Variation in the Waist Circumference of Risk in Black Populations: A Comparison of African Immigrants and African-Americans

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SUN 758-779-Cardiometabolic Risk & Vascular Biology
Sunday, June 16, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SUN-774
Michelle Y O'Connor1, Madia Ricks1, Natalie LM Ramsey1, Amber B Courville2, Francine Thomas3, Peter T Katzmarzyk4, Jianhua Yao3 and Anne E Sumner*1
1NIDDK/NIH, Bethesda, MD, 2CC-NIH, Bethesda, MD, 3NIH, Bethesda, MD, 4Pennington Biomedical Research Center, Baton Rouge, LA
The adverse impact of central obesity is determined by the combined effects of insulin resistance and visceral adipose tissue (VAT). At best, data in Africans on the relationship of insulin resistance to either VAT or waist circumference (WC), a measure of central obesity, is sparse.  Furthermore it is unknown if there is variation in the WC of risk among different populations of African descent. Defining the “WC of risk” as the WC which best predicts insulin resistance, our goal was to compare in age-matched African-Americans (AA) and African immigrants the WC of risk and the relationship of WC to VAT. Data on 323 non-diabetics (48% African immigrants, 56% male, age 35±9y, mean±SD) were analyzed. Insulin resistance was defined by the lowest quartile of the insulin sensitivity index (SI<2.29). VAT was measured by a cross-sectional CT scan at L2-L3. Area under the receiver operating characteristic (AUC-ROC) curves and the Youden Index were used to identify the optimal WC. Overall, Africans lived in the United States for 11±9y. For Africans who immigrated as adults, self-reported weight gain in first 2 years after arrival was ~4 kg. BMI was lower in Africans than AA (Men: 27.0±3.7 vs. 29.6±6.2 kg/m2, P<0.01, Women: 27.0±5.6 vs. 31.6±8.6 kg/m2 , P<0.01). Adjusting for BMI, WC did not differ by ethnicity in men (93±6 vs. 93±6 cm, P=0.4) but was lower in African women than AA women (91±7 vs. 95±7 cm, P=0.01). VAT was higher in African than AA men (117±47cm2 vs. 86±47 cm2, P<0.01). Moreover, at every level of WC, VAT was 33 cm2 higher in African than AA men. In contrast, VAT did not differ between African and AA women (P=0.7), nor did the relationship of VAT to WC (P=0.7). The WC which best predicted insulin resistance in African and AA men were: 93 cm (AUC-ROC: 0.73) and 102 cm (AUC-ROC: 0.78) respectively. Equivalent WC in African and AA women were: 94 cm (AUC-ROC: 0.76) and 99 cm (AUC-ROC: 0.83), respectively. Hence, the WC which predicts insulin resistance is lower in Africans than AA. Rapid weight gain after arrival in the United States may account for greater insulin resistance at a lower WC, and for African immigrant men, more VAT at a lower WC. Overall, if major geographic transition occurs, the WC of risk may change over time and not be globally concordant across populations.

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