suggests that vitamin D, a secosteroid hormone with pleiotropic effects, plays a key role in modulating the pathogenesis of AD. This review provides a comprehensive overview of the molecular mechanisms through which vitamin D influences skin integrity and immune function, focusing on vitamin D receptor-mediated pathways, genetic and epigenetic modifiers, and the interplay with immune cells and microbiota. We also examine the epidemiological correlations between vitamin D deficiency and AD prevalence, diagnostic considerations including biomarkers and serum 25-hydroxyvitamin D evaluation, and therapeutic strategies involving systemic and topical vitamin D interventions. The review further discusses ongoing controversies regarding optimal dosing and evaluates the limitations of current clinical evidence. Finally, emerging research directions, such as vitamin D-microbiota-skin axis and personalized vitamin D therapy, are proposed as promising avenues for advancing AD management.