Vitamin D3 deficiency is associated with more severe insulin resistance and metformin use in patients with type 2 diabetes

Background: Vitamin D3 (vit. D3) deficiency is considered as one of the main factors involved in the development of type 2 diabetes (T2D). We assessed insulin resistance (IR), ?-cell functional activity and metabolic profile according to 25(OH) vit. D3 status in patients with T2D. Methods: The study included 109 patients with T2D, divided in 3 groups: group 1 (N.=11) with normal levels of vit. D3 (>30 ng/mL); group 2 (N.=38) with vit. D3 insufficiency (21-29 ng/mL); and group 3 (N.=60) with vit. D3 deficiency (<20 ng/mL). IR and ?-cell functional activity were assessed as change in C-peptide concentration and homeostasis model assessment-estimated (HOMA) ?-cell function which was calculated using HOMA2 calculator. Results: Patients with vit. D3 deficiency presented significantly higher C-peptide concentration compared to other groups. HOMA2 (3.29±1.89 vs. 2.12±0.71; P=0.049) and hemoglobin (H8b)A1c (9.11±1.63 vs. 7.75±1.06; P=0.016) levels changed significantly only in patients with vit. D3 deficiency compared to diabetics with normal vit. D3 levels. Furthermore, in univariate Pearson's correlation analysis, we observed significant association between vit. D3 levels and C-peptide, insulin sensitivity, HOMA2, triglyceride-glucose index, HbA1c and Body Mass Index, only in the vit. D3 deficiency group. In multivariate logistic regression analysis, poor glycemic control, as defined by HbA1c levels, was independent from metformin use while high density lipoprotein-cholesterol levels were associated with vit. D3 deficiency. Conclusions: Our study demonstrated that vit. D3 deficiency in patients with T2D was associated with more severe IR, poor glycemic control and obesity compared to normal status or vit. D3 insufficiency.