Effect of Vitamin D Supplementation on Glucose Control and Inflammatory Response in Type II Diabetes: A Double Blind, Randomized Clinical Trial

Diabetes mellitus (DM) and vitamin D deficiency are major health concerns around the world. Evidence suggests a possible role of vitamin D in improvement of insulin secretion and sensitivity. We assessed whether vitamin D supplementation could be used in vitamin D deficient-type II diabetes to improve glucose metabolism, components of metabolic syndrome (MetS) and specific inflammatory biomarkers. A double blind, randomized clinical trial was conducted in King Khalid University Hospital, Saudi Arabia to evaluate the effect of cholecalciferol supplementation on glycemic control, MetS components and specific inflammatory biomarkers including tumor necrosis factor-alpha (TNF-α), Interleukin (IL-6), leptin, adiponectin and vascular cell adhesion molecule-1 (VCAM-1). Twenty-two patients with type II diabetes with insulin resistance, glycated hemoglobin (HbA1c) ≥ 6 (42 mmol/mol) and serum 25(OH)D < 50 nmol/L were randomized using a computer program to receive either supplementation with cholecalciferol (5000 IU/day) or placebo for 12 weeks. The primary outcome was change in HbA1c levels from baseline. Median [IQR] 25(OH)D levels increased significantly in the vitamin D group as 58.1 [48, 67.3] nmol/L (P = 0.002). There was no significant difference in the change of HbA1c between the groups (P = 0.5) with a decrease of -0.1% [-1, 0.5] in the vitamin D group and an increase of 0.15% [0.1, 0.2] in the placebo group. A significant improvement was observed in the homeostasis model of assessment of β-cell activity (HOMA-%B) (P = 0.03) with vitamin D supplementation compared to baseline. Vitamin D repletion for 12 weeks increased serum vitamin D concentrations and improved β-cell activity in vitamin D-deficient type II diabetes with no significant changes in HbA1c or insulin sensitivity.