Hyperbolic correlation between insulin sensitivity and insulin secretion fades away in lean subjects with superb...

The relationship between insulin sensitivity (Si) and insulin secretion (β) was analyzed in 533 health examinees. The subjects underwent a 75 g oral glucose tolerance test, with plasma glucose (PG) and immunoreactive insulin (IRI) determined at fasting, 30 min and 120 min, and were classified according to the current criteria as normal glucose tolerance (NGT, n=328), non-diabetic hyperglycemia (NDH, n=113) including impaired fasting glucose and impaired glucose tolerance, and diabetes mellitus (DM, n=72). NGT was subdivided by fasting PG (FPG) tertile, ≤4.9, 5.0-5.4 and 5.5-6.0 mM, into NGT(FPG1), NGT(FPG2) and NGT(FPG3), or by body mass index (BMI) tertile, ≤21.8, 21.9-24.4 and ≥24.5 kg/m², into NGT(BMI1), NGT(BMI2) and NGT(BMI3). As an index of Si and β, Matsuda index=10,000/sqrt[FPG·FIRI·2hPG·2hIRI] and δIRI₀₋₃₀/δPG₀₋₃₀, were employed respectively: FIRI, 2hPG and 2hIRI denote fasting IRI, 2h-post glucose PG and IRI, respectively. Correlation between Si and β was evaluated by Spearman's rank correlation and the parameters for [β]=a·[Si](b) were obtained by standardized major axis (SMA) regression. Si-β correlation was strongest in NDH (Spearman's rho=-0.546, SMA regression r²=0.277), intermediate in DM (rho=-0.432, r²=0.193) and weakest in NGT (rho=-0.201, r²=0.039). Spearman's rho for the Si-β correlation was significantly lower in NGT than in NDH (p=0.003). Si-β correlation was significant in NGT(FPG3), NGT(FPG2) and NGT(BMI3), but not in NGT(FPG1), NGT(BMI2) and NGT(BMI1). The slope, b, was -1.184˜-1.530 without significant differences between any groups. In conclusion, the hyperbolic Si-β correlation was weaker in NGT than in NDH and absent in NGT subjects belonging to the lowest FPG or BMI tertile.