The Association between Polymorphisms of Vitamin D Metabolic-Related Genes and Vitamin D3 Supplementation in Type 2 Diabetic Patients.

OBJECTIVE: To investigate the effect of single nucleotide polymorphisms (SNPs) of the key genes in vitamin D metabolic pathway on the serum 25(OH)D level after long-term vitamin D3 supplementation and provide a theoretical basis for rational vitamin D3 supplementation in diabetic patients with different genetic backgrounds. METHODS: Patients with type 2 diabetes (T2DM) who met the inclusive criteria were given 800 IU of vitamin D3 daily for 30 consecutive months. Serum 25(OH)D levels was measured at enrollment and every 6 months after enrollment. The average value of four-time measurements represented individual serum 25(OH)D level during vitamin D3 supplementation. Multiplex TaqMan genotyping was used to determine the distribution of eight candidate SNPs in genes of DHCR7, CYP2R1, CYP27B1, CYP24A1, and VDR, which are key genes in the vitamin D metabolic pathway, in diabetic patients. RESULTS: At baseline, the average serum 25(OH)D level was 22.71 ± 6.87 ng/mL, and 17.9% of patients had a ≥30 ng/mL level. During supplementation, the level of 25(OH)D increased significantly at each time point, and the average 25(OH)D level increased to 30.61 ± 5.04 ng/mL; however, there were 44.6% of patients whose serum 25(OH)D levels were still below 30 ng/mL. In the patients with CYP27B1 (rs10877012) G/T genotype, 71.79% achieved sufficient level of 25(OH)D, which was significantly higher than the other two genotypes (P < 0.05). Compared with those with T/T genotype, the RR of the patients with rs10877012 for <30 ng/mL level was 0.544 (95% CI: 0.291-0.917), and the RR after adjusting age and outdoor activity was 0.560 (95% CI: 0.292-0.970). CONCLUSION: The serum 25(OH)D level in patients with diabetes mellitus after long-term vitamin D3 supplementation is associated with CYP27B1 polymorphism. Patients with rs10877012 G/T allele have a better response to vitamin D3 supplementation. TRIAL REGISTRATION: This trial is registered with ChiCTR-IPC-17012657.

Vitamin D Deficiency in Relation to the Risk of Metabolic Syndrome in Middle-Aged and Elderly Patients with Type 2 Diabetes Mellitus.

Vitamin D deficiency is highly prevalent all over the world and dietary intakes of vitamin D are very low in China. In this study we aimed to determine whether vitamin D deficiency is associated with increased risk of metabolic syndrome (MetS) among Chinese type 2 diabetes mellitus (T2DM) patients aged over 50 y. Serum 25-hydroxyvitamin D [25(OH)D] concentrations were measured in a cross-sectional sample of 270 T2DM patients aged over 50 y from Zhejiang. Data on demographic characteristics, anthropometry and other variables were collected. The mean of serum 25(OH)D was 22.93 ng/mL, and percentages of vitamin D deficiency and insufficiency were 43.71% and 39.63%, respectively. Serum 25(OH)D concentrations were significantly lower in subjects with MetS than in those without MetS (21.74 vs 24.96 ng/mL, p=0.001), and the prevalence of MetS significantly increased according to tertiles of serum 25(OH)D concentrations. After adjusting for multivariate factors, the adverse effect of lower serum 25(OH)D concentrations was significant (OR: 3.26, 95% CI: 1.03-7.34; p=0.044) in the group with BMI≥24 kg/m2 while the change in OR of MetS for each 10 ng/mL decrease in the serum 25(OH)D concentrations was 2.03 (95% CI: 1.10-3.79). These results suggest that serum 25(OH)D deficiency may be a risk factor of MetS among Chinese type 2 diabetic patients, especially in the T2DM with BMI≥24 kg/m2. The challenge is determining the mechanisms of vitamin D action for recommendation of vitamin D supplementation that reduces the risks of MetS and progression to T2DM.

Vitamin D Deficiency Increases the Risk of Gestational Diabetes Mellitus: A Meta-Analysis of Observational Studies.

The results investigating the relationship between vitamin D levels and gestational diabetes mellitus (GDM) are inconsistent. Thus, we focused on evaluating the association of vitamin D deficiency with GDM by conducting a meta-analysis of observed studies. A systematic literature search was conducted via PubMed, MEDLINE, and Cochrane library to identify eligible studies before August 2015. The meta-analysis of 20 studies including 9209 participants showed that women with vitamin D deficiency experienced a significantly increased risk for developing GDM (odds ratio (OR) = 1.53; 95% confidence intervals (CI), 1.33, 1.75) with a little heterogeneity (I² = 16.20%, p = 0.252). A noteworthy decrease of 4.93 nmol/L (95% CI, -6.73, -3.14) in serum 25(OH)D was demonstrated in the participants with GDM, and moderate heterogeneity was observed (I² = 61.40%, p = 0.001). Subgroup analysis with study design showed that there were obvious heterogeneities in nested case-control studies (I² > 52.5%, p < 0.07). Sensitivity analysis showed that exclusion of any single study did not materially alter the overall combined effect. In summary, the evidence from this meta-analysis indicates a consistent association between vitamin D deficiency and an increased risk of GDM. However, well-designed randomized controlled trials are needed to elicit the clear effect of vitamin D supplementation on prevention of GDM.