The association between serum vitamin D levels and urticaria: a meta-analysis of observational studies

INTRODUCTION: Despite the recent studies revealed Vitamin D may play a role in urticaria, no meta-analysis providing definite conclusions in this field has been reported. EVIDENCE ACQUISITION: A systematic search up to June 30th, 2017 was conducted in MEDLINE (via PubMed) and Excerpta Medica database (EMBASE) to identify relevant articles. Search terms included "vitamin D'' or "25-hydroxyvitamin D" or "25-hydroxy-vitamin D" or "25(OH) D" or "1,25-dihydroxyvitamin D" combined with "urticaria." EVIDENCE SYNTHESIS: Initial searches yielded 30 citations. Of these original results, 10 met specific selection criteria and were included in the meta-analysis with 547 urticaria cases and 517 controls. Vitamin D levels were significantly decreased in the urticarial cases (WMD -9.8 mg/L, 95% CI: -12.57 to -7.04 mg/L, from a random effects model), with a significant heterogeneity (I-2=85.9%, P=0.000). When divide the Vitamin D level into two subgroups, the pooled OR comparing vitamin D insufficiency vs. normal level was 1.64 (95% CI: 0.71 to 3.77). Meanwhile, vitamin D deficiency vs. normal level was 4.09 (95% CI: 1.32 to 12.73). CONCLUSIONS: The study demonstrated that patients with urticaria had a lower Vitamin D level than healthy controls. Vitamin D deficiency rather than insufficiency has a positive relationship with urticaria. However, larger-scale studies with a longer duration of treatment are needed to confirm this conclusion.