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

BACKGROUND: To 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. METHODS: The 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. RESULTS: Women 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. CONCLUSION: Working 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.

Stress Measured by Allostatic Load Score Varies by Reason for Immigration: The Africans in America Study.

OBJECTIVE: Reason for immigration as a biological stress has not been studied in Africans. Our goal was to determine in African immigrants, if biological stress measured by allostatic load score (ALS) varies by reason for immigration. METHODS: Using an ALS which had been previously developed with the National Health and Nutrition Examination Survey (NHANES) data to assess stress due to racism and nativity, ALS was calculated in 85 African immigrants (67% male, age 42 ± 10 years). For confirmation, we tested five additional ALS also built from NHANES. RESULTS: The two reasons for immigration which consistently had the lowest ALS were family reunification and lottery winner for self and immediate family. The other reasons for immigration such as study, asylum/refugee, and work had higher ALS. As reasons for immigration with the lowest ALS promoted family unity, they were combined (group 1) and the Africans who came for other reasons were combined (group 2). ALS in group 1 vs. group 2 was 1.96 ± 1.40 vs. 2.94 ± 1.87, P = 0.03. CONCLUSIONS: Biological stress varies by reason for immigration and appears to be mitigated by maintaining family unity. Overall, reason for immigration is an important biographical data likely to influence health.

Time to glucose peak during an oral glucose tolerance test identifies prediabetes risk.

CONTEXT: Morphological characteristics of the glucose curve during an oral glucose tolerance test (OGTT) (time to peak and shape) may reflect different phenotypes of insulin secretion and action, but their ability to predict diabetes risk is uncertain. OBJECTIVE: To compare the ability of time to glucose peak and curve shape to detect prediabetes and ß-cell function. DESIGN AND PARTICIPANTS: In a cross-sectional evaluation using an OGTT, 145 adults without diabetes (age 42±9 years (mean±SD), range 24-62 years, BMI 29.2±5.3 kg/m2 , range 19.9-45.2 kg/m2 ) were characterized by peak (30 minutes vs >30 minutes) and shape (biphasic vs monophasic). MAIN OUTCOME MEASURES: Prediabetes and disposition index (DI)-a marker of ß-cell function. RESULTS: Prediabetes was diagnosed in 36% (52/145) of participants. Peak>30 minutes, not monophasic curve, was associated with increased odds of prediabetes (OR: 4.0 vs 1.1; P<.001). Both monophasic curve and peak>30 minutes were associated with lower DI (P≤.01). Time to glucose peak and glucose area under the curves (AUC) were independent predictors of DI (adjR2 =0.45, P<.001). CONCLUSION: Glucose peak >30 minutes was a stronger independent indicator of prediabetes and ß-cell function than the monophasic curve. Time to glucose peak may be an important tool that could enhance prediabetes risk stratification.

The Association between Stress Measured by Allostatic Load Score and Physiologic Dysregulation in African Immigrants: The Africans in America Study.

INTRODUCTION: Allostatic load score (ALS) summarizes the physiological effect of stress on cardiovascular, metabolic and immune systems. As immigration is stressful, ALS could be affected. OBJECTIVE: Associations between age of immigration, reason for immigration, and unhealthy assimilation behavior and ALS were determined in 238 African immigrants to the United States (age 40 ± 10, mean ± SD, range 21-64 years). METHODS: ALS was calculated using 10 variables from three domains; cardiovascular (SBP, DBP, cholesterol, triglyceride, homocysteine), metabolic [BMI, A1C, albumin, estimated glomerular filtration rate (eGFR)], and immunological [high-sensitivity C-reactive protein (hsCRP)]. Variables were divided into sex-specific quartiles with high-risk defined by the highest quartile for each variable except for albumin and eGFR, which used the lowest quartile. One point was assigned if the variable was in the high-risk range and 0 if not. Unhealthy assimilation behavior was defined by a higher prevalence of smoking, alcohol consumption, or sedentary activity in immigrants who lived in the US for ≥10 years compare to <10 years. RESULTS: Sixteen percent of the immigrants arrived in the US as children (age < 18 years); 84% arrived as adults (age ≥ 18 years). Compared to adulthood immigrants, childhood immigrants were younger (30 ± 7 vs. 42 ± 9, P < 0.01) but had lived in the US longer (20 ± 8 vs. 12 ± 9 years, P < 0.01). Age-adjusted ALS was similar in childhood and adulthood immigrants (2.78 ± 1.83 vs. 2.73 ± 1.69, P = 0.87). For adulthood immigrants, multiple regression analysis (adj R2 = 0.20) revealed older age at immigration and more years in the US were associated with higher ALS (both P < 0.05); whereas, current age, education, income, and gender had no significant influence (all P ≥ 0.4). The prevalence of smoking, alcohol intake, and physical activity did not differ in adulthood immigrants living in the US for ≥10 years vs. <10 years (all P ≥ 0.2). Reason for immigration was available for 77 participants. The reasons included: family reunification, lottery, marriage, work, education, and asylum. Compared to all other reasons combined, immigration for family reunification was associated with the lowest ALS (1.94 ± 1.51 vs. 3.03 ± 1.86, P = 0.03). CONCLUSION: African immigrants do not appear to respond to the stress of immigration by developing unhealthy assimilation behaviors. However, older age at immigration and increased duration of stay in the US are associated with higher ALS; whereas, family reunification is associated with lower ALS. CLINICAL TRIALSGOV IDENTIFIER: NCT00001853.