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Abstract
To evaluate the factors causing glucose intolerance in type 2 diabetes in Japan, insulin
secretion and insulin sensitivity were compared across the range of glucose tolerance.
Subjects were divided into 3 groups: normal glucose tolerance (NGT), impaired glucose
tolerance (IGT), and type 2 diabetes (DM) according to the criteria of the World Health
Organization (WHO). We examined insulin secretion and insulin sensitivity using fasting
blood glucose and insulin levels and 75 g oral glucose tolerance test (OGTT). We used
homeostasis model assessment (HOMA) beta-cell and insulinogenic index (30 minutes)
to estimate insulin secretion and HOMA-insulin resistance (IR) and insulin sensitivity
index (ISI) composite for insulin sensitivity. Although insulin resistance plays an
important role in the development of diabetes in many ethnic populations, the differences
in insulin sensitivity between NGT and IGT and between IGT and DM are small in Japanese
patients. On the other hand, as glucose intolerance increases, insulin secretion decreases
most remarkably both between NGT and IGT and between IGT and DM in Japanese patients.
Decreasing insulin secretion and decreasing insulin sensitivity both occur in developing
type 2 diabetes in Japanese patients, but decreased basal and early-phase insulin
secretion had more pronounced contribution to glucose tolerance than the indices of
insulin sensitivity. Japanese type 2 diabetic patients are characterized by a larger
decrease in insulin secretion and show less attribution of insulin resistance.