INS and diabetes mellitus: In a double-blind randomized clinical trial, weekly treatment with 50,000 IU oral vitamin D for eight weeks in vitamin D-deficient obese individuals with type 2 diabetes mellitus (T2DM) led to a significant decrease in HbA1c levels, but did not result in significant changes in fasting blood glucose (FBG), insulin, HOMA-IR index, or quantitative insulin sensitivity check index (QUICKI)17.