Ethnic differences in the ability of triglyceride levels to identify insulin resistance

Abstract

The Metabolic Syndrome is used to predict the onset of coronary artery disease and Type 2 diabetes. As the predictive value of the Metabolic Syndrome has been challenged, alternative syndromes have been developed. All of these syndromes were developed in populations that were predominantly non-Hispanic white (NHW). They include the Enlarged Waist Elevated Triglyceride Syndrome, the Overweight-Lipid Syndrome and the Hypertriglyceridemic Waist Syndrome. The first applies to postmenopausal women, the second to overweight individuals (BMI ≥ 25 kg/m 2), and the third to men. Each syndrome uses hypertriglyceridemia as a criterion. However, the definition of hypertriglyceridemia varies by syndrome i.e. TG ≥ 128 mg/dL for the Enlarged Waist Elevated Triglyceride Syndrome, TG ≥ 130 mg/dL for the Overweight-Lipid Syndrome, ≥150 mg/dL for the Metabolic Syndrome, and TG ≥ 176 mg/dL for the Hypertriglyceridemic Waist Syndrome. Insulin resistance and hypertriglyceridemia are highly correlated. But as insulin resistant non-Hispanic blacks (NHB) often have triglyceride (TG) levels below the thresholds set by these syndromes, the ability of either TG or these syndromes to identify high risk NHB is unknown. Using the National Health and Nutrition Examination Survey (NHANES) 1999–2002, our goals were to determine by ethnicity: (1) the prevalence of each of these syndromes; (2) the ability of fasting TG concentrations to identify insulin resistance at cut-off levels established by these syndromes, specifically 130, 150 and 176 mg/dL. Participants were 2804 adults from NHANES 1999–2002. The cohort was divided into tertiles of homeostasis model assessment. Insulin resistance was defined as the upper tertile (≥2.73). The prevalence of each syndrome was lower in NHB than NHW or Mexican Americans (MA) (all P < 0.05). Mean TG levels in NHB, non-Hispanic Whites (NHW) and Mexican Americans (MA) were: 99, 140 and 144 mg/dL, respectively. The mean percents of insulin-resistant NHB, NHW and MA with TG < 130 mg/dL were: 64, 31 and 36. The percents of insulin-resistant NHB, NHW and MA with TG < 150 mg/dL were: 75, 46 and 47. The percents of insulin-resistant NHB, NHW and MA with TG < 176 mg/dL were: 81, 58 and 59. Significance was P < 0.001 for each comparison to NHB. In conclusion, the prevalence of syndromes that use TG as a diagnostic criterion is lower in NHB than NHW or MA. NHB are more likely than NHW or MA to be insulin-resistant and have TG levels below threshold values. As syndromes are formulated to identify individuals at high risk for conditions such as cardiovascular disease and Type 2 diabetes, ethnic differences in TG levels should be considered.