Background: Psoriasis is a chronic, autoimmune, inflammatory skin disorder. 25-hydroxy vitamin D [25(OH)D] deficiency may contribute to the pathogenesis of psoriasis through reduction in antiproliferative, anti-inflammatory and antiangiogenic activities. Aim: To evaluate the relationship between circulating 25(OH)D levels and psoriasis, and to determine the correlation between serum/plasma 25(OH)D levels and psoriasis severity. Methods: We performed a meta-analysis to compare serum/plasma 25(OH)D levels between patients with psoriasis and healthy controls (HCs), and to determine the correlation coefficients between circulating 25(OH)D levels and psoriasis severity as assessed by Psoriasis Area and Severity Index (PASI). Results: Ten articles with a total of 571 patients with psoriasis and 496 HCs were included. The 25(OH)D level was significantly lower in the psoriasis group than in the HC group. Subgroup analysis by sample size revealed a significantly lower level of 25(OH)D in the psoriasis group for large (N > 80) but not for small (N < 80) sample sizes. Stratification by adjustment for age and/or sex or sample type revealed a significantly lower 25(OH)D level in the psoriasis group after adjustment for serum but not after nonadjustment for plasma. Meta-analysis of the correlation coefficients revealed a small but statistically significant positive correlation between circulating 25(OH)D levels and PASI. Conclusions: This meta-analysis demonstrated that circulating 25(OH)D levels are lower in patients with psoriasis, and that a small but statistically significant negative correlation exists between 25(OH)D levels and psoriasis severity.
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