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

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 NGTFPG1, NGTFPG2 and NGTFPG3, or by body mass index (BMI) tertile, ≤21.8, 21.9-24.4 and ≥24.5 kg/m2, into NGTBMI1, NGTBMI2 and NGTBMI3. 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 NGTFPG3, NGTFPG2 and NGTBMI3, but not in NGTFPG1, NGTBMI2 and NGTBMI1. 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.