Body mass index cut-points to identify cardiometabolic risk in black South Africans
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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.
KeywordsBody mass index Black adults Cardiometabolic risk Sub-Saharan Africa
H.S.K. conceived the study and was responsible for quality control of anthropometric data and interpretation of the results. A.E.S. was responsible for quality control and interpretation of the blood pressure data. A.K. was involved in the study design and data collection of the PURE-North West data. C.M.W. was responsible for the study design and collection of the Free State data. K.L.R. advised on all statistical analyses and interpretation of the results. All authors were involved in writing the paper and final approval of the submitted version. Dr. Suria Ellis of the Statistical Consultation Service at North-West University performed the sample weighting analysis. The authors would like to thank all supporting staff and the participants of the PURE and AHA-FS studies and in particular: PURE-South Africa: The PURE-NWP-SA research team, field workers and office staff in the Africa Unit for Transdisciplinary Health Research (AUTHeR), Faculty of Health Sciences, North-West University, Potchefstroom, South Africa. PURE International: Dr. S. Yusuf and the PURE project office staff at the Population Health Research Institute (PHRI), Hamilton Health Sciences and McMaster University, Ontario, Canada.
The study received funding from South African Medical Research Council, South Africa-Netherlands Research Programme on Alternatives in Development, South African National Research Foundation (North-West and Free State studies), North-West University and Population Health Research Institute, Canada. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors, and therefore, the National Research Foundation does not accept any liability in regard thereto.
Compliance with ethical standards
Conflict of interest
The authors declare no conflict of interest.
The North West and Free State studies were approved by the Ethics Committees of the North-West University and the University of the Free State. Research has been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. Volunteers gave written informed consent prior to their inclusion in the study.
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