Waist circumference predicts clustering of cardiovascular risk factors in older South Africans

Objective and design. A cross-sectional analytical study to determine the cardiovascular risk factor profile of older residents of fishing villages on the West Coast of South Africa, and to determine which anthropometric measures are associated with risk factors. Subjects. A convenient community-based sample of 152 subjects of mixed ancestry aged 55 years and over was recruited door-to-door using an address list of age-eligible subjects provided by the local public health care clinics. Methods. Cardiovascular relationships were investigated between: (i) number of risk factors (hypertension, hypercholesterolaemia, diabetes) and body mass index (BMI), waist-to-hip ratio (WHR), and waist circumference; and (ii) continuous cardiovascular risk factor variables and physical activity, smoking, dietary intake, and 24-hour urinary sodium and potassium concentrations. Results. The prevalence of hypertension (≥160/95 mmHg) was 74.3% (95% CI: 67.2-81.4%). Neither 24-hour urinary sodium nor potassium concentrations was associated with blood pressure (BP). Past, but not present, moderate-intensity physical activity, particularly that associated with occupation, was negatively associated with systolic BP (r=-0.24, P<0.05). The prevalence of diabetes and hypercholesterolaemia (serum cholesterol ≤6.5 mmol/l) was 24.6% (95% CI: 17.2-32%) and 40% (95% CI: 31.8-48.2%), respectively. The percentage of subjects with 0, 1, or 2 or more cardiovascular risk factors was 13.4%, 44.1% and 42.5%, respectively. Subjects with a waist circumference ≥ 92 cm had a significantly higher number of cardiovascular risk factors than those with a waist circumference <92 cm (χ²=9.29, P<0.01), and this association remained significant even after controlling for age, sex and smoking (P < 0.05). Neither BMI tertiles according to sex, nor a BMI cut-point >30, was significantly associated with a clustering of risk factors. Conclusion. In a sample of older South Africans of mixed ancestry at high risk of cardiovascular disease, waist circumference ≥92 cm predicts clustering of risk factors, independently of BMI. This simple, population-specific reference value may provide a useful screening tool to identify at-risk individuals for targeted prevention for coronary heart disease and associated metabolic disorders.