Differences in Insulin Sensitivity and Secretory Capacity Based on OGTT in Subjects with Impaired Glucose Regulation

BACKGROUND: This study examined whether defects in insulin secretion contribute to the development and progression of type 2 diabetes mellitus (T2DM). METHODS: Plasma insulin and glucose were measured after a glucose tolerance test to calculate the insulinogenic index (IGI) and the HOMA-IR Homeostasis model assessment of insulin resistance in subjects with normal glucose tolerance (NGT), prediabetes (preDM, n=49), and T2DM patients with disease duration <1 year (n=84), 1~5 years (n=45), or >5 years (n=37). Plasma proinsulin and adiponectin levels were also measured as a parameter of insulin secretion and resistance. RESULTS: The mean HOMA-IR increased and the adiponectin levels decreased relative to the deterioration of glucose tolerance in NGT and preDM subjects. However, differences in the HOMA-IR were not related to disease duration in T2DM subjects. The mean IGI was similar in NGT and preDM subjects, but there were significant deteriorations in IGI relative to the duration of diabetes. CONCLUSIONS: Defects in both insulin sensitivity and insulin secretion contribute to T2DM, but decreased insulin secretion may be more important in the development and progression of T2DM.