Lack of effect of subtherapeutic vitamin D treatment on glycemic and lipid parameters in Type 2 diabetes: A pilot prospective randomized trial

BACKGROUND: Epidemiological studies suggest a higher prevalence of metabolic syndrome and its components among individuals with vitamin D deficiency. The aim of the present study was to determine whether vitamin D treatment improves glucose control and insulin sensitivity in Type 2 diabetes mellitus (T2DM). METHODS: Subjects with T2DM and serum 25-hydroxyvitamin D (25(OH)D) concentrations <25 ng/mL were randomized to receive 400 IU (Group 1) or 1200 IU (Group 2) cholecalciferol for 4 months. Fasting plasma glucose, glycosylated hemoglobin (HbA1c), Quantitative Insulin Sensitivity Check Index (QUICKI), serum lipid levels and serum adiponectin were measured at baseline and at 4 months. RESULTS: Mean 25(OH)D levels increased in both groups (from 17.6±1.5 to 25.5±1.8 ng/mL in Group 1 and from 15.6±1.4 to 27.4±2.4 ng/mL in Group 2; P≤0.001 vs baseline for each group). No significant differences were noted in fasting plasma glucose, HbA1c, QUICKI, serum adiponectin, and lipid levels compared with baseline within groups or between the two groups. CONCLUSIONS: In the present pilot study, conventional vitamin D treatment at a level improving, but not optimizing, serum 25(OH)D did not improve glycemia, insulin sensitivity, or lipid profile. However, diabetes and lipids were relatively well controlled at baseline. Future studies should be designed to achieve optimal concentrations of serum 25(OH)D (at least >32 ng/mL) and should include subjects showing more abnormal parameters of glycemia, lipid, and insulin sensitivity at baseline.