The Changes in Early Phase Insulin Secretion in Newly Diagnosed, Drug Naive Korean Prediabetes Subjects

BACKGROUND There have been no systematic observations regarding changes in early phase insulin secretion among Korean prediabetes and early stage type 2 diabetes mellitus (T2DM) patients. METHODS We conducted 75-g oral glucose tolerance tests (OGTT) in 873 subjects with suspected abnormal glucose tolerance. All subjects were diagnosed as having normal glucose tolerance (NGT), prediabetes (preDM), or T2DM according to the OGTT results and the insulin secretory and insulin resistance indices of each subject were calculated. Additionally, we analyzed the changes in early phase insulin secretion according to changes in fasting (Glc(0)), post-prandial (Glc(120)) glucose and HbA1c (A1c) levels. RESULTS As compared to subjects with NGT, the insulin secretory indices of the preDM and T2DM subjects progressively declined, and the insulin resistance indices were progressively aggravated. Early phase insulin secretion decreased rapidly according to the increments of Glc(0), Glc(120) and A1c, and these changes were most prominent in the NGT stage. Compared to the control group, the early phase insulin secretion levels of the preDM or T2DM subjects were less than 50% when Glc(0) was over 100 mg/dL, Glc(120) was over 145 mg/dL, and A1c was over 5.8%. CONCLUSION This study suggests that progressive beta cell dysfunction in Koreans may be initiated and rapidly aggravated during the period generally designated as 'normal.'