Discordance between insulin resistance and metabolic syndrome: features and associated cardiovascular risk in adults with normal glucose regulation

Abstract

The aims of this study were to investigate the extent of concordance between metabolic syndrome (MS) and insulin resistance (IR), the features of discordance, and the magnitude of their independent association with cardiovascular disease (CVD) risk. After exclusion of individuals with diabetes and impaired fasting glucose, the population sample of 1534 men and women, representative of Turkish adults (mean age, 52.2 years), were evaluated cross-sectionally and at a mean 2 years' follow-up. Metabolic syndrome was identified by criteria of the Adult Treatment Panel III, except for male waist circumference (>94 cm). Insulin resistance was defined by the upper quartile in the sample (>2.245) of the homeostatic model assessment (HOMA) index. Clinical fatal and nonfatal CVD existed or developed in 165 subjects. Waist circumference proved to be by far the strongest significant determinant of HOMA in both sexes, followed by triglycerides. The cohort was categorized into 4 by the presence or absence of MS and IR. Each of the latter represented 34% and 25%, but together constituted 45% of the sample, thus disclosing concordance in a third of the conditions combined. The nonconcordant IR/NoMS group was less common than the MS/NoIR group and was distinct from the latter in having significantly lower waist girth, blood pressure, apolipoprotein B and triglyceride levels, and higher high-density lipoprotein cholesterol, glucose, and insulin levels and physical activity in both sexes. When adjusted for 5 important risk factors, although the excess risk in men with MS failed to attain significance, men with IR were associated with a significant 1.9-fold CVD risk. The IR/NoMS group had a 2.2-fold (95% confidence interval, 0.97-5.11) CVD likelihood compared with the large insulin-sensitive group, after adjustment for age, sex, log C-reactive protein, low-density lipoprotein cholesterol, smoking status, physical activity, and the 2 groups of MS with or without IR. Overlapping between MS and IR is limited in either sex, and MS/NoIR is more common than IR/NoMS. Overall, IR is more significantly associated with CVD risk than MS in men and in both sexes after adjustment for important confounders. Insulin resistance without MS tends to implicate in middle-aged and elderly Turkish men roughly a 2-fold CVD risk, corresponding to 50% excess risk per 1 SD in HOMA index, independent of MS and important covariates.