The genetic polymorphisms in vitamin D receptor and the risk of type 2 diabetes mellitus: an updated meta-analysis.

BACKGROUND AND OBJECTIVES: Vitamin D receptor (VDR) genetic polymorphisms are considered to be associated with type 2 diabetes mellitus (T2DM), but this is inconclusive. The aim of this study is to quantify the association between polymorphisms of BsmI and FokI in the VDR gene and T2DM risk through literature review. METHODS AND STUDY DESIGN: Original articles published from 1999 to June 2014 were discovered through PubMed, ISI Web of Science, China National Knowledge Infrastructure, Chinese Wanfang Database, and the Chinese Biomedical Literature Database. The pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated with software STATA version 12.0. RESULTS: Twenty-three articles containing 30 case-control studies were included. The association between the BsmI polymorphism and T2DM was weak in two genetic models (Bb vs bb and BB+Bb vs bb). The subgroup analysis showed that this association was only found in the studies with a small sample size (<200). A strong association between FokI polymorphism and T2DM indicated that this gene polymorphism was possibly a risk factor for T2DM (ff vs FF: OR=1.57, 95% CI: 1.28-1.93, p<0.001; Ff vs FF: OR=1.54, 95% CI: 1.31-1.81, p<0.001; ff+Ff vs FF: OR=1.57, 95% CI: 1.35-1.83, p<0.001), especially in Chinese populations. CONCLUSION: More reliable conclusions about associations between VDR genetic polymorphisms and T2DM will depend on studies with larger sample size and by ethnicity.