β-Cell Dysfunction Is Associated with Metabolic Syndrome Severity in Adults

Background: Metabolic syndrome is prevalent in adults characterized by increased visceral adiposity and insulin resistance (IR). However, the link between pancreatic beta-cell function and metabolic syndrome severity in adults across the glucose spectrum is unknown. We hypothesized that poor beta-cell function would independently predict a higher metabolic syndrome Z-score (i.e., severity). Methods: Seventy (12 normal glucose tolerant, 37 prediabetic, 21 type 2 diabetic) obese adults [62.4 +/- 1.1 year; 34.6 +/- 0.6 kg/m(2); data are mean +/- standard error of the mean (SEM)] participated in this cross-sectional study. A 2-hr 75-gram oral glucose tolerance test (OGTT) was administered, and insulin and glucose area under the curve was determined for calculations of insulin action. Fasting and glucose-stimulated insulin secretion was calculated using homeostasis model assessment of insulin secretion (HOMA-B) and the insulinogenic index (i.e., I0-30/Glc(0-30) or I60-120/Glc(60-120)), respectively. Fasting and postprandial insulin sensitivity was assessed by HOMA-IR and the Matsuda Index, respectively. beta-cell function was estimated using the disposition index via HOMA-B/HOMA-IR, I0-30/Glc(0-30) or I60-120/Glc(60-120)xMatsuda Index, which represents basal, first-, and second-phase insulin release, respectively. Body composition (via computerized tomography and dual X-ray absorptiometry) and sex-specific metabolic syndrome Z-scores were calculated from waist circumference, blood pressure, fasting glucose, triglycerides, and high-density lipoproteins. Results: Compared to those with normal glucose tolerance, visceral fat and IR were higher and beta-cell function was lower in adults with glucose intolerance and type 2 diabetes mellitus. Elevated visceral fat and IR (HOMA-IR and Matsuda Index) correlated with elevated Z-scores (r=0.51, r=0.54, r=-0.49; all P<0.002, respectively). Basal, first-, and second-phase beta-cell function correlated with low Z-scores (r=-0.59, r=-0.51, and r=-0.43, all P<0.001). Insulin secretion significantly predicted the Z-score independent of sex, body fat, blood lipids, blood pressure, IR, and glucose metabolism (P<0.005). Conclusion: beta-cell dysfunction is highly correlated with the severity of metabolic syndrome in adults. Future work is warranted to elucidate the mechanism by which cardiometabolic disturbances influence insulin secretion.