Objective: Metabolic syndrome (MetS) defines cardiovascular disease (CVD) risks. Despite higher rates of obesity, type 2 diabetes, and hypertension, African Americans have lower rates of MetS when compared to Caucasians, which is paradoxical, since African Americans are more insulin resistant and have higher rates of cardiovascular morbidity and mortality when compared to White Americans. We hypothesized that genetic inheritance predisposes African Americans to the greater cardiovascular risk and the associated morbidity and mortality. Therefore, we investigated the prevalence of components of MetS in obese, glucose-tolerant, first degree relatives of African American patients with type 2 diabetes.
Methods: We examined the clinical and metabolic characteristics of 201 first-degree relatives (159 females and 42 males, mean age 41 +/- 8 years, and mean body mass index (BMI) of 32 +/- 8 (kg/m2). The subjects were categorized with MetS according to the Adult Treatment Panel (ATP) III criteria. Insulin sensitivity (Bergman minimal model method) and insulin resistance (homeostasis model assessment [HOMA]) were determined. We compared the clinical and metabolic characteristics in the relatives with and without MetS. Where appropriate, we compared the prevalence of the components of MetS in our African American sample with those of African American data in the National Health and Nutrition Evaluation Survey (NHANES) III.
Results: Comparing the MetS group (n=65) vs control subjects (n=136), the mean age, BMI, and percent body fat were greater in the MetS group. Mean fasting serum glucose, insulin and C-peptide levels were also greater in the MetS group. Insulin resistance index (HOMA-IR) was higher in the MetS group (HOMA-IR: 3.7 +/- 2.7 vs 2.2 +/- 1.7, P=.0002). Mean insulin sensitivity tended to be lower in the MetS group (2.16 +/- 2.64 vs 2.82 +/- 2.31, P=.08). In addition, despite the moderately severe insulin resistance, the MetS group had very low serum triglyceride levels and was the parameter least likely to meet the ATP criteria. The metabolic cutoff points for ATP III criteria were much lower in African American first-degree relatives with MetS. Of the five components of the ATP III criteria, waist circumference was the single most common parameter to likely meet the MetS criteria. We found that the prevalence of MetS was 29% in women and 40% in men when compared with 20.9% in African American women and 13.9% for African American men in the NHANES III.
Conclusion: We found that: 1) the prevalence of MetS is higher in a subgroup of African Americans who were first-degree relatives of patients with type 2 diabetes than that of African Americans in the NHANES III; and 2) waist circumference rather than metabolic parameters was the single most important parameter and was more likely to meet the MetS criteria in African American relatives.