LAUSR

To the Editor, In 2014, the International Journal of Rheumatic Diseases published an article written by Khabbazi et al. We read this article with interest. The authors performed a casecontrol study comparing the serum level of 25(OH) vitamin D in 48 patients with Behcet’s disease and 47 healthy individuals. The serum levels of 25(OH) vitamin D were measured using the enzyme-linked immunosorbent assay method. They found that vitamin D levels were significantly lower in patients with Behcet’s disease in comparison with healthy controls. Previous studies have shown conflicting results as to whether low vitamin D levels are associated with Behcet’s disease. Thus, we performed a meta-analysis to evaluate the association between vitamin D levels and Behcet’s disease. Searches were performed in Cochrane Central Register of Controlled Trials, MEDLINE and EMBASE databases up until October 2016. The case control studies which assessed vitamin D levels in patients with Behcet’s disease were included in our study. We estimated pooled standard mean difference of vitamin D levels between Behcet’s patients and control groups using a fixed-effect model. The between-study heterogeneity was quantified using I. Our initial search identified 46 articles. Fifteen studies met the criteria for full-length review. Meta-analysis was conducted from four prospective cohort studies involving 438 participants (206 controls and 232 cases.) The pooled mean difference in serum 25hydroxy vitamin D levels between Behcet’s patients and controls was 0.25 ng/mL (95% CI -0.02-0.52, P = 0.07). The statistical between-study heterogeneity (I) was 99%, P < 0.00001. (Fig. 1) We found there was no statistically significant difference in vitamin D levels between patients with Behcet’s disease and healthy individuals. Interestingly, three studies in the meta-analysis had shown that vitamin D levels were significantly lower in patients with Behcet’s in comparison with healthy controls. However, a study by Faezi et al. demonstrated the opposite results. Low vitamin D levels have been reportedly associated with a variety of autoimmune diseases such as rheumatoid arthritis, Crohn’s disease, systemic lupus erythematous and multiple sclerosis. The exact mechanism underlying the association between vitamin D and autoimmune diseases remains poorly understood. The association between low vitamin D levels and psoriasis might be explained by the hypothesis that vitamin D might modulate or play an important role in the immune response in certain conditions. In conclusion, our meta-analysis demonstrated that there was no statistically significant difference in vitamin D levels between patients with Behcet’s disease and healthy individuals. However, the statistical betweenstudy heterogeneity is inevitably high which is obviously due to inconsistency of findings as we mentioned earlier. High heterogeneity seriously limits our ability to