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.

Glycated Albumin Identifies Prediabetes Not Detected by Hemoglobin A1c: The Africans in America Study.

BACKGROUND: Following immigration to the US, many Africans transition from a low-normal to a high-normal or overweight body mass index (BMI). This weight change is associated with a high rate of prediabetes in the nonobese. Studies in East Asians reveal that glycated albumin is effective in identifying prediabetes in nonobese Asians. Whether this is true in African immigrants is unknown. Therefore, we evaluated the ability of hemoglobin A1c (Hb A1c) and glycated albumin to detect prediabetes in nonobese (BMI <30 kg/m2) and obese (BMI ≥30 kg/m2) African immigrants. METHODS: Oral glucose tolerance tests (OGTTs) were performed in 236 self-identified healthy African immigrants [mean (SD) BMI 27.6 (4.4) kg/m2]. Prediabetes diagnosis was based on glucose criteria for the OGTT. Diagnostic sensitivity of Hb A1c and glycated albumin was determined by thresholds at the upper quartile for each [Hb A1c ≥5.7% (39 mmol/mol), glycated albumin ≥13.77%]. RESULTS: Based on glucose criteria for the OGTT, prediabetes was detected in 36% (85/236). BMI and Hb A1c were positively correlated (r = 0.22, P < 0.001), whereas BMI and glycated albumin were negatively correlated (r = -0.24, P < 0.001). Although the sensitivities of Hb A1c and glycated albumin were similar in nonobese immigrants (37% vs 42%, P = 0.75), prediabetes was detected in 21 nonobese Africans by glycated albumin alone, in 18 by Hb A1c alone, and in 4 by both tests. Therefore, sensitivity of the combined tests was better than for Hb A1c alone(72% vs 37%, P < 0.01). In the obese, Hb A1c was a much better diagnostic test than glycated albumin (64% vs 16%, P < 0.01) and combining the tests did not improve sensitivity (72% vs 64%, P = 0.50). CONCLUSIONS: Glycated albumin contributes by identifying prediabetes not detected by Hb A1c in nonobese African immigrants. ClinicalTrials.gov Identifier: NCT00001853.

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/m(2)). 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.

Age at Immigration and Kidney Function among Self-Identified Healthy Africans in the United States.

Kidney disease disparately affects those of African descent. Age trends have generally been established for kidney function in the overall US population, but the contribution of age at the time of immigration for African immigrants is unknown. To examine the independent and joint effects of age and age at the time of immigration, and kidney function. Estimated glomerular filtration rate (eGFR) was calculated for 93 African immigrants (60 % male; mean age = 33.5). Hierarchical regression and post hoc analyses revealed a significant age × age at the time of immigration interaction after accounting for traditional risk factors among those who immigrated at age ≤21. Younger age at the time of immigration to the US may exacerbate an inverse relationship between age and kidney function in a self-identified healthy African immigrant sample. Investigation of biopsychosocial factors associated with kidney health among African immigrants is warranted.

Sickle Cell Trait from a Metabolic, Renal, and Vascular Perspective: Linking History, Knowledge, and Health.

Sickle cell trait (SCT) is at the intersection of genetics, social policy, and medicine. SCT occurs in three-hundred million people worldwide and in approximately 8 % of African-Americans. There has been great debate about the influence of SCT on health. Yet data exist, albeit controversial, which suggest that SCT is associated with metabolic derangements that can lead to sudden death after vigorous physical activity, renal dysfunction, thromboembolic events, and stroke. In addition, it has even been postulated that SCT might enhance the vascular complications of diabetes. This review focuses on (a) the scientific breakthroughs that led to the discovery of hemoglobin S, sickle cell disease, and SCT, (b) the history of screening programs in the United States, (c) the incidence and etiology of exercise-related sudden death in military personnel and athletes with SCT, and (d) the data examining the potential chronic disease consequences of SCT from a metabolic, renal, and vascular perspective.

Biochemical and clinical deficiency is uncommon in African immigrants despite a high prevalence of low vitamin D: the Africans in America study.

UNLABELLED: African ancestry is associated with low vitamin D levels but high bone density. Fifty percent of African immigrants had low vitamin D levels, but <10 % had evidence of deficiency. The value of providing vitamin D supplementation to African immigrants without evidence of deficiency needs to be determined. INTRODUCTION: The Endocrine Society and Institute of Medicine (IOM) have concluded from studies in largely white populations that 25(OH)D is necessary for bone health. However, their definition of vitamin D insufficiency differs. The Endocrine Society recommends a 25(OH)D threshold of <30 ng/mL. The IOM uses a lower threshold of 25(OH)D of <20 ng/mL. As African ancestry is associated with decreased 25(OH)D but increased bone mineral density (BMD), the applicability of these thresholds to Africans is unknown. Therefore, we examined in African immigrants the relationship of 25(OH)D to parathyroid hormone (PTH) and BMD. METHODS: One hundred eighty-six African immigrants(69 % male, age 38 ± 10 (mean ± SD), range 20-64 years) living in metropolitan Washington, DC, were enrolled. BMD was determined from whole-body dual-energy X-ray absorptiometry (DXA) scans. Decreased BMD required T-scores ≤-1.0. The threshold for low 25(OH)D was the concentration of 25(OH)D at which PTH became suppressed. This is known as the inflection point. Biochemical deficiency required low 25(OH)D and PTH of >65 pg/mL. Clinical deficiency required low 25(OH)D and T-scores ≤-1.0. RESULTS: 25(OH)D <30 and <20 ng/mL occurred in 83 and 46 % of African immigrants, respectively. PTH inversely correlated with 25(OH)D (r = -0.31, P = 0.002). The inflection point occurred at a 25(OH)D concentration of 20 ng/mL. Biochemical and clinical deficiency occurred in only 8 and 3 % of immigrants, respectively. CONCLUSION: As PTH became suppressed at 25(OH)D of 20 ng/mL, the 25(OH)D <20 ng/mL threshold for insufficiency may apply to African immigrants. However, ~50 % of African immigrants have 25(OH)D <20 ng/mL, but only <10 % had evidence of deficiency. The value of providing vitamin D supplementation to the large number of African immigrants with 25(OH)D <20 ng/mL and no detectable evidence of deficiency needs to be determined.

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.

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.

Racial differences between African-American and white women in insulin resistance and visceral adiposity are associated with differences in apoCIII containing apoAI and apoB lipoproteins.

BACKGROUND: African-Americans have higher HDL, less visceral adipose tissue (VAT) and lower triglyceride (TG) and apoCIII concentrations than whites, despite being more insulin-resistant. We studied in African-American and white women the influences of insulin resistance and VAT on the apoAI concentrations of two HDL subspecies, one that contains apoCIII that is associated with increased risk of coronary heart disease (CHD) and one that does not have apoCIII that is associated with decreased CHD; and on the apoCIII concentrations of HDL and of the apoB lipoproteins. METHODS: The participants were 32 women (14 African-Americans, 18 white) of similar age (39 ± 12 vs. 42 ± 11y). Mean BMI was 34 kg/m(2) in the African-Americans compared to 30 in the whites. A standard diet (33% fat, 52% carbohydrate, 15% protein) was provided for 7 days followed by a test meal (40% fat, 40% carbohydrate, 20% protein) on Day 8. Insulin sensitivity index (SI) was calculated from the minimal model. RESULTS: After controlling for SI, African-Americans have a higher mean apoAI level in HDL with apoCIII compared with whites (12.9 ± 2.8 and 10.9 ± 2.9 mg/dL, respectively, P = 0.05). SI was associated with higher apoAI in HDL with apoCIII, whereas VAT was not associated with this HDL subspecies. This pattern of results was reversed for apoCIII concentrations in apoB lipoproteins. After adjusting for SI, African-Americans had lower apoCIII in apoB lipoproteins. SI was associated with lower apoCIII in total apoB lipoproteins, whereas VAT was associated with higher apoCIII in all the apoB lipoproteins. Additional adjustment for VAT tended to reduce the difference in apoCIII between the groups. CONCLUSIONS: African-American women have a higher HDL with apoCIII level than whites when controlled for insulin sensitivity. African-Americans have lower insulin sensitivity. Insulin sensitivity is associated with higher levels of HDL with apoCIII. ApoCIII levels in VLDL are lower in African-American women than whites, also affected by insulin sensitivity which is associated with low apoCIII in VLDL. VAT has a strong association with apoCIII in apoB lipoproteins but not with apoAI in HDL with apoCIII. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT00484861.

ApoC-III and visceral adipose tissue contribute to paradoxically normal triglyceride levels in insulin-resistant African-American women.

BACKGROUND: African-Americans are more insulin-resistant than whites but have lower triglyceride (TG) concentrations. The metabolic basis for this is unknown. Our goal was to determine in a cross-sectional study the effect of insulin resistance, visceral adipose tissue (VAT) and the apolipoproteins, B, C-III and E, on race differences in TG content of very low density lipoproteins (VLDL). METHODS: The participants were 31 women (16 African-American, 15 white) of similar age (37 ± 9 vs. 38 ± 11y (mean ± SD), P = 0.72) and BMI (32.4 ± 7.2 vs. 29.3 ± 6.0 kg/m2, P = 0.21). A standard diet (33% fat, 52% carbohydrate, 15% protein) was given for 7 days followed by a test meal (40% fat, 40% carbohydrate, 20% protein) on Day 8. Insulin sensitivity index (SI) was calculated from the minimal model. VAT was measured at L2-3. The influence of race, SI, VAT and apolipoproteins on the TG content of VLDL was determined by random effects models (REM). RESULTS: African-Americans were more insulin-resistant (SI: 3.6 ± 1.3 vs. 5.6 ± 2.6 mU/L-1.min-1, P < 0.01) with less VAT (75 ± 59 vs. 102 ± 71 cm2, P < 0.01). TG, apoB and apoC-III content of light and dense VLDL were lower in African-Americans (all P < 0.05 except for apoC-III in light VLDL, P = 0.11). ApoE content did not vary by race. In REM, VAT but not SI influenced the TG concentration of VLDL. In models with race, SI, VAT and all apolipoproteins entered, race was not significant but apoC-III and VAT remained significant determinants of TG concentration in light and dense VLDL. CONCLUSIONS: Low concentrations of apoC-III and VAT in African-Americans contribute to race differences in TG concentrations. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT00484861.

The uncertain significance of low vitamin D levels in African descent populations: a review of the bone and cardiometabolic literature.

Vitamin D levels in people of African descent are often described as inadequate or deficient. Whether low vitamin D levels in people of African descent lead to compromised bone or cardiometabolic health is unknown. Clarity on this issue is essential because if clinically significant vitamin D deficiency is present, vitamin D supplementation is necessary. However, if vitamin D is metabolically sufficient, vitamin D supplementation could be wasteful of scarce resources and even harmful. In this review vitamin D physiology is described with a focus on issues specific to populations of African descent such as the influence of melanin on endogenous vitamin D production and lactose intolerance on the willingness of people to ingest vitamin D fortified foods. Then data on the relationship of vitamin D to bone and cardiometabolic health in people of African descent are evaluated.

Triglyceride-based screening tests fail to recognize cardiometabolic disease in African immigrant and African-American men.

BACKGROUND: The prevalence of cardiometabolic disease in Africa now rivals that of Western nations. Therefore, screening programs that lead to effective prevention of cardiometabolic disease in Africans is imperative. Most screening tests for cardiometabolic disease use triglyceride (TG) levels as a criterion. However, the failure rate of TG-based screening tests in African Americans is high. In Africans, the efficacy of TG-based screening tests is unknown. Our goal was to determine the association between hypertriglyceridemia (TG ≥150 mg/dL) and cardiometabolic disease in African and African-American men. RESEARCH DESIGN AND METHODS: This was a cross-sectional study of 155 men (80 African immigrants, 75 African Americans) [age, 35±9 years, mean±standard deviation (SD), body mass index (BMI) 28.5±5.2 kg/m(2)] who self-identified as healthy. Lipid profiles were performed. Glucose tolerance and insulin resistance was determined by oral glucose tolerance tests (OGTT) and the insulin sensitivity index (S(I)), respectively. Cardiometabolic disease was defined by four possible subtypes--prediabetes, diabetes, insulin resistance, or metabolic triad [hyperinsulinemia, hyperapolipoprotein B, small low-density lipoprotein (LDL) particles]. RESULTS: TG levels were higher in men with cardiometabolic disease than without (88±43 versus 61±26 mg/dL, P<0.01). However, <10% of men with cardiometabolic disease had TG ≥150 mg/dL. Even within each cardiometabolic disease subtype, the prevalence of TG ≥150 mg/dL was <10%. Furthermore, TG levels in the 5% of men identified by OGTT as diabetic were ≤100 mg/dL (mean 71±24, range 45-100 mg/dL). CONCLUSIONS: Hypertriglyceridemia is a poor marker of cardiometabolic disease in men of African descent. Therefore TG-based screening tests fail to identify both African immigrants and African-American men with cardiometabolic disease. As a consequence, the opportunity for early intervention and prevention is lost.

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.

Postprandial endothelial function does not differ in women by race: an insulin resistance paradox?

Insulin resistance is associated with endothelial dysfunction. Because African-American women are more insulin-resistant than white women, it is assumed that African-American women have impaired endothelial function. However, racial differences in postprandial endothelial function have not been examined. In this study, we test the hypothesis that African-American women have impaired postprandial endothelial function compared with white women. Postprandial endothelial function following a breakfast (20% protein, 40% fat, and 40% carbohydrate) was evaluated in 36 (18 African-American women, 18 white women) age- and body mass index (BMI)-matched (age: 37 ± 11 yr; BMI: 30 ± 6 kg/m(2)) women. Endothelial function, defined by percent change in brachial artery flow-mediated dilation (FMD), was measured at 0, 2, 4, and 6 h following a meal. There were no significant differences between the groups in baseline FMD, total body fat, abdominal visceral fat, and fasting levels of glucose, insulin, total cholesterol, low-density lipoprotein cholesterol, or serum estradiol. Although African-American women were less insulin-sensitive [insulin sensitivity index (mean ± SD): 3.6 ± 1.5 vs. 5.2 ± 2.6, P = 0.02], both fasting triglyceride (TG: 56 ± 37 vs. 97 ± 49 mg/dl, P = 0.007) and incremental TG area under the curve (AUC(0-6hr): 279 ± 190 vs. 492 ± 255 mg·dl(-1)·min(-1)·10(-2), P = 0.008) were lower in African-American than white women. Breakfast was associated with a significant increase in FMD in whites and African-Americans, and there was no significant difference in postprandial FMD between the groups (P > 0.1 for group × time interactions). Despite being insulin-resistant, postprandial endothelial function in African-American women was comparable to white women. These results imply that insulin sensitivity may not be an important determinant of racial differences in endothelial function.

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.

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.

Waist circumference, BMI, and visceral adipose tissue in white women and women of African descent.

Although waist circumference (WC) is a marker of visceral adipose tissue (VAT), WC cut-points are based on BMI category. We compared WC-BMI and WC-VAT relationships in blacks and whites. Combining data from five studies, BMI and WC were measured in 1,409 premenopausal women (148 white South Africans, 607 African-Americans, 186 black South Africans, 445 West Africans, 23 black Africans living in United States). In three of five studies, participants had VAT measured by computerized tomography (n = 456). Compared to whites, blacks had higher BMI (29.6 ± 7.6 (mean ± s.d.) vs. 27.6 ± 6.6 kg/m², P = 0.001), similar WC (92 ± 16 vs. 90 ± 15 cm, P = 0.27) and lower VAT (64 ± 42 vs. 101 ± 59 cm², P < 0.001). The WC-BMI relationship did not differ by race (blacks: ß (s.e.) WC = 0.42 (.01), whites: ß (s.e.) WC = 0.40 (0.01), P = 0.73). The WC-VAT relationship was different in blacks and whites (blacks: ß (s.e.) WC = 1.38 (0.11), whites: ß (s.e.) WC = 3.18 (0.21), P < 0.001). Whites had a greater increase in VAT per unit increase in WC. WC-BMI and WC-VAT relationships did not differ among black populations. As WC-BMI relationship did not differ by race, the same BMI-based WC guidelines may be appropriate for black and white women. However, if WC is defined by VAT, race-specific WC thresholds are required.

The TG/HDL-C ratio does not predict insulin resistance in overweight women of African descent: a study of South African, African American and West African women.

Women of African descent have a high prevalence of diseases caused by insulin resistance. To positively impact cardiometabolic health in Black women, effective screening tests for insulin resistance must be identified. Recently, the TG/HDL-C ratio has been recommended as a tool to predict insulin resistance in overweight people. While the ratio predicts insulin resistance in White women, it is ineffective in African American women. As there are no data for African women, we tested the ability of the TG/HDL-C ratio to predict insulin resistance in Black women from South Africa, West Africa and the United States. For comparison, the ratio was also tested in White women from South Africa. Participants were 801 women (157 Black South African, 382 African American, 119 West African, 143 White South African, age 36 +/- 9y [mean +/- SD]). Standardized scores were created from log-transformed homeostasis model assessment-insulin resistance values from each population. Participants in the upper third of their population distribution were classified as insulin-resistant. To predict insulin resistance by the TC/HDL-C ratio, area under the receiver operating characteristic (AUC-ROC) curve was used and criteria were: 0.50 for no discrimination and > or = 0.70 for acceptable. Seventy-one percent of the Black women were overweight vs 51% of White women (P<.01). In overweight White women, AUC-ROC curve for prediction of insulin resistance by TG/HDL-C was 0.76 +/- 0.06, but below the 0.70 threshold in each group of overweight Black women (Black South African: 0.64 +/- 0.06, African American: 0.66 +/- 0.03, and West African: 0.63 +/- 0.07). Therefore, TG/HDL-C does not predict insulin resistance in overweight African American women and this investigation extends that finding to overweight Black South African and West African women. Resources to identify effective markers of insulin resistance are needed to improve cardiometabolic health in women of African descent.

Validity of the reduced-sample insulin modified frequently-sampled intravenous glucose tolerance test using the nonlinear regression approach.

The disposition index, the product of the insulin sensitivity index (S(I)) and the acute insulin response to glucose, is linked in African Americans to chromosome 11q. This link was determined with S(I) calculated with the nonlinear regression approach to the minimal model and data from the reduced-sample insulin-modified frequently-sampled intravenous glucose tolerance test (Reduced-Sample-IM-FSIGT). However, the application of the nonlinear regression approach to calculate S(I) using data from the Reduced-Sample-IM-FSIGT has been challenged as being not only inaccurate but also having a high failure rate in insulin-resistant subjects. Our goal was to determine the accuracy and failure rate of the Reduced-Sample-IM-FSIGT using the nonlinear regression approach to the minimal model. With S(I) from the Full-Sample-IM-FSIGT considered the standard and using the nonlinear regression approach to the minimal model, we compared the agreement between S(I) from the Full- and Reduced-Sample-IM-FSIGT protocols. One hundred African Americans (body mass index, 31.3 +/- 7.6 kg/m(2) [mean +/- SD]; range, 19.0-56.9 kg/m(2)) had FSIGTs. Glucose (0.3 g/kg) was given at baseline. Insulin was infused from 20 to 25 minutes (total insulin dose, 0.02 U/kg). For the Full-Sample-IM-FSIGT, S(I) was calculated based on the glucose and insulin samples taken at -1, 1, 2, 3, 4, 5, 6, 7, 8,10, 12, 14, 16, 19, 22, 23, 24, 25, 27, 30, 40, 50, 60, 70, 80, 90, 100, 120, 150, and 180 minutes. For the Reduced-Sample-FSIGT, S(I) was calculated based on the time points that appear in bold. Agreement was determined by Spearman correlation, concordance, and the Bland-Altman method. In addition, for both protocols, the population was divided into tertiles of S(I). Insulin resistance was defined by the lowest tertile of S(I) from the Full-Sample-IM-FSIGT. The distribution of subjects across tertiles was compared by rank order and kappa statistic. We found that the rate of failure of resolution of S(I) by the Reduced-Sample-IM-FSIGT was 3% (3/100). For the remaining 97 subjects, S(I) for the Full- and Reduced-Sample-IM-FSIGTs were as follows: 3.76 +/- 2.41 L mU(-1) min(-1) (range, 0.58-14.50) and 4.29 +/- 2.89 L mU(-1) min(-1) (range, 0.52-14.42); relative error, 21% +/- 18%; Spearman r = 0.97; and concordance, 0.94 (both P < .001). After log transformation, the Bland-Altman limits of agreement were -0.29 and 0.53. The exact agreement for distribution of the population in the insulin-resistant tertile vs the insulin-sensitive tertiles was 92%, kappa of 0.82 +/- 0.06. Using the nonlinear regression approach and data from the Reduced-Sample-IM-FSIGT in subjects with a wide range of insulin sensitivity, failure to resolve S(I) occurred in only 3% of subjects. The agreement and maintenance of rank order of S(I) between protocols support the use of the nonlinear regression approach to the minimal model and the Reduced-Sample-IM-FSIGT in clinical studies.