Do current guidelines for waist circumference apply to black Africans? Prediction of insulin resistance by waist circumference among Africans living in America

Abstract

BackgroundTo lower the risk of diabetes and heart disease in Africa, identification of African-centred thresholds for inexpensive biomarkers of insulin resistance (IR) is essential. The waist circumference (WC) thresholds that predicts IR in African men and women have not been established, but investigations recently conducted in Africa using indirect measures of IR suggest IR is predicted by WC of 80–95 cm in men and 90–99 cm in women. These WC cannot be used for guidelines until validated by direct measurements of IR and visceral adipose tissue (VAT). Therefore, we determined in a group of African-born black people living in America (A) the WC, which predicts IR and (B) the influence of abdominal fat distribution on IR.MethodsThe 375 participants (age 38±10 years (mean±SD), 67% men) had IR determined by HOMA-IR and Matsuda index. VAT and subcutaneous adipose tissue (SAT) were measured by abdominal CT scans. Optimal WC for the prediction of IR was determined in sex-specific analyses by area under the receiver operating characteristic (AUC-ROC) and Youden index.ResultsWomen had more SAT (203±114 vs 128±74 cm2) and less VAT than men (63±48 vs 117±72 cm2, p<0.001). Optimal WC for prediction of IR in men and women were: 91 cm (AUC-ROC: 0.80±0.03 (mean±SE)) and 96 cm (AUC-ROC: 0.81±0.08), respectively. Regression analyses revealed a significant sex–VAT interaction (p<0.001). Therefore, for every unit increase in VAT, women had a 0.94 higher unit increase in SAT and 0.07 higher unit increase in WC than men.ConclusionWorking with a group of African-born black people living in America, we accessed technology, which validated observations made in Africa. Higher SAT at every level of VAT explained why the WC that predicted IR was higher in women (96 cm) than men (91 cm). For Africans to benefit from WC measurements, convening a panel of experts to develop evidence-based African-centred WC guidelines may be the way forward.

Metabolic characteristics of Africans with normal glucose tolerance and elevated 1-hour glucose: insight from the Africans in America study

“…Conversely, beta-cell failure in the absence of obesity is a rising concern in low- and middle-income countries. In an earlier analysis of the Africans in America cohort, we found that beta-cell failure without insulin resistance occurred in 40% of African-born blacks with abnormal glucose tolerance 21. Yet studies in African-born blacks living in America are not sufficient for understanding the African experience with diabetes.…”

“…Reasons for beta-cell failure in low- and middle-income countries of Africa are complex but include both genetic and environmental factors such as early life undernutrition 21 39–42. We speculate that data from 1-hour glucose during an OGTT could become an epidemiological tool used to determine the extent of beta-cell dysfunction in African countries.…”

“…The Africans in America cohort was established to assess risk for diabetes and heart disease in African-born blacks living in the USA 20 21. Recruitment was by newspaper advertisements (45%), participant referrals (30%), presentations at community events, flyers and electronic outreach.…”

“…Participants fasted for 12 hours and came to the Clinical Center at 7:00. Weight, height, blood pressure and waist circumference (WC) were obtained 21. A blood sample was obtained for glycated hemoglobin measurement and hemoglobin electrophoresis.…”

“…After OGTT-1 was completed, a CT scan (Siemens and Somatom Force Scanner, Munich, Germany) was performed for measurement of visceral adipose tissue at vertebrae L2–3 using automated software 21…”