Changes in Insulin Sensitivity and Insulin Release in Relation to Glycemia and Glucose Tolerance in 6414 Finnish Men

Abstract

Objective. We evaluated insulin sensitivity and insulin secretion across the entire range of fasting (FPG) and 2-hour plasma glucose (2hPG), and investigated the differences in insulin sensitivity and insulin release in different glucose tolerance categories.

Research Design and Methods. A total of 6414 Finnish men (age 57±7 years, BMI 27.0±3.9 kg/m²) from our ongoing population-based METSIM Study were included. Of them 2168 subjects had normal glucose tolerance (NGT), 2859 isolated impaired fasting glucose (IIFG), 217 isolated impaired glucose tolerance (IIGT), 701 combination of IFG and IGT, and 469 newly diagnosed type 2 diabetes.

Results. Matsuda index of insulin sensitivity decreased substantially within the normal range of FPG (−17%) and 2hPG (−37%), and was ∼−65 and ∼−53% in the diabetic range of FPG and 2hPG, compared to the reference range (FPG and 2hPG <5.0mmo/l). The early-phase insulin release declined only by ∼−5% within the normal range of FPG and 2hPG, but decreased significantly in the diabetic range of FPG (by 32-70%) and 2hPG (by 33-51%). Changes in insulin sensitivity and insulin secretion in relation to hyperglycemia were independent of obesity. The predominant feature of IIGT was impaired peripheral insulin sensitivity. IIFG was characterised by impaired early and total insulin release.

Conclusions. Peripheral insulin sensitivity decreased substantially already at low plasma glucose levels within the normoglycemic range, whereas the impairment in insulin secretion was observed mainly in the diabetic range of FPG and 2hPG. Obesity did not affect changes in insulin sensitivity or insulin secretion in relation to hyperglycemia.