Increased insulin resistance and insulin secretion in nondiabetic African-Americans and Hispanics compared with non-Hispanic whites. The Insulin Resistance Atherosclerosis Study

Body composition and metabolic factors in obese children and adolescents

OBJECTIVE

Body composition is associated with metablic factors in adults; however, data are limited regarding obese children. This study was undertaken to assess body composition, regional fat distribution, and metabolic factors in obese 6-18-y-old children and adolescents.

DESIGN

Cross-sectional assessment.

SUBJECTS

Thirty-six obese children and adolescents, (mean+/-s.e.m.) age 11.8+/-0.5 y, BMI 34.1+/-1.2 kg/m(2).

MEASUREMENTS

Body composition was assessed by dual energy X-ray absorptiometry and computerized tomography. Fasting insulin, glucose and leptin levels, and the homeostasis model assessment of insulin sensitivity (HOMA-IR) were assessed.

RESULTS

The girls had significantly lower glucose levels than the boys. The ethnic group differences (African American children vs white children) in fat mass, total CT fat, subcutaneous CT fat, insulin level, leptin level, and higher HOMA-IR were not significant after adjusting for age or pubertal stage. These differences in abdominal fat and subcutaneous abdominal fat were also not independent of total body fat or BMI. No ethnic group differences in visceral abdominal fat were noted. Insulin level and HOMA IR were associated with leptin level (independent of fat mass) and fat mass. Leptin level was associated with fat mass, total CT fat, and subcutaneous CT fat; however the associations between the CT fat measures and leptin were not independent of total body fat mass.

CONCLUSIONS

Neither visceral abdominal fat, subcutaneous abdominal fat, insulin levels, or insulin resistance differed by ethnic group when adjusted for age or pubertal status. This contrasts with findings in adults and non-obese children which suggest lower levels of visceral fat and higher insulin levels and insulin resistance in African American children and adolescents.

Metabolic response to a mixed meal in obese and lean women from two South african populations

OBJECTIVE

Lower lipid and insulin levels are found during a glucose-tolerance test in obese black than obese white South African women. Therefore, beta-cell function and lipid metabolism were compared in these populations during a mixed meal.

RESEARCH METHODS AND PROCEDURES

Blood concentrations of glucose, free fatty acids (FFAs), insulin, lipograms, and in vivo FFA oxidation were determined at fasting and for 7 hours after oral administration of a mixed emulsion containing glucose-casein-sucrose-lipid and [1-(13)C] palmitic acid in 8 lean black women (LBW), 10 obese black women (OBW), 9 lean white women (LWW), and 10 obese white women (OWW). Subcutaneous and visceral fat mass was assessed by computerized tomography.

RESULTS

Visceral fat area was higher in OWW (152.7 +/- 17.0 cm(2)) than OBW (80.0 +/- 6.7 cm(2); p < 0.01). In OBW, 30-minute insulin levels were higher (604.3 +/- 117.6 pM) than OWW (311.0 +/- 42.9 pM; p < 0.05). Total triglyceride was higher in OWW (706.7 +/- 96.0 mM x 7 hours) than OBW (465.7 +/- 48.2 mM x 7 hours; p < 0.05) and correlated with visceral fat area (beta = 0.38, p = 0.05). Palmitate oxidation was higher in lean than obese women in both ethnic groups and correlated negatively with fat mass (beta = -0.58, p < 0.005).

DISCUSSION

The higher 30-minute insulin response in OBW may reflect a higher insulinotropic effect of FFAs or glucose. The elevated triglyceride level of OWW may be due to their higher visceral fat mass and possibly reduced clearance by adipose tissue.

Effects of weight loss on changes in insulin sensitivity and lipid concentrations in premenopausal African American and white women

BACKGROUND

Few studies have tested the hypothesis that changes in disease risk factors are more closely associated with changes in visceral fat than with changes in other adipose tissue depots, particularly in subjects with different ethnic or racial backgrounds.

OBJECTIVE

We describe changes in triacylglycerol, total cholesterol, HDL cholesterol, LDL cholesterol, insulin sensitivity (S(i)), visceral fat, and subcutaneous abdominal adipose tissue (SAAT) with weight loss in premenopausal, overweight [body mass index (in kg/m(2)): 27-30], African American (n = 19) and white (n = 18) women.

DESIGN

Assessments were performed before and after diet-induced weight loss to a BMI < 25. Body composition and body fat distribution were assessed with dual-energy X-ray absorptiometry and computed tomography, respectively; S(i) was assessed with an intravenous-glucose-tolerance test and minimal modeling.

RESULTS

White women lost significantly more visceral fat and less SAAT than did African American women despite similar weight losses (approximately 13 kg). Mixed-model analysis indicated significant effects of time (ie, weight loss) on S(i), triacylglycerol, HDL cholesterol, and LDL cholesterol and of race on triacylglycerol. Time x race interaction terms were not significant. After adjustment for either total body or visceral fat, time was not related to any outcome variable; however, race remained significantly related to triacylglycerol.

CONCLUSIONS

With weight loss, moderately overweight African American and white women experienced significant improvements in S(i) and lipids. The beneficial effects of weight loss did not differ with race and could not be attributed to a specific body fat depot. Lower triacylglycerol concentrations among African American women are independent of both obesity status and body fat distribution.

Hyperinsulinemia in african-american children: decreased insulin clearance and increased insulin secretion and its relationship to insulin sensitivity

African-American (AA) children are hyperinsulinemic and insulin resistant compared with American White (AW) children. This study investigated 1) whether AA/AW differences in insulinemia are associated with differences in insulin clearance; 2) whether dietary patterns, mainly carbohydrate and fat intake, play a role; and 3) whether the quantitative relationship between insulin sensitivity and secretion is similar between AA and AW children. Forty-four prepubertal children (22 AA and 22 AW) with comparable body composition and visceral adiposity were studied. All underwent a 3-h hyperinsulinemic (40 mU x m(-2) x min(-1))-euglycemic clamp to calculate insulin sensitivity and insulin clearance and a 2-h hyperglycemic clamp (12.5 mmol/l) to assess first- and second-phase insulin responses. Twenty-four-hour food recalls were analyzed for macronutrient intake. Insulin clearance (19.5 +/- 0.7 vs. 22.9 +/- 1.1 ml x min(-1) x kg(-1) fat-free mass [FFM]; P = 0.011) and insulin sensitivity were lower in AA versus AW children (14.8 +/- 1.0 vs. 18.9 +/- 1.4 micro mol x min(-1) x kg(-1) FFM; P = 0.021). Both insulin clearance and insulin sensitivity correlated inversely with dietary fat/carbohydrate ratio, which was higher in AA than in white children. Fasting C-peptide and insulin were higher in AA children with no difference in proinsulin levels. First- and second-phase insulin concentrations and glucose disposition index (insulin sensitivity x first-phase insulin) were higher in AA than in white children (12.8 +/- 2.1 vs. 7.2 +/- 0.6 micro mol. min(-1) x kg(-1) FFM; P = 0.019). In conclusion, the hyperinsulinemia observed in AA children is due to both lower insulin clearance and higher insulin secretion compared with their white peers. The quantitative relationship between insulin secretion and sensitivity is upregulated in AA children. This suggests that increased insulin secretion in AA children is not merely a compensatory response to lower insulin sensitivity. Dietary factors may have a role. Additional studies are needed to determine whether metabolic/nutritional factors, possibly mediated through free fatty acids, may play a role in the hyperinsulinism observed in AA children.

Serum insulin, obesity, and the incidence of type 2 diabetes in black and white adults: the atherosclerosis risk in communities study: 1987-1998

OBJECTIVE

In this study, we tested the hypothesis that fasting serum insulin is higher in nonobese black adults than in white adults and that high fasting insulin predicts type 2 diabetes equally well in both groups.

RESEARCH DESIGN AND METHODS

At the baseline examination (1987-1989) of the Atherosclerosis Risk in Communities Study, fasting insulin and BMI were measured in 13,416 black and white men and women without diabetes. Participants were examined at years 3, 6, and 9 for incident diabetes based on fasting glucose and American Diabetes Association criteria.

RESULTS

Fasting insulin was 19.7 pmol/l higher among nonobese (BMI <30 kg/m(2)) black women compared with white women (race and obesity interaction term, P < 0.01). There were no differences among men. Among nonobese women, the relative risk for developing diabetes was similar between racial groups: 1.4 (95% CI 1.2-1.5) and 1.3 (1.2-1.4) per 60 pmol/l increase in insulin (P < 0.01) for black and white women, respectively (interaction term, P = 0.6). Findings were similar among men. Adjusting for established risk factors did not attenuate this association.

CONCLUSIONS

Nonobese black women have higher fasting insulin levels than nonobese white women, and fasting insulin is an equally strong predictor of diabetes in both groups. These results suggest one mechanism to explain the excess incidence of diabetes in nonobese black women but do not explain the excess among black men. Future research should evaluate additional factors: genetic, environmental, or the combination of both, which might explain higher fasting insulin among black women when compared with white women.

Heterogeneity in the relationship between ethnicity, BMI, and fasting insulin

OBJECTIVE

To determine whether the association of BMI and fasting insulin is modified by ethnicity.

RESEARCH DESIGN AND METHODS

Non-Hispanic black (black), non-Hispanic white (white), and Mexican-American men and women aged 20-80 years from the Third National Health and Nutrition Examination Survey (1988-1994) were included in this study. Linear regression models with an interaction term were used to test whether ethnicity modified the association between BMI and fasting insulin.

RESULTS

Fasting insulin was 19, 26, 20, and 19% higher in black women than white women with BMI levels of <22, 22-24, 25-27, and 28-30 kg/m(2), respectively. These differences between black and white women converged at BMI levels >30 kg/m(2). Mexican-American women had fasting insulin levels that were 17, 22, 20, and 16% higher than those of white women at BMI levels of 25-27, 28-30, 31-33, and >34 kg/m(2), respectively, but were not different in individuals with BMI levels <25 kg/m(2). Adjusting for established risk factors did not attenuate these associations in women. Differences in fasting insulin among men were not as apparent.

CONCLUSIONS

These findings suggest that the effect of obesity on insulin sensitivity is different for Americans in ethnic minorities. In black subjects, fasting insulin is higher at lean weight when compared with white and Mexican-American subjects. In Mexican-American subjects, fasting insulin is higher in overweight individuals when compared with white and black subjects. These findings are more pronounced in women than in men. This result reinforces the importance of designing prevention programs that are tailored to meet the needs of specific populations. Investigation of possible explanations for these differences seems warranted.

Use of somatostatin receptor ligands in obesity and diabetic complications

Somatostatin (SMS) is a potent inhibitory molecule. It inhibits both exocrine and endocrine secretory functions of the pancreas, suppresses growth hormone secretion and reduces the level of insulin-like growth factor-1. Long-acting somatostatin analogues were currently investigated for potential clinical benefits in two settings: (a) control of hyperinsulinaemia in obesity and (b) control of an excess of pro-angiogenic factors in diabetes-associated retinal complications. In two randomized, controlled trials the long-acting somatostatin analogue octreotide retarded progression of the microvascular complications in pre-proliferative and advanced stages of diabetic retinopathy. Inhibition of the early phase of insulin secretion by use of octreotide in patients with hypothalamic obesity resulted in weight loss and improved quality of life. Efficacy of octreotide correlated to residual beta-cell activity prior to the treatment. Obesity and diabetes mellitus are the most common chronic metabolic disorders in the world. The use of somatostatin analogues addressing the various hormonal imbalances of these disorders may provide a novel concept for their pharmacological treatment.

Contribution of insulin secretion and clearance to glucose-induced insulin concentration in african-american and caucasian children

Relative to Caucasians (C), African-American (AA) children and adults have lower indices of insulin sensitivity (S(i)) and a higher acute insulin response to glucose (AIR(g)). Among AA children, AIR(g) is greater than that which would be predicted based on lower S(i). The objectives of the present study were 1) to determine whether insulin secretory parameters differ in AA vs. C children and adolescents using C-peptide modeling, 2) to determine whether hepatic insulin extraction differs with ethnicity/race using the C-peptide to insulin molar ratio, and 3) to determine whether the relatively greater AIR(g) among African-Americans is due to greater insulin secretion or lesser clearance. Subjects (n = 76) were AA and C children (mean age, approximately 11 yr). A 3-h tolbutamide-modified iv glucose tolerance test and minimal modeling were used to determine S(i) and AIR(g). First phase C-peptide/insulin secretion and basal, first, and second phase beta-cell sensitivity to glucose were determined using C-peptide modeling with standard kinetic parameters developed in adults. The incremental C-peptide to insulin molar ratio over the 3-h test period, an index of hepatic insulin extraction, was calculated with the trapezoidal method. S(i) was lower and AIR(g) was higher in AA vs. C children. First phase C-peptide/insulin secretion and first phase beta-cell sensitivity to glucose were approximately 2-fold greater in AA vs. C children (P < 0.001); there were no between-group differences in basal or second phase beta-cell sensitivity to glucose. Hepatic insulin extraction was lower in AA vs. C (3.77 +/- 1.78% vs. 5.99 +/- 2.18%; P < 0.001). Multiple linear regression modeling indicated that first phase C-peptide/insulin secretion and hepatic insulin extraction contributed independently to AIR(g); however, it was only first phase C-peptide/insulin secretion that explained the significant independent contribution of ethnicity/race to AIR(g) after adjusting for S(i). The results of this study suggest that greater AIR(g) among AA is due to both greater insulin secretion and lesser hepatic insulin extraction, and that AIR(g) above that predicted based on lower S(i) is due to greater insulin secretion. The insulin secretion data await verification that the kinetic parameters used apply to children and AA.

Racial differences in insulin resistance and mid-thigh fat deposition in postmenopausal women

OBJECTIVE

To determine whether racial differences in insulin resistance between African American (AA) and white women exist in postmenopausal women and whether they are related to physical fitness and/or obesity.

RESEARCH METHODS AND PROCEDURES

We studied 35 obese AA (n = 9) and white (n = 26) women of comparable maximal oxygen consumption, obesity, and age. Total body fat was measured by DXA. Abdominal and mid-thigh low-density lean tissue (a marker of intramuscular fat) were determined with computed tomography. Glucose utilization (M) was measured during the last 30 minutes of a 3-hour hyperinsulinemic-euglycemic clamp. Insulin sensitivity was estimated from the relationship of M to the concentration of insulin during the last 30 minutes of the clamp.

RESULTS

The percentage of fat and total body fat mass were similar between AA and white women, whereas fat-free mass was higher in African American women. Visceral adipose tissue was not different between groups, but subcutaneous abdominal fat was 17% higher in the AA than in the white women. AA women had an 18% greater mid-thigh muscle area (p < 0.01) and a 34% greater mid-thigh low-density lean tissue area than the white women. Fasting glucose concentrations were not different, but fasting insulin concentrations were 29% higher in AA women. Glucose utilization was 60% lower in the AA women because of a lower non-oxidative glucose disposal. Insulin sensitivity was 46% lower in the AA women.

DISCUSSION

AA postmenopausal women have more mid-thigh intramuscular fat, lower glucose utilization, and are less insulin sensitive than white women despite comparable fitness and relative body fat levels.

Diabetes, diversity, and disparity: what do we do with the evidence?

The US Department of Health and Human Services has developed an initiative called "Eliminating Racial and Ethnic Disparities in Health," which parallels Healthy People 2010, the nation's health goals for the next decade. The initiative focuses on areas of health disparity that are known to affect racially and ethnically diverse groups of the population yet hold the promise of improvement. The first step to addressing such health inequities is to understand the scope and nature of the diseases that contribute to such disparities. This commentary reviews the epidemiology and consequences of type 2 diabetes, particularly as it is manifested in socially and culturally diverse groups, and offers recommendations for actions to address the disparities resulting from diabetes.

Higher fasting insulin but lower fasting C-peptide levels in African Americans in the US population

BACKGROUND

Fasting serum insulin and fasting serum C-peptide are risk factors for developing type 2 diabetes. Because of the higher incidence of type 2 diabetes in African Americans and Hispanic Americans, it is likely that these groups may differ from non-Hispanic whites in their levels of insulin and C-peptide.

METHODS

We analyzed data from a nationally representative sample of adults in the US population for whom sociodemographic, clinical, and laboratory information were obtained. The data were used to describe distributions of fasting insulin and fasting C-peptide in non-Hispanic white, non-Hispanic black, and Mexican American men and women aged >or=20 years without a medical history of diabetes.

RESULTS

Among men, Mexican Americans had higher insulin values than non-Hispanic whites and blacks. Among women, both Mexican Americans and blacks had higher insulin values than whites. For C-peptide, differences by sex and race-ethnicity paralleled those seen for fasting insulin with the exception that black men had significantly lower C-peptide values than whites and Mexican Americans. After adjustment for age, fasting plasma glucose (FPG), body mass index (BMI), and waist-to-hip ratio (WHR), the higher levels for insulin in blacks and Mexican Americans remained; both black men and women had significantly lower C-peptide values than whites and Mexican Americans. The molar ratio of fasting C-peptide to fasting insulin was similar for men and women in each race-ethnic group. However, blacks had substantially lower ratios than whites and Mexican Americans.

CONCLUSIONS

We found wide variations in fasting insulin and fasting C-peptide levels by race and ethnicity in US adults that were not explained by confounding factors, primarily measures of obesity. Most notably, the higher fasting insulin and lower fasting C-peptide levels in blacks implies that there is a derangement in insulin clearance and an impairment in beta-cell function in blacks compared with whites and Mexican Americans.

Efficacy and safety of rosiglitazone plus metformin in Mexicans with type 2 diabetes

BACKGROUND

Type 2 diabetes is a growing problem in Mexico. The present study was undertaken to evaluate the efficacy and safety of rosiglitazone 2 mg or 4 mg twice daily (bd) in combination with metformin 2.5 g/day in Mexican patients whose type 2 diabetes was inadequately controlled with metformin alone.

METHODS

This randomized, double-blind, placebo-controlled study was conducted at four centers in Mexico. A total of 116 patients were randomized to metformin 2.5 g/day plus placebo (n=39), metformin 2.5 g/day plus rosiglitazone 2 mg bd (n=37), or metformin 2.5 g/day plus rosiglitazone 4 mg bd (n=40) for 26 weeks.

RESULTS

Mean hemoglobin A(1c) (HbA(1c)) levels decreased significantly from baseline to Week 26 in the rosiglitazone 2 mg bd (-0.7%; p=0.0052) and 4 mg bd (-1.2%; p=0.0008) groups, but increased in the placebo group (+0.3%; p=0.2651). Mean fasting plasma glucose and fructosamine levels also improved significantly with metformin plus rosiglitazone therapy in a dose-ordered manner compared with placebo (p<or=0.0019 and p=0.0006, respectively). C-peptide and immunoreactive insulin levels were decreased from baseline in both rosiglitazone groups. Although mean increases in total cholesterol, low-density lipoprotein (LDL)-cholesterol, and high-density lipoprotein (HDL)-cholesterol were observed in the rosiglitazone groups, the total cholesterol:HDL-cholesterol ratio remained unchanged. The proportion of patients with one or more adverse events was similar across all three groups. There were no cases of hepatotoxicity.

CONCLUSION

Addition of rosiglitazone 2 mg bd and 4 mg bd to metformin therapy improved glycemic control in Mexican patients whose type 2 diabetes was inadequately controlled by metformin alone. Furthermore, the combination of rosiglitazone plus metformin was well tolerated.

Insulin, insulin propeptides and intima-media thickness in the carotid artery in 58-year-old clinically healthy men. The Atherosclerosis and Insulin Resistance study (AIR)

AIMS

To examine the relationship between specific (intact) insulin, insulin propeptides and subclinical atherosclerosis.

METHODS

A cross-sectional study based on a stratified sampling of randomly selected, clinically healthy 58-year-old men (n = 391). Ultrasound examinations of the carotid arteries were performed with measurement of intima-media thickness (IMT) in the common carotid artery and in the carotid artery bulb. Fasting, cross-reacting plasma insulin (RIA), specific (intact) insulin, proinsulin, 32,33 split proinsulin and C-peptide were measured.

RESULTS

Plasma concentrations of cross-reacting plasma insulin, specific insulin, proinsulin, 32,33 split proinsulin and C-peptide were univariately associated with common carotid artery IMT. Established risk factors such as blood pressure, smoking, apoB, triglycerides, body mass index (BMI), and waist--hip ratio were also related to IMT. After adjustment for smoking, apoB, blood pressure and triglycerides, cross-reacting plasma insulin, proinsulin and C-peptide but not specific insulin and split 32,33 proinsulin remained associated with carotid artery IMT. No associations remained after adjustment for BMI.

CONCLUSIONS

Fasting plasma proinsulin, C-peptide, and insulin by cross-reacting RIA was associated with common carotid artery IMT independent of several conventional risk factors for atherosclerosis. The multicollinearity between the insulin peptides and propeptides makes it difficult to clarify the exact role of each peptide.

Associação da cor da pele com diabetes mellitus tipo 2 e intolerância à glicose em mulheres obesas de Salvador, Bahia

Fora do Brasil a prevalência de diabetes mellitus (DM) tipo 2 é maior em negros do que em brancos. Mulheres do ambulatório de obesidade do Hospital Universitário Professor Edgard Santos, Salvador - BA, foram estudadas para avaliar se a cor de pele escura tem prevalência mais alta de DM tipo 2 e de intolerância à glicose (ITG), com diagnóstico baseado nos critérios da Organização Mundial da Saúde, independentemente da idade e do índice de massa corporal (IMC). A cor da pele foi classificada como clara (n= 166), intermediária (n= 186) ou escura (n= 128). Determinou-se o nível de glicose plasmática pelo método da glicose-oxidase. O teste de tolerância à glicose oral foi realizado em todas as pacientes, com exceção de 14 que já sabiam ser diabéticas. Pacientes com pele clara, intermediária e escura foram semelhantes em idade, IMC e relação cintura/quadril. A prevalência de DM, contudo, foi significantemente maior (p< 0,05) nas de pele escura (13,3%) quando comparadas com as de pele clara (7,2%). A prevalência de ITG foi também maior, embora estatisticamente não significante (p= 0,088), nas de pele escura (18,8%) do que nas de pele clara (12,7%). A relação entre o número de pacientes com e sem o diagnóstico de DM ou ITG foi 1,9 vezes maior no grupo pele escura, comparado com clara [odds ratio (OR)= 1,9; intervalo de confiança (IC) 95%= 1,1-3,2; p< 0,05]. Esta associação não foi alterada (OR= 1,7; IC 95%= 1,0-2,9) e permaneceu moderadamente significante (p= 0,069), mesmo após o ajuste para idade e IMC, através de regressão logística. Neste estudo, as mulheres obesas com pele escura tiveram maior associação com DM e ITG, independentemente da idade e IMC.

Syndrome X in children: Influence of ethnicity and visceral fat

Syndrome X, the clustering of risk factors for cardiovascular disease, is recognized as an obesity-related health concern among adults. In particular, individuals with visceral (intra-abdominal) obesity are prone to developing syndrome X. Although extremes of visceral fat have been detected in prepubertal children, the extent to which visceral fat contributes to the development of disease risk factors in children is not known. This review addresses the occurrence of syndrome X and its antecedents in the pediatric population, as well as two specific issues regarding syndrome X in children: the roles of ethnicity and visceral fat. The central feature to emerge from most studies is that basal and post-challenge insulin are significantly higher in African-American, Mexican-American, and Pima Indian children compared to Caucasian children. Although these ethnic differences are independent of adiposity, adiposity is associated with greater insulin in all ethnic groups examined. Mexican-Americans have a higher lipid risk factor level, which is related to greater obesity, and African-Americans have lesser lipid-associated risk, independent of obesity. African-American children may be more likely to develop type 2 diabetes due to obesity-independent hyperinsulinemia and insulin resistance, but appear less predisposed to the obesity-related clustering of risk factors associated with syndrome X. Mexican-American children may be more likely to develop syndrome X due to greater obesity-related hyperinsulinemia and dyslipidemia. Total body fat, rather than visceral fat, appears be the primary determinant of insulin resistance prior to puberty. However, visceral adipose tissue is uniquely related to both insulin and lipid risk factors in children and adolescents, and thus may contribute to the development of the early stages of syndrome X. Am. J. Hum. Biol. 11:249-257, 1999. Copyright 1999 Wiley-Liss, Inc.

Anti-lipolytic effects of insulin in African American and white prepubertal boys

OBJECTIVE

Relative to whites, African Americans have lower circulating triglycerides (TG) and greater highdensity lipoprotein cholesterol. The metabolic basis for this difference is not known. This study was conducted to test the hypothesis that insulin-induced suppression of free fatty acids (FFA) results in lower serum TG in African American versus white prepubertal children.

RESEARCH METHODS AND PROCEDURES

Insulin, FFA, and TG were determined at baseline and during a frequently sampled, intravenous glucose tolerance test in eight African American and eight white prepubertal males pair-matched for whole-body insulin sensitivity.

RESULTS

Baseline TG was lower in African Americans (0.43 +/- 0.10 vs. 0.79 +/- 0.37 mM/L; mean +/- SD; p < 0.01). African Americans had higher peak insulin (218 +/- 102 vs. 100 +/- 30 pM/L; mean +/- SD; p < 0.01) and a greater acute insulin response (9282 +/- 4272 vs. 4230 +/- 1326 pM/L x 10 minutes; mean +/- SD; p < 0.05). FFA and TG values determined at the FFA nadir were lower in African Americans (0.26 +/- 0.02 vs. 0.30 +/- 0.03 mEq/L; mean +/- SD; p < 0.01 for FFA nadir and 0.49 +/- 0.07 vs. 0.77 +/- 0.33 mM/L; mean +/- SD; p < 0.05 for TG). Among all subjects, FFA nadir was correlated with peak insulin (r = -0.54; p < 0.05). After adjusting for FFA nadir, neither baseline nor postchallenge TG differed with ethnicity (p = 0.073 and 0.192, respectively). The ethnic difference in FFA nadir disappeared after adjusting for peak insulin (p = 0.073).

DISCUSSION

These data suggest that hyperinsulinemiainduced suppression of FFA among African Americans is a determinant of lower TG in this group.

Insulin resistance and intima-media thickness in the carotid and femoral arteries of clinically healthy 58-year-old men. The Atherosclerosis and Insulin Resistance Study (AIR)

OBJECTIVE

To examine whether insulin resistance was associated with ultrasound-assessed measures of atherosclerosis in men with varying degrees of obesity.

DESIGN

A random selection of subjects from the general population were divided into quintiles of a body mass index/blood glucose score that was shown to be a valid and reproducible index of the degree of insulin sensitivity as assessed by the clamp technique. Every fourth man in quintiles 1 and 5 and every 20th man in quintiles 2-4 (in total, 104 men) were selected for an ultrasound examination of the carotid and femoral arteries and a euglycaemic hyperinsulinaemic clamp examination, adjusted for fat-free mass.

SETTING

A university hospital.

SUBJECTS

A total of 104 clinically healthy 58-year-old men of Swedish ancestry.

RESULTS

The mean common carotid artery intima-media thickness (IMT), but not the common femoral IMT, correlated significantly with glucose infusion rate (GIR) (r = - 0.20, P < 0.05), systolic blood pressure (r = 0.20, P < 0.05), pulse pressure (r = 0.23 P < 0.01), heart rate (r = 0.20, P < 0.05), HDL cholesterol (r = - 0.18, P < 0.05), log triglycerides (r = 0.28, P < 0.01), apoA1 (r = - 0.20, P < 0.05), apoB (r = 0.21, P < 0.05), LDL particle size (r = - 0.22, P < 0.05) and plasma insulin (r = 0.20, P < 0.05). In a multiple regression, common carotid IMT was independently associated with log triglycerides (beta = 0.25, P = 0.012) and pulse pressure (beta = 0.21, P = 0.031) (R2 = 8.7%, P = 0.005)

CONCLUSIONS

Insulin sensitivity, measured with the gold standard euglycaemic hyperinsulinaemic clamp method, showed similar associations with ultrasound-assessed measures of atherosclerosis in the carotid arteries as established cardiovascular risk factors, but only triglycerides and pulse pressure contributed independently to the variability in the common carotid intima-media thickness.

Comparison of risk factors for obesity in young, nonobese African-American and Caucasian women

OBJECTIVE

To determine whether specific risk factors for obesity were more evident in young, normal-weight African-American (AA) compared to Caucasian-American (CA) women.

DESIGN

Cross-sectional age-matched study.

SUBJECTS

Young, nonobese, sedentary AA (n= 13, 22.5y of age, 23.6% body fat) and CA women (n = 11, 21.5y of age, 24.0% body fat).

MEASUREMENTS

Aerobic physical fitness (peak VO2), resting metabolic rate (RMR), resting and submaximal exercise fat oxidation rates, total daily energy expenditure (TDEE) by the doubly-labeled water method, physical activity energy expenditure (PAEE), skeletal muscle glycolytic (phosphofructokinase activity (PFK)) and beta-oxidative (beta-hydroxy-acyl CoA dehydrogenase (beta-HADH)) activity, and insulin sensitivity estimated by the insulin-augmented frequently sampled intravenous glucose tolerance test.

RESULTS

The AA and CA subjects were similar in age, body mass index and body composition, but the AA women exhibited lower peak VO2. There were no group differences in RMR adjusted for body composition, or in the rates of submaximal exercise energy expenditure or fat oxidation, and no difference in skeletal muscle beta-HADH or PFK activity. The AA women exhibited lower insulin sensitivity and greater acute insulin response to glucose. The mean TDEE for the AA women was only 74% that of the CA women, primarily due to a lower physical activity energy expenditure (AA group: xPAEE = 1,246+/-438 kJ/day; CA group: x= 3,310+/-466 kJ/day.

CONCLUSION

These data indicate that PAEE and its correlates of peak aerobic capacity and insulin sensitivity are lower in young, nonobese AA women compared to their CA counterparts.

Racial differences in insulin secretion and sensitivity in prepubertal children: role of physical fitness and physical activity

OBJECTIVE

To investigate in prepubertal children whether physical fitness and/or physical activity are: 1) associated with insulin secretion and sensitivity and 2) account for racial differences in insulin secretion and sensitivity.

RESEARCH METHODS AND PROCEDURES

Subjects included 34 African American and 34 white nondiabetic children aged 5 to 11 years. Data were divided into two sets according to the availability of VO2max and physical activity data. Body composition was measured by dual-energy X-ray absorptiometry. Subcutaneous abdominal adipose tissue and intra-abdominal adipose tissue were examined by computed tomography. Insulin sensitivity (S1) and acute insulin response (AIR) were determined by a frequently sampled intravenous glucose tolerance test. An all-out, progressive treadmill exercise test was used for measuring VO2max. Physical activity data were collected by questionnaire.

RESULTS

African American children had lower SI and higher AIR than white children, after adjusting for total body fat mass. African Americans reported higher levels of physical activity (hours/wk) than whites, but had a lower VO2max. In multiple linear regression analysis, hours/wk of activity and hours/wk of vigorous activity, but not moderate activity, were independently related to SI and AIR after adjusting for race, total body fat mass or fat distribution, and total lean tissue mass. VO2max was not related to AIR, and was inversely related to SI, after adjusting for body composition. Race remained significantly associated with both SI and AIR, even after adjusting for body composition, fat distribution, and hours/wk of activity or hours/wk of vigorous activity.

DISCUSSION

In summary, overall physical activity and, especially, vigorous activity were associated with insulin secretion and sensitivity. However, neither physical activity nor VO2max explained the racial difference in insulin secretion (higher in African Americans) and sensitivity (lower in African Americans). Thus, racial (African American to white) differences in aspects of insulin action seem to be due to factors other than body composition, fat distribution, cardiovascular fitness, and amount of physical activity.

Chronic subclinical inflammation as part of the insulin resistance syndrome: the Insulin Resistance Atherosclerosis Study (IRAS)

BACKGROUND

Inflammation has been suggested as a risk factor for the development of atherosclerosis. Recently, some components of the insulin resistance syndrome (IRS) have been related to inflammatory markers. We hypothesized that insulin insensitivity, as directly measured, may be associated with inflammation in nondiabetic subjects.

METHODS AND RESULTS

We studied the relation of C-reactive protein (CRP), fibrinogen, and white cell count to components of IRS in the nondiabetic population of the Insulin Resistance Atherosclerosis Study (IRAS) (n=1008; age, 40 to 69 years; 33% with impaired glucose tolerance), a multicenter, population-based study. None of the subjects had clinical coronary artery disease. Insulin sensitivity (S(I)) was measured by a frequently sampled intravenous glucose tolerance test, and CRP was measured by a highly sensitive competitive immunoassay. All 3 inflammatory markers were correlated with several components of the IRS. Strong associations were found between CRP and measures of body fat (body mass index, waist circumference), S(I), and fasting insulin and proinsulin (all correlation coefficients >0.3, P<0.0001). The associations were consistent among the 3 ethnic groups of the IRAS. There was a linear increase in CRP levels with an increase in the number of metabolic disorders. Body mass index, systolic blood pressure, and S(I) were related to CRP levels in a multivariate linear regression model.

CONCLUSIONS

We suggest that chronic subclinical inflammation is part of IRS. CRP, a predictor of cardiovascular events in previous reports, was independently related to S(I). These findings suggest potential benefits of anti-inflammatory or insulin-sensitizing treatment strategies in healthy individuals with features of IRS.

Risk of type 2 diabetes mellitus in young adults from a biracial community: the Bogalusa Heart Study

BACKGROUND

Since type 2 diabetes has a strong familial component, characteristics of young adult offspring of type 2 diabetics were examined in a community sample to determine early abnormalities in black and white persons at risk.

METHODS

The sample consisted of 1,338 fasting young adults (72% white, 28% black) aged 19 to 37 years from a biracial community, including those with positive parental history of type 2 diabetes (one offspring per family, n = 230) or conditions of impaired fasting glucose and type 2 diabetes (n = 22).

RESULTS

Positive family history of diabetes or impaired fasting glucose and type 2 diabetes in young adults of both races were significantly associated with adverse profiles of measures of obesity and abdominal fat (body mass index, triceps and subscapular skinfolds, waist circumference, and abdominal height), systolic and diastolic blood pressures, serum total cholesterol, triglycerides, VLDL cholesterol, and HDL cholesterol, and indicators of glucose homeostasis (plasma glucose and insulin and insulin resistance index). The magnitude of the differences in obesity and abdominal fat measures and plasma glucose between individuals with and without parental diabetes was greater among blacks versus whites (P = 0. 047-0.004). Further, black offspring of both diabetics and non-diabetics had unfavorable profiles of obesity and abdominal fat measures, blood pressure, insulin, and insulin resistance index (P = 0.0001). In a multivariate analysis, adiposity measured as body mass index (P = 0.03) and plasma glucose (P = 0.003) emerged as the two independent characteristics that distinguished those with parental diabetes from those without parental disease. Insulin (P = 0.0001) and the insulin resistance index (P = 0.0001) were independently associated with conditions of impaired fasting glucose or type 2 diabetes.

CONCLUSIONS

The risk factors of young adults with parental type 2 diabetes or conditions of impaired fasting glucose and type 2 diabetes can be detected early. These observations have implications for early prevention and intervention, especially for blacks.

Relation of generalized and central obesity to cardiovascular risk factors and prevalent coronary heart disease in a sample of American Indians: the Strong Heart Study

OBJECTIVE

To examine the hypothesis linking measures of obesity including body mass index (BMI), waist circumference (waist) and percentage body fat to coronary heart disease (CHD) prevalence and its risk factors in American Indians.

DESIGN

The Strong Heart Study assesses the prevalence of CHD and its risk factors in American Indians in Arizona, Oklahoma and South/North Dakota. Participants underwent a physical examination and an electrocardiogram; anthropometric and blood pressure measurements were taken, as were measurements of glucose, lipoproteins, fibrinogen, insulin, hemoglobin A1c and urinary albumin.

PARTICIPANTS

Data were available for 4549 men and women between 45 and 74 y of age.

MEASUREMENTS

Obesity, measured using body mass index, waist circumference and percentage body fat, was correlated with prevalent CHD and its risk factors.

RESULTS

More than 75% of participants were overweight (BMI>25 kg/m2). Measures of obesity were greater in women than in men, in younger than in older participants, and in participants with diabetes than in nondiabetic participants. CHD risk factors were associated with measures of obesity but, except for insulin concentration, changes in metabolic variables with increasing obesity were small. Associations were not stronger with waist than with BMI. The prevalence of CHD in those whose BMI and/or waist measurements lay in the lowest and highest quintiles, by gender and diabetic status, was similar.

CONCLUSIONS

Although CHD risk factors are associated with obesity in American Indians, distribution of obesity (ie waist) is no more closely related to risk factors than is generalized obesity (ie BMI), and changes in CHD risk factors with obesity were small. Thus, the relations among obesity, body fat distribution and CHD risk may differ in this population.

Association of diabetes, serum insulin, and C-peptide with gallbladder disease

An inconsistent association has been found between gallbladder disease and diabetes mellitus. We hypothesized that insulin resistance rather than diabetes status may be a primary factor involved in gallstone formation. A total of 5,653 adult participants in the third United States National Health and Nutrition Examination Survey without known diabetes underwent gallbladder ultrasonography and phlebotomy after an overnight fast for measurement of serum insulin, C-peptide, and glucose. Gallbladder disease was defined as ultrasound-documented gallstones or evidence of cholecystectomy. Subjects were characterized as having normal fasting glucose (<110 mg/dL), impaired fasting glucose (110 to <126 mg/dL), or undiagnosed diabetes (>/=126 mg/dL). After controlling for other known gallbladder disease risk factors, among women, undiagnosed diabetes was associated with increased risk of gallbladder disease (prevalence ratio [PR] = 1.91, 95% confidence interval [CI] = 1.29-2. 83); whereas impaired fasting glucose was unassociated. Gallbladder disease risk in women increased with levels of fasting insulin (PR = 1.63, 95% CI = 1.11-2.40) and C-peptide (PR = 2.07, 95% CI = 1.32-3. 25) comparing highest to lowest quintiles. However, the association of gallbladder disease with undiagnosed diabetes was not diminished when the model included fasting insulin (PR = 1.85, 95% CI = 1.24-2. 77). In men, there was a statistically nonsignificant association with undiagnosed diabetes (PR = 2.11, 95% CI = 0.76-5.85), but no association of gallbladder disease with insulin or C-peptide. Among women higher fasting serum insulin levels increased the risk of gallbladder disease, but did not account for the increased risk in persons with diabetes.

Type II diabetes mellitus: no longer just adults

Type II diabetes mellitus is no longer exclusively a disease of adults. Health care professionals and agencies must gain a better understanding of (1) the epidemiology of type II diabetes mellitus in childhood; (2) the phenotypic, biochemical, metabolic, and autoimmune characteristics at diagnosis and during the course of the disease; (3) therapeutic modalities; (4) screening of high-risk populations; and (5) prevention strategies. This will be one of the challenges in pediatric diabetes as we approach the 21st century.

Systemic resistance to the antilipolytic effect of insulin in black and white women with visceral obesity

This study was designed to determine the role of visceral adipose tissue (VAT) accumulation in systemic fat metabolism and to compare this in black and white women who differ in their manifestations of upper body obesity. Systemic glycerol and free fatty acid (FFA) turnover rates (rates of appearance, Ra) were measured in the basal state and during a pancreatic euglycemic clamp in nondiabetic, premenopausal, obese black and white women with a wide range of VAT accumulation. The slopes of the regression equations predicting basal and insulin-suppressed RaGlycerol and RaFFA from VAT area, age, and fat mass or fat-free mass did not significantly differ between black and white women. VAT area was the best predictor of the %-suppressed RaGlycerol and RaFFA during the pancreatic clamp (partial r = 0.76, P < 0.0001 and partial r = 0.60, P < 0.05, respectively). Basal R(a)Glycerol, but not RaFFA, was lower in black than in white women (P < 0.05). During the clamp, black women showed greater insulin suppression of RaGlycerol than of RaFFA (P < 0.0001) and greater insulin suppression of RaGlycerol (P < 0. 05) but similar suppression of RaFFA compared with white women. These differences were independent of age, fat mass, or fat-free mass and were partly explained by a lower VAT in black women. Thus, in both races, VAT accumulation was associated with systemic resistance to the antilipolytic effect of insulin and, in obese black women, systemic lipolysis measured as glycerol turnover rate was more responsive to insulin suppression than were systemic FFA turnover rates.

LDL size in African Americans, Hispanics, and non-Hispanic whites : the insulin resistance atherosclerosis study

The prevalence of cardiovascular disease (CVD) and atherosclerosis varies among several minority ethnic groups in the United States. Recently, small, dense low density lipoprotein (LDL) particle size has been recognized as a risk factor for CVD. We examined LDL size as a possible explanation for differences in CVD rates in 1571 subjects from the Insulin Resistance Atherosclerosis Study (IRAS), a multiethnic study of insulin resistance and cardiovascular risk factors. LDL size (A) was significantly different by ethnic group (African Americans 262.1+/-0.6, Hispanics 257.6+/-0.6, and non-Hispanic whites 259.2+/-0.4, P<0.001). Ethnic differences in LDL size continued to be statistically significant after adjustment for upper body adiposity, insulin resistance, and glucose tolerance status. However, after further adjustment for other cardiovascular risk factors, especially ethnic differences in triglyceride and high density lipoprotein (HDL) cholesterol levels, the ethnic differences in LDL size were markedly attenuated and in general no longer statistically significant. The relation of triglyceride, HDL cholesterol, insulin resistance, and adiposity to LDL size in each ethnic group was similar. LDL size differs by ethnic group, which is independent of obesity or insulin resistance. These ethnic differences appear to be due to ethnic variations in dyslipidemia (especially differences in triglyceride levels); ethnic differences in LDL size are not consistent with previously reported ethnic dissimilarities in CVD or atherosclerosis.

Using 3 data sources and methods to shape a nutrition campaign

The first objective of this research was to define a target population of African-American women more clearly. The second was to provide specific information about the needs and preferences of that population in order to design an effective, culturally relevant, community-based communications campaign to promote more healthful lifestyles. Data collection and analysis included the following: interviews with 10 community nutritionists and the director of the State Office of Nutrition, 6 focus groups with a total of 47 members of the target population, and direct observation and documentation of key community resources. This approach, called "triangulation," permits more in-depth understanding of issues, provides different perspectives on the problem, and helps ensure accuracy of conclusions. Interviews with nutritionists identified young African-American women as the appropriate target population for the campaign. These interviews and the focus-group discussions confirmed the acceptability of higher weight and better body-esteem among African-American women than among white women. Both the nutritionists and the focus-group members identified the need and desire for information and skills related to food preparation and provided specific direction for program content. Community observation confirmed the need for food markets with merchandise of consistently high quality, especially in the fresh and frozen produce sections. Observation also helped identify community services and programs. The 3 sets of data, which augmented a comprehensive literature review, provided a firm foundation for the campaign's design and development. Dietitians and nutritionists working in community settings can use triangulation to gain a better understanding of their populations in order to develop more effective interventions.

The multidimensional nature of renal disease: rates and associations of albuminuria in an Australian Aboriginal community

BACKGROUND

An epidemic of end-stage renal disease (ESRD) is accompanying the rising rates of hypertension, type 2 diabetes and cardiovascular disease among Aborigines in the Northern Territory of Australia. Incidence rates are now 21 times those of nonAboriginal Australians and are doubling every four years. We describe the rates and associations of renal disease in one remote community, which has a current ESRD incidence of 2700 per million, and cardiovascular mortality among the highest in Australia.

METHODS

Between 1992 and 1995 a community-wide screening program was conducted, in which the urinary albumin/creatinine ratio (ACR) was used as the chief renal disease marker. More than 90% of the population ages five and older participated.

RESULTS

Albuminuria was evident in early childhood and increased dramatically with age; 26% of adults had microalbuminuria and 24% had overt albuminuria. All renal failure developed out of a background of overt albuminuria. ACR was significantly correlated with the presence of scabies at screening, with a history of poststreptococcal glomerulonephritis, which is epidemic and endemic in the community, with increasing body wt, blood pressure, glucose, insulin and lipid levels, and with evidence of heavy drinking. ACR was also significantly and inversely correlated with birth weight. As a result of its association with deteriorating hemodynamic and metabolic profiles, increasing ACR was also correlated with increasing cardiovascular risk score. Direct observations showed, and multivariate models predicted, progressive amplification of ACR when multiple risk factors were present simultaneously. Albuminuria also clustered in families.

CONCLUSION

Renal disease in this population is multifactorial, with risk factors related to whole-of-life nutrition, metabolic and hemodynamic profiles, infections, health behaviors, and possibly a family predisposition. Its relationship to low birth weight, and its associations with deteriorating metabolic and hemodynamic profiles, suggest that renal disease is, in part, a component of Syndrome X, which explains the simultaneous increase in metabolic, cardiovascular and renal disease in Aboriginal people. The family clustering might have both environmental and genetic causes, and is under further investigation. Most of the identified risk factors arise out of poverty, disadvantage and accelerated lifestyle change, and the current epidemic can be explained by the confluence of many risk factors in the last few decades. The introduction of effective and sustained programs to address social, economic and educational inequities in all Aboriginal communities, and of screening and renal- and cardiovascular-protective treatment programs for those already afflicted are matters of great urgency.

Proinsulin and insulin concentrations in relation to carotid wall thickness: Insulin Resistance Atherosclerosis Study

BACKGROUND AND PURPOSE

Insulin resistance and hyperinsulinemia have been associated with atherosclerosis. Recent attention has focused on the possible role of proinsulin because most radioimmunoassays for insulin cross-react with proinsulin. Therefore, it is not known which of the two, insulin per se or proinsulin, is more strongly related to atherosclerosis.

METHODS

We examined the relation between fasting proinsulin, fasting split proinsulin, fasting and 2-hour insulin (after oral glucose load), and intima-media wall thickness (IMT) in the common carotid artery (CCA) and internal carotid artery (ICA) in 985 nondiabetic subjects from the Insulin Resistance Atherosclerosis Study, a multiethnic study of insulin resistance and atherosclerosis.

RESULTS

In the overall population, a weak but significant relation between proinsulin and CCA IMT was observed (r=0.07, P=0.029). However, the relation between proinsulin and IMT was stronger in Hispanics and non-Hispanic whites than in African Americans. In non-Hispanic whites and Hispanics, significant correlations between CCA and proinsulin (r=0.087) and between ICA and proinsulin (r=0.101), split proinsulin (r = 0.092), and fasting insulin (r = 0.087) were observed. The significant correlations became more attenuated (and nonsignificant) after adjustment for cardiovascular risk factors, especially plasminogen activator inhibitor-1 (PAI-1).

CONCLUSIONS

The association between proinsulin and IMT, while weak, appears to be stronger than the association between insulin and IMT. Adjustment for PAI-1 markedly attenuated the association between proinsulin and IMT, suggesting a possible mediating role for PAI-1 in this association. It is possible that proinsulin may represent a marker of atherosclerosis rather than a causal factor for atherosclerosis. Studies of the insulin resistance syndrome and atherosclerosis that use insulin as a surrogate for insulin resistance should consider the use of specific insulin assays as well as determination of proinsulin concentrations.

Fat distribution and insulin response in prepubertal African American and white children

Ethnic differences in obesity-related disease prevalence may relate to differences in fat distribution or metabolism. We conducted a study in 73 African American and white children to examine the relation between fat distribution and insulin and to determine whether ethnic differences in fat distribution or in adiposity-insulin relations contribute to differences in insulin concentrations. Fasting and postchallenge insulin concentrations were determined by oral-glucose-tolerance test, total body fat by dual-energy X-ray absorptiometry, and subcutaneous abdominal (SAAT) and intraabdominal (IAAT) adipose tissue by computerized tomography. African Americans had greater fasting insulin (x +/- SD: 79 +/- 37 compared with 55 +/- 23 pmol/L, P < 0.01), incremental 30-min insulin (567 +/- 438 compared with 300 +/- 304 pmol/L, P < 0.001), and incremental area under the insulin curve (AUC; 262 +/- 209 compared with 164 +/- 156 pmol/L, P < 0.01). In multiple linear regression, fasting insulin was independently related to total fat within both ethnic groups (model R2 = 0.42 and 0.52 for African Americans and whites, respectively), incremental 30-min insulin to total fat and IAAT in whites only (model R2 = 0.71), and AUC to SAAT in African Americans only (model R2 = 0.49). Adjusting insulin indexes for adiposity did not eliminate the significant effect of ethnicity. In general, relations between adiposity and insulin were stronger in whites than in African Americans. African American children had higher insulin concentrations than white children after total body fat, IAAT, and SAAT were controlled for. However, strong relations between adiposity (total and abdominal) and insulin in both groups suggest that obesity may contribute to disease risk regardless of ethnicity.

Cardiovascular disease insulin risk in Mexican-American and Anglo-American children and mothers

OBJECTIVE

To evaluate the relationship between insulin levels and cardiovascular risk factors in children and determine whether it varies among ethnic groups.

METHODS

Cardiovascular risk factors and insulin levels were compared in 144 Mexican-American and Anglo-American mother-child pairs, when the children were 11 years of age.

RESULTS

Although mean age did not differ between ethnicities, Mexican-American mothers and children both had a greater body mass index (mothers: 29.2 +/- 6.2 vs 27.2 +/- 7.9; children: 21.7 +/- 4.7 vs 19.7 +/- 4.6) and sum of skinfolds than did Anglo-Americans. Triglycerides, very low-density lipoprotein cholesterol, fasting insulin, and cholesterol/high-density lipoprotein ratio were higher, while high-density lipoprotein cholesterol was lower in both Mexican-American adults and children compared with Anglo-Americans. After adjusting for measures of obesity, only high-density lipoprotein cholesterol levels remained significantly lower in Mexican-Americans. For both adults and children, higher quartiles of insulin levels were associated with significantly higher triglycerides, blood pressure and lower high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol/apolipoprotein B levels (estimate of dense low-density lipoprotein size). A summary variable representing cardiovascular risk factors present in adult syndrome X patients was higher in both Mexican-American adults and children than in Anglo-Americans.

CONCLUSION

Mexican-American children and adults have higher levels of many cardiovascular risk factors, and this appears related to higher insulin levels and overweight. Appropriate nutrition, weight control, and exercise at early ages could be important in slowing the development of atherosclerosis.

Insulin secretion and sensitivity in healthy African-American vs American white children

Racial differences in insulin secretion and insulin sensitivity in healthy children were studied by administering a 2-hour hyperglycemic clamp (225 mg/dL) to 14 black and 16 white healthy adolescents (Tanner II-V), and 12 black and 11 white prepubertal children, matched for age, body mass index, and Tanner I pubertal development. In prepubertal children, fasting and first-phase insulin concentrations were higher in blacks compared with whites (14.7+/-1.3 vs 10.4+/-1.2, P=0.02, and 76.9+/-6.8 vs 52.1+/-6.4 microu/mL, P=0.016). There were no differences in second-phase insulin levels and insulin sensitivity index. In pubertal adolescents, first-phase and second-phase insulin concentrations were higher in blacks compared with whites (first-phase: 157.3+/-18.3 vs 77.0+/-8.7 microu/mL, P=0.0003; second-phase: 175.0+/-24.3 vs 108.7+/-8.8 microu/mL, P=0.012). Insulin sensitivity index was 35% lower in black adolescents compared with whites (P=0.02). These findings indicate that significant differences in insulin secretion and sensitivity are detectable early in childhood in healthy African-American vs American whites. However, genetic (race) vs environmental factors (physical activity/fitness, energy balance) should be carefully scrutinized as potential factors responsible for such differences.

Progress in population analyses of the insulin resistance syndrome

Insulin resistance is associated with a variety of cardiovascular risk factors including hypertension, dyslipidemia, and non-insulin-dependent diabetes. In blacks, the relation between insulin resistance, hypertension, and atherosclerosis has been questioned. Most data collected on the Insulin Resistance Syndrome have been collected in nondiabetic subjects; therefore, no inference can be drawn to exogenous insulin use in diabetic subjects where improved glycemic control is usually associated with improved cardiovascular risk factors (especially dyslipidemia) in the absence of weight gain.

Insulin resistance implications for type II diabetes mellitus and coronary heart disease

PURPOSE

To review information on the implications of insulin resistance for type II diabetes mellitus (non-insulin-dependent diabetes mellitus) and coronary heart disease, and to derive guidance from this information for the management of these conditions.

DATA SOURCES

A MEDLINE search of English-language articles published between 1985 and July 1996, and review of the bibliographies of articles obtained through the MEDLINE search and textbooks.

STUDY SELECTION

Primary research articles, reviews and perspectives on the epidemiology of diabetes and cardiovascular diseases and on intervention outcomes in these diseases.

DATA EXTRACTION

Study design and quality were assessed, with particular attention to methods, study population size and other characteristics. Conclusions of review articles and perspectives were analyzed critically.

DATA SYNTHESIS

Type II diabetes is associated with a two- to fourfold excess of coronary heart disease, compared to nondiabetic populations. In most studies, glycemia and duration of clinical diabetes were found to be only weak risk factors for coronary heart disease. Conventional coronary heart disease risk factors such as dyslipidemia and hypertension have been associated with coronary heart disease in type II diabetes subjects. Hyperinsulinemia and insulin resistance have been predictive of the development of type II diabetes and, in some studies, of coronary heart disease.

CONCLUSION

Strategies to prevent the development of coronary heart disease in diabetic and possibly prediabetic subjects should emphasize a multifactorial approach, including: a) improved glycemic control; b) aggressive treatment of risk factors for coronary heart disease, including insulin resistance; c) primary prevention of NIDDM; and d) use of glucose lowering agents that improve insulin sensitivity and cardiovascular risk factors.

Ethnic differences in carotid wall thickness. The Insulin Resistance Atherosclerosis Study

BACKGROUND AND PURPOSE

Ethnic differences in cardiovascular disease (CVD) morbidity and mortality have been observed in US adults. However, little data exist on differences in indices of preclinical atherosclerosis such as carotid wall intima-media thickness (IMT) for US non-Hispanic whites, Hispanics, and blacks. This study was undertaken to determine whether there were ethnic differences in carotid wall IMT.

METHODS

Internal carotid artery (ICA) IMT and common carotid artery (CCA) IMT, indices of atherosclerosis, were assessed with the use of B-mode ultrasound in 1020 nondiabetic participants in the Insulin Resistance Atherosclerosis Study, a multicenter study designed to examine the association between insulin resistance and carotid atherosclerosis. The study included 281 blacks, 329 Hispanics, and 410 non-Hispanic whites aged 40 to 69 years.

RESULTS

Blacks had significantly greater CCA IMT than non-Hispanic whites (865 versus 808 microns); this remained significant after adjustment for major CVD risk factors and insulin sensitivity (864 versus 823 microns). There were no significant differences in ICA IMT between blacks and non-Hispanic whites. Hispanics had significantly lesser CCA IMT than non-Hispanic whites (749 versus 776 microns), and these differences remained significant after adjustment for traditional cardiovascular risk factors and insulin sensitivity (750 versus 778 microns). There were no significant differences in ICA IMT between non-Hispanic whites and Hispanics.

CONCLUSIONS

We conclude that ethnic differences exist in CCA but not in ICA IMT in nondiabetic subjects. These differences in IMT, which are indicators of atherosclerosis, are a non-invasive measure that is consistent with some of the data on clinical end points. These differences may be associated with the observed differences in CVD morbidity and mortality among major ethnic groups in the United States.