Insulin‐secretion capacity in normal glucose tolerance, impaired glucose tolerance, and diabetes in obese and non‐obese Japanese patients

Aims/Introduction: Pronounced reduction of insulin secretion in response to a rise in glucose level has been reported in Japanese patients compared with Caucasian patients, but the mean body mass index (BMI) is also lower in Japanese patients. As BMI is a determinant of insulin secretion, we examined insulin‐secretion capacity in obese and non‐obese Japanese patients. Materials and Methods: Using the oral glucose tolerance test (OGTT), we estimated the insulin‐secreting capacity in obese (BMI ≥ 25) and non‐obese (BMI < 25) Japanese patients, including 1848 patients with normal glucose tolerance (NGT), 321 patients with impaired glucose tolerance (IGT) and 69 diabetes (DM) patients. Results: The insulinogenic index (I.I.), calculated by dividing the increment in serum insulin by the increment in plasma glucose from 0 to 30 min during OGTT, decreased from NGT to IGT and to DM in patients with and without obesity. In patients with NGT, IGT and DM, the I.I. values of obese patients were higher than those of the non‐obese patients. The peak of insulin concentration in OGTT appeared at 60 min in NGT and at 120 min in IGT in both obese and non‐obese patients, but in DM it was observed at 120 min in obese patients and at 60 min in non‐obese patients. Conclusions: These results show that early‐phase insulin secretion in obese Japanese patients is higher than in non‐obese patients in all stages of glucose tolerance, and delayed insulin‐secretion capacity is also conserved in obese Japanese patients, even in IGT and DM, which is similar to Caucasian patients. (J Diabetes Invest, doi:10.1111/j.2040‐1124.2011.00180.x, 2011)