Insulin secretory capacity and insulin sensitivity in impaired fasting glucose in Japanese.

Aims/Introduction:  Impaired fasting glucose (IFG) increases the risk of developing diabetes mellitus (DM). This study was carried out to characterize Japanese patients who have fasting glucose levels (FPG) between 100 and 109 mg/dL (IFG100–109). Materials and Methods:  A total of 1383 Japanese participants were examined by oral glucose tolerance test. We compared insulin secretory capacity (insulinogenic index) and insulin sensitivity (ISI composite) of IFG100–109/normal glucose tolerance (NGT; 100 ≤ FPG < 110 mg/dL and 2-h postchallenge glucose level (2-hPG) < 140 mg/dL) with NGT (100 mg/dL < FPG and 2-hPG < 140 mg/dL) and IFG110–125/NGT (110 ≤ FPG < 126 mg/dL and 2-hPG < 140 mg/dL). In addition, IFG100–109 patients were analyzed in three subgroups according to glucose intolerance by 2-hPG. Results:  Of the three categories of IFG100–109, IFG100–109/DM had the lowest insulinogenic index despite an ISI composite showing only a small decline from IFG100–109/NGT through IFG100–109/IGT (100 ≤ FPG < 110 mg/dL and 140 ≤ 2-hPG < 200 mg/dL) to IFG100–109/DM (100 ≤ FPG < 110 mg/dL and 200 mg/dL < 2-hPG). By multiple regression analysis, the insulinogenic index showed a significant relationship with 2-h PG levels. Both insulinogenic index and ISI composite were decreased significantly from NGT through IFG100–109/NGT to IFG110–125/NGT. Conclusions:  Although impaired early-phase insulin secretion plays the more important role in the elevation of postchallenge glucose in IFG100–109 patients, both impaired early-phase insulin secretion and decreased insulin sensitivity are involved in the deterioration of FPG in Japanese. In addition, insulin secretory defect and decreased insulin sensitivity already have begun in patients with IFG100–109.(J Diabetes Invest, doi: 10.1111/j.2040-1124.2012.00201.x, 2012)