Madia Ricks

Determining the Waist Circumference in African Americans Which Best Predicts Insulin Resistance

Total body size and central fat distribution are important determinants of insulin resistance. The BMI and waist circumference (WC) thresholds in African Americans that best predict insulin resistance are unknown. Our goal was to determine the BMI and WC values in African Americans, which optimally predict insulin resistance. The subjects were African Americans (68 men, 63 women), aged 35 ± 8 years (mean ± s.d.), with a BMI of 30.9 ± 7.5, in the range of 18.5–54.7 kg/m2, and with a WC of 98 ± 18, in the range of 69–173 cm. Insulin resistance was defined by the lowest tertile of the insulin sensitivity index (SI). The Youden index was calculated to determine the WC and BMI thresholds that predict insulin resistance with an optimal combination of sensitivity and specificity. In men the thresholds that optimally predicted insulin resistance were a BMI ≥30 kg/m2 or a WC ≥102 cm. For women, insulin resistance was best predicted by a BMI ≥32 kg/m2 or a WC ≥98 cm. In African Americans, insulin resistance (in men) was best predicted by a WC ≥102 cm, and in women by a WC ≥98 cm, or by a BMI value that fell in the obese category (men: ≥30 kg/m2, women: ≥32 kg/m2).

Metabolic Syndrome Does Not Detect Metabolic Risk in African Men Living in the U.S.

OBJECTIVE Metabolic risk and metabolic syndrome (MetSyn) prevalence were compared in Africans who immigrated to the U.S. and African Americans. If MetSyn were an effective predictor of cardiometabolic risk, then the group with a worse metabolic risk profile would have a higher rate of MetSyn. RESEARCH DESIGN AND METHODS Cross-sectional analyses were performed on 95 men (39 Africans, 56 African Americans, age 38 ± 6 years [mean ± SD]). Glucose tolerance was determined by oral glucose tolerance test, visceral adipose tissue (VAT) was determined by computerized tomography, and MetSyn was determined by the presence of three of five factors: central obesity, hypertriglyceridemia, low levels of HDL cholesterol, hypertension, and fasting hyperglycemia. RESULTS MetSyn prevalence was similar in Africans and African Americans (10 vs. 13%, P = 0.74), but hypertension, glycemia (fasting and 2-h glucose), and VAT were higher in Africans. CONCLUSIONS African immigrants have a worse metabolic profile than African Americans but a similar prevalence of MetSyn. Therefore, MetSyn may underpredict metabolic risk in Africans.

Effect of low-dose oral contraceptives on metabolic risk factors in African-American women.

CONTEXT The effect of oral contraceptive pill (OCP) use on cardiovascular risk in African-American women is unknown. OBJECTIVE Our objective was to examine in African-American women the effect of OCP use on insulin resistance, glucose intolerance, and triglycerides (TGs). DESIGN This was a cross-sectional study. SETTING The study was conducted at the National Institutes of Health Clinical Research Center. PARTICIPANTS A total of 104 healthy nondiabetic African-American women [21 OCP users, 83 controls, age mean +/- sd, 34.7 +/- 7.6 yr, body mass index (BMI) 31 +/- 8.4 kg/m(2)] was included in the study. INTERVENTIONS Subjects had oral glucose tolerance tests, insulin-modified frequently sampled iv glucose tolerance tests, and fasting lipid profiles. Insulin resistance was determined by the insulin sensitivity index (S(I)). MAIN OUTCOME MEASURES Insulin resistance, glucose tolerance status, and TG levels were determined. RESULTS Fasting glucose did not differ between OCP users and controls (P = 0.27). In contrast, compared with controls, 2-h glucose (135 +/- 23 vs.120 +/- 25 mg/dl; P = 0.01) and fasting TGs (73 +/- 31 vs.57 +/- 27 mg/dl; P = 0.02) were higher in OCP users. OCP users tended to be more insulin resistant than controls (S(I): 2.51 +/- 2.01 vs. 3.46 +/- 2.09; P = 0.09). Multiple regression analysis revealed that BMI, age, and OCP use were significant determinants of 2-h glucose (adjusted R(2) = 0.37; P < 0.001) and TG levels (adjusted R(2) = 0.21; P < 0.001). As BMI was a determinant of both 2-h glucose and TGs, participants were divided into nonobese and obese groups, and the analyses repeated. Among the nonobese women, the OCP users were more insulin resistant (S(I): 2.91 +/- 1.58 vs. 4.35 +/- 1.88; P = 0.03) and had a higher prevalence of glucose intolerance than controls (odds ratio 5.7; 95% confidence interval 1.4-24; P = 0.01). CONCLUSION In African-American women, OCP use is associated with an increase in markers of cardiovascular risk manifested by increased insulin resistance, glucose intolerance, and elevated TGs.

Evaluation of Quantitative Models of the Effect of Insulin on Lipolysis and Glucose Disposal

The effects of insulin on the suppression of lipolysis are neither fully understood nor quantified. We examined a variety of mathematical models analogous to the minimal model of glucose disposal (MMG) to quantify the combined influence of insulin on lipolysis and glucose disposal during an insulin-modified frequently sampled intravenous glucose tolerance test. The tested models, which include two previously published ones, consisted of separate compartments for plasma free fatty acids (FFA), glucose, and insulin. They differed in the number of compartments and in the action of insulin to suppress lipolysis that decreased the plasma FFA level. In one category of models, a single insulin compartment acted on both glucose and FFA simultaneously. In a second category, there were two insulin compartments, each acting on FFA and glucose independently. For each of these two categories, we tested 11 variations of how insulin suppressed lipolysis. We also tested a model with an additional glucose compartment that acted on FFA. These 23 models were fit to the plasma FFA and glucose concentrations of 102 subjects individually. Using Bayesian model comparison methods, we selected the model that best balanced fit and minimized model complexity. In the best model, insulin suppressed lipolysis via a Hill function through a remote compartment that acted on both glucose and FFA simultaneously, and glucose dynamics obeyed the classic MMG.

Worse Cardiometabolic Health in African Immigrant Men than African American Men: Reconsideration of the Healthy Immigrant Effect

BACKGROUND The healthy immigrant effect is a phrase that has been used for decades to describe better cardiometabolic health in African immigrants than African Americans. The recent global increase in cardiometabolic diseases raises the possibility that immigrant health may be changing. Therefore, a new assessment of cardiometabolic health in African immigrants is warranted. METHODS Glucose tolerance status, blood pressure, and visceral adipose tissue (VAT) volume were compared in 214 self-identified healthy men comprised of 138 African immigrants, 76 African Americans, mean age 36±9 years [mean±standard deviation (SD); range 20-64 years]. Insulin resistance was defined by the lowest quartile of the insulin sensitivity index (SI≤2.28 mU/L(-1)·min(-1)). The waist circumference (WC) which predicts insulin resistance was determined using receiver operating characteristic curves and the Youden index. RESULTS Body mass index (BMI) and WC were lower in African immigrants than African Americans (BMI, 27.4±3.8 vs. 29.3±5.5 kg/m(2), P<0.01; WC, 91±11 vs. 97±16 cm, P<0.01). However, blood pressure, fasting glucose, and 2-hr glucose were higher in the African immigrants (all P<0.01). In addition, African immigrants had a higher prevalence of previously undiagnosed diabetes (8% vs. 0%, P<0.01) and prediabetes (35% vs. 22%, P<0.01). After adjusting for WC, African immigrants had more visceral adipose tissue (VAT) than African Americans (P<0.01). Consequently, the WC that predicted insulin resistance was 92 cm in African immigrants but 102 cm in African Americans. CONCLUSION African immigrants were less obese than African Americans but had worse cardiometabolic health, specifically higher glucose levels, more hypertension, and greater visceral adiposity. Overall, the healthy immigrant effect may no longer be valid.

Higher acute insulin response to glucose may determine greater free fatty acid clearance in African-American women.

CONTEXT Obesity and diabetes are more common in African-Americans than whites. Because free fatty acids (FFA) participate in the development of these conditions, studying race differences in the regulation of FFA and glucose by insulin is essential. OBJECTIVE The objective of the study was to determine whether race differences exist in glucose and FFA response to insulin. DESIGN This was a cross-sectional study. SETTING The study was conducted at a clinical research center. PARTICIPANTS Thirty-four premenopausal women (17 African-Americans, 17 whites) matched for age [36 ± 10 yr (mean ± sd)] and body mass index (30.0 ± 6.7 kg/m²). INTERVENTIONS Insulin-modified frequently sampled iv glucose tolerance tests were performed with data analyzed by separate minimal models for glucose and FFA. MAIN OUTCOME MEASURES Glucose measures were insulin sensitivity index (S(I)) and acute insulin response to glucose (AIRg). FFA measures were FFA clearance rate (c(f)). RESULTS Body mass index was similar but fat mass was higher in African-Americans than whites (P < 0.01). Compared with whites, African-Americans had lower S(I) (3.71 ± 1.55 vs. 5.23 ± 2.74 [×10⁻⁴ min⁻¹/(microunits per milliliter)] (P = 0.05) and higher AIRg (642 ± 379 vs. 263 ± 206 mU/liter⁻¹ · min, P < 0.01). Adjusting for fat mass, African-Americans had higher FFA clearance, c(f) (0.13 ± 0.06 vs. 0.08 ± 0.05 min⁻¹, P < 0.01). After adjusting for AIRg, the race difference in c(f) was no longer present (P = 0.51). For all women, the relationship between c(f) and AIRg was significant (r = 0.64, P < 0.01), but the relationship between c(f) and S(I) was not (r = -0.07, P = 0.71). The same pattern persisted when the two groups were studied separately. CONCLUSION African-American women were more insulin resistant than white women, yet they had greater FFA clearance. Acutely higher insulin concentrations in African-American women accounted for higher FFA clearance.

Inconsistent Access to Food and Cardiometabolic Disease: The Effect of Food Insecurity

Food insecurity is defined as limited or uncertain ability to acquire nutritionally adequate and safe foods in socially acceptable ways. The United States Department of Agriculture (USDA) has divided food insecurity into two categories: low food security and very low food security. Low food security is characterized by irregular access to food, binge eating when food is available, overconsumption of energy-dense foods, obesity, and even type 2 diabetes. This type of food insecurity occurs in impoverished urban areas of high-income countries such as the United States. In contrast, very low food security is distinctly different from low food security and can lead to undernutrition and frank starvation. Very low food security is found in developing countries in both rural areas and urban slums. In these countries, food insecurity is often exacerbated by natural disasters and climate changes that compromise food availability. With a focus on the social, economic, and behavioral factors that promote obesity and cardiometabolic disease in food insecure households in the United States, this review will first define the key terms and concepts associated with food insecurity. Then, the characteristics of food insecure households and the relationship to cardiometabolic disease will be discussed. Finally, the cardiac consequences of food insecurity in developing countries will be briefly described.

Adiponectin and leptin in African Americans.

Objective: African Americans (AAs) have less visceral and more subcutaneous fat than whites, thus the relationship of adiponectin and leptin to body fat and insulin sensitivity in AA may be different from that in whites.

Detection of Abnormal Glucose Tolerance in Africans Is Improved by Combining A1C With Fasting Glucose: The Africans in America Study

OBJECTIVE Abnormal glucose tolerance is rising in sub-Saharan Africa. Hemoglobin A1c by itself and in combination with fasting plasma glucose (FPG) is used to diagnose abnormal glucose tolerance. The diagnostic ability of A1C in Africans with heterozygous variant hemoglobin, such as sickle cell trait or hemoglobin C trait, has not been rigorously evaluated. In U.S.-based Africans, we determined by hemoglobin status the sensitivities of 1) FPG ≥5.6 mmol/L, 2) A1C ≥ 5.7% (39 mmol/mol), and 3) FPG combined with A1C (FPG ≥5.6 mmol/L and/or A1C ≥5.7% [39 mmol/mol]) for the detection of abnormal glucose tolerance. RESEARCH DESIGN AND METHODS An oral glucose tolerance test (OGTT) was performed in 216 African immigrants (68% male, age 37 ± 10 years [mean ± SD], range 20–64 years). Abnormal glucose tolerance was defined as 2-h glucose ≥7.8 mmol/L. RESULTS Variant hemoglobin was identified in 21% (46 of 216). Abnormal glucose tolerance occurred in 33% (72 of 216). When determining abnormal glucose tolerance from the OGTT (2-h glucose ≥7.8 mmol/L), sensitivities of FPG for the total, normal, and variant hemoglobin groups were 32%, 32%, and 33%, respectively. Sensitivities for A1C were 53%, 54%, and 47%. For FPG and A1C combined, sensitivities were 64%, 63%, and 67%. Sensitivities for FPG and A1C and the combination did not vary by hemoglobin status (all P > 0.6). For the entire cohort, sensitivity was higher for A1C than FPG and for both tests combined than for either test alone (all P values ≤ 0.01). CONCLUSIONS No significant difference in sensitivity of A1C by variant hemoglobin status was detected. For the diagnosis of abnormal glucose tolerance in Africans, the sensitivity of A1C combined with FPG is significantly superior to either test alone.

A1C Combined With Glycated Albumin Improves Detection of Prediabetes in Africans: The Africans in America Study.

OBJECTIVE Slowing the diabetes epidemic in Africa requires improved detection of prediabetes. A1C, a form of glycated hemoglobin A, is recommended for diagnosing prediabetes. The glycated proteins, fructosamine and glycated albumin (GA), are hemoglobin-independent alternatives to A1C, but their efficacy in Africans is unknown. Our goals were to determine the ability of A1C, fructosamine, and GA to detect prediabetes in U.S.-based Africans and the value of combining A1C with either fructosamine or GA. RESEARCH DESIGN AND METHODS Oral glucose tolerance tests (OGTT) were performed in 217 self-identified healthy African immigrants (69% male, age 39 ± 10 years [mean ± SD], BMI 27.6 ± 4.5 kg/m2). A1C, fructosamine, and GA were measured. Prediabetes was diagnosed by American Diabetes Association criteria for glucose obtained from a 2-h OGTT. The thresholds to diagnose prediabetes by A1C, fructosamine, and GA were the cutoff at the upper tertile for each variable: ≥5.7% (39 mmol/mol) (range 4.2–6.6% [22.4–48.6 mmol/mol]), ≥230 µmol/L (range 161–269 µmol/L), and ≥13.35% (range 10.20–16.07%), respectively. RESULTS Prediabetes occurred in 34% (74 of 217). The diagnostic sensitivities of A1C, fructosamine, and GA were 50%, 41%, and 42%, respectively. The P values for comparison with A1C were both >0.3. Combining A1C with either fructosamine or GA increased sensitivities. However, the sensitivity of A1C combined with fructosamine was not better than for A1C alone (72% vs. 50%, P = 0.172). In contrast, the sensitivity of A1C combined with GA was higher than for A1C alone (78% vs. 50%, P < 0.001). CONCLUSIONS As individual tests, A1C, fructosamine, and GA detected ≤50% of Africans with prediabetes. However, combining A1C with GA made it possible to identify nearly 80% of Africans with prediabetes.