Effect of Vitamin D Serum Levels and Supplementation on Atopic Dermatitis: A Systematic Review and Meta-analysis

Background Previous studies have shown that serum 25-hydroxyvitamin D (25(OH)D) may be associated with atopic dermatitis (AD), and that vitamin D (VD) supplementation may decrease AD severity. Objective The aim of this study was to investigate the association between serum 25(OH)D level and AD, and the effect of VD supplementation on AD severity, while providing stratified analyses based on latitude and region. Methods A systematic review was performed on all published studies in MEDLINE, Embase, and Cochrane Library databases that analyzed effects of serum 25(OH)D and VD supplementation on AD. Results This systematic review and meta-analysis includes 20 studies with 1882 cases of AD. We found significantly lower 25(OH)D levels in AD patients compared with healthy controls (HC) (p < 0.001), significantly lower 25(OH)D levels in severe AD compared with both mild and moderate AD (p < 0.001), and VD supplementation improved AD symptoms (p < 0.001). Limitations Factors like seasonal and environmental changes, sunlight exposure, and cultural practices may confound the relationship between serum 25(OH)D and AD severity. There are limited randomized controlled trials that assess this association. Conclusion Overall, lower serum 25(OH)D is associated with more severe AD, and VD supplementation may help lower AD severity. Further research is needed to confirm the presence and direction of causality of the relationship between VD and AD pathogenesis.