Body mass index cut-points to identify cardiometabolic risk in black South Africans

To determine optimal body mass index (BMI) cut-points for the identification of cardiometabolic risk in black South African adults.

We performed a cross-sectional study of a weighted sample of healthy black South Africans aged 25-65 years (721 men, 1386 women) from the North West and Free State Provinces. Demographic, lifestyle and anthropometric measures were taken, and blood pressure, fasting serum triglycerides, high-density lipoprotein (HDL) cholesterol and blood glucose were measured. We defined elevated cardiometabolic risk as having three or more risk factors according to international metabolic syndrome criteria. Receiver operating characteristic curves were applied to identify an optimal BMI cut-point for men and women.

BMI had good diagnostic performance to identify clustering of three or more risk factors, as well as individual risk factors: low HDL-cholesterol, elevated fasting glucose and triglycerides, with areas under the curve >.6, but not for high blood pressure. Optimal BMI cut-points averaged 22 kg/m² for men and 28 kg/m² for women, respectively, with better sensitivity in men (44.0-71.9 %), and in women (60.6-69.8 %), compared to a BMI of 30 kg/m² (17-19.1, 53-61.4 %, respectively). Men and women with a BMI >22 and >28 kg/m², respectively, had significantly increased probability of elevated cardiometabolic risk after adjustment for age, alcohol use and smoking.

In black South African men, a BMI cut-point of 22 kg/m² identifies those at cardiometabolic risk, whereas a BMI of 30 kg/m² underestimates risk. In women, a cut-point of 28 kg/m², approaching the WHO obesity cut-point, identifies those at risk.