Differential impact of obesity on glucose metabolism in black and white American adolescents

Black African men with early type 2 diabetes have similar muscle, liver and adipose tissue insulin sensitivity to white European men despite lower visceral fat

AIMS/HYPOTHESIS

Type 2 diabetes is more prevalent in black African than white European populations although, paradoxically, black African individuals present with lower levels of visceral fat, which has a known association with insulin resistance. Insulin resistance occurs at a tissue-specific level; however, no study has simultaneously compared whole body, skeletal muscle, hepatic and adipose tissue insulin sensitivity between black and white men. We hypothesised that, in those with early type 2 diabetes, black (West) African men (BAM) have greater hepatic and adipose tissue insulin sensitivity, compared with white European men (WEM), because of their reduced visceral fat.

METHODS

Eighteen BAM and 15 WEM with type 2 diabetes underwent a two-stage hyperinsulinaemic-euglycaemic clamp with stable glucose and glycerol isotope tracers to assess tissue-specific insulin sensitivity and a magnetic resonance imaging scan to assess body composition.

RESULTS

We found no ethnic differences in whole body, skeletal muscle, hepatic or adipose tissue insulin sensitivity between BAM and WEM. This finding occurred in the presence of lower visceral fat in BAM (3.72 vs 5.68 kg [mean difference -1.96, 95% CI -3.30, 0.62]; p = 0.01). There was an association between skeletal muscle and adipose tissue insulin sensitivity in WEM that was not present in BAM (r = 0.78, p < 0.01 vs r = 0.25 p = 0.37).

CONCLUSIONS/INTERPRETATION

Our data suggest that in type 2 diabetes there are no ethnic differences in whole body, skeletal muscle, hepatic and adipose tissue insulin sensitivity between black and white men, despite differences in visceral adipose tissue, and that impaired lipolysis may not be contributing to skeletal muscle insulin resistance in men of black African ethnicity.

Effect of body mass index on diabetogenesis factors at a fixed fasting plasma glucose level

Aim

The present study evaluated the relative influence of body mass index (BMI) on insulin resistance (IR), first-phase insulin secretion (FPIS), second-phase insulin secretion (SPIS), and glucose effectiveness (GE) at a fixed fasting plasma glucose level in an older ethnic Chinese population.

Methods

In total, 265 individuals aged 60 years with a fasting plasma glucose level of 5.56 mmol/L were enrolled. Participants had BMIs of 20.0–34.2 kg/m². IR, FPIS, SPIS, and GE were estimated using our previously developed equations. Pearson correlation analysis was conducted to assess the correlations between the four diabetogenesis factors and BMI. A general linear model was used to determine the differences in the percentage of change among the four factor slopes against BMI.

Results

Significant correlations were observed between BMI and FPIS, SPIS, IR, and GE in both women and men, which were higher than those reported previously. In men, BMI had the most profound effect on SPIS, followed by IR, FPIS, and GE, whereas in women, the order was slightly different: IR, followed by FPIS, SPIS, and GE. Significant differences were observed among all these slopes, except for the slopes between FPIS and SPIS in women (p = 0.856) and IR and FPIS in men (p = 0.258).

Conclusions

The contribution of obesity to all diabetes factors, except GE, was higher than that reported previously. BMI had the most profound effect on insulin secretion in men and on IR in women in this 60-year-old cohort, suggesting that lifestyle modifications for obesity reduction in women remain the most important method for improving glucose metabolism and preventing future type 2 diabetes mellitus.

Adiponectin, Insulin Sensitivity, β-Cell Function, and Racial/Ethnic Disparity in Treatment Failure Rates in TODAY

OBJECTIVE

The Treatment Options for type 2 Diabetes in Adolescents and Youth (TODAY) study demonstrated that glycemic failure rates in the three treatments combined-metformin plus rosiglitazone, metformin alone, and metformin plus lifestyle-were higher in non-Hispanic blacks (NHB; 52.8%) versus non-Hispanic whites (NHW; 36.6%) and Hispanics (H; 45.0%). Moreover, metformin alone was less effective in NHB versus NHW versus H youth. This study describes treatment-associated changes in adiponectin, insulin sensitivity, and β-cell function over time among the three racial/ethnic groups to understand potential mechanism(s) responsible for this racial/ethnic disparity.

RESEARCH DESIGN AND METHODS

TODAY participants underwent periodic oral glucose tolerance tests to determine insulin sensitivity, C-peptide index, and oral disposition index (oDI), with measurements of total and high-molecular-weight adiponectin (HMWA).

RESULTS

At baseline NHB had significantly lower HMWA than NHW and H and exhibited a significantly smaller increase (17.3% vs. 33.7% vs. 29.9%, respectively) during the first 6 months overall. Increases in HMWA were associated with reductions in glycemic failure in the three racial/ethnic groups combined (hazard ratio 0.61, P < 0.0001) and in each race/ethnicity separately. Over time, HMWA was significantly lower in those who failed versus did not fail treatment, irrespective of race/ethnicity. There were no differences in treatment-associated temporal changes in insulin sensitivity, C-peptide index, and oDI among the three racial/ethnic groups.

CONCLUSIONS

HMWA is a reliable biomarker of treatment response in youth with type 2 diabetes. The diminutive treatment-associated increase in HMWA in NHB (∼50% lower) compared with NHW and H may explain the observed racial/ethnic disparity with higher therapeutic failure rates in NHB in TODAY.

Female sex, poverty and globalization as determinants of obesity among rural South African type 2 diabetics: a cross-sectional study

Background

Countries in Sub-Saharan Africa have recently been experiencing increases in the prevalence of obesity, type 2 diabetes mellitus (T2DM) and other non-communicable diseases in both urban and rural areas. Despite their growing influence on population health in the region, there is a paucity of epidemiological studies on the twin epidemic of obesity and T2DM, particularly in the rural communities in South Africa. We investigated the prevalence and the determinants of overall obesity among patients with T2DM in rural and semi-urban areas surrounding the town of Mthatha, South Africa.

Methods

This hospital-based cross-sectional study was conducted among patients with T2DM attending the outpatient department at Mthatha General Hospital, Eastern Cape Province, South Africa. Data were obtained from 327 participants using standardized questionnaires that included items on sex, age, level of education, type of residence, employment status, smoking status, physical activity, diet and alcohol intake. After taking measurements of height and weight, participants were defined as obese if their body mass index exceeded 30 kg/m². Univariate and multivariate logistic regression analyses were performed to identify the determinants of obesity in our sample population.

Results

We found that 60.2% of our sample population were defined as obese. In our univariate analyses, female sex (p < 0.001), age ≥50 years (p = 0.023), rural residence (p < 0.001), excessive alcohol intake (p = 0.002), current cigarette smoking (p < 0.001), level of education (p < 0.001), regular consumption of soft drinks (p < 0.001) and unemployment (p = 0.043) were found to be positively and significantly associated with obesity. In the multivariate logistic regression analysis, female sex (p < 0.001), unemployment (p = 0.012) and level of education (p < 0.001) were found to be independent determinants of obesity.

Conclusion

We found that female sex, educational attainment, unemployment and current cigarette smoking were positively associated with obesity among the study participants. Lifestyle changes, poverty reduction and public education are urgently needed to address the growing obesity epidemic in rural areas of South Africa.

Retrospective chart review of children with type 2 diabetes mellitus evaluating the efficacy of metformin vs. insulin vs. combination insulin/metformin

OBJECTIVES

Type 2 diabetes mellitus is a growing problem in pediatrics and there is no consensus on the best treatment. We conducted this chart review on newly diagnosed pediatric patients with type 2 diabetes mellitus to compare the effect of treatment regimen on body mass index (BMI) and hemoglobin A1c over a 6-month period.

METHODS

We conducted a retrospective chart review on patients with type 2 DM who presented to Nationwide Children's Hospital. Data were collected on therapy type, BMI, and hemoglobin A1c over a 6-month follow-up. Therapy type was divided into metformin, insulin, or combination insulin and metformin. 1,997 charts were reviewed for inclusion based on ICD-9 codes consistent with a diagnosis of diabetes, abnormal oral glucose tolerance test, or insulin resistance.

RESULTS

Of the 47 charts eligible for the review, 26 subjects were treated with metformin 1000-1500 mg daily, 14 patients were treated with insulin therapy, and 7 patients were treated with a combination of insulin and metformin therapy. At baseline, the only significant difference among groups was A1c (P = 0.012). In regression analysis with baseline A1c as a covariate, the only predictor of change in A1c over time was the A1c at onset (P < 0.001). Therapy type was not predictive of change (P = 0.905). Regression analysis showed a greater BMI at onset predicted a greater decrease in BMI (P = 0.006), but therapy type did not predict a change (P = 0.517).

CONCLUSION

Metformin may be as effective as insulin or combination therapy for treatment of diabetes from onset to 6-month follow-up.

Adiposity and β-cell function: relationships differ with ethnicity and age

The prevalence of type 2 diabetes is higher among African Americans (AA) vs. European Americans (EA), is highest at middle age, and is related to obesity. This study was conducted to test the hypothesis that the association of adiposity (percent body fat (%fat)) with indexes of insulin sensitivity (S(I)) and β-cell function would differ with ethnicity and age. Subjects were 168 healthy, normoglycemic AA and EA girls and women aged 7-12 years, 18-32 years, and 40-70 years. An intravenous glucose tolerance test (IVGTT) was used to assess indexes of insulin secretion and action: S(I), acute C-peptide secretion (X0); basal, first-phase, second-phase, and total β-cell responsivity to glucose (PhiB, Phi1, Phi2, and Phi(TOT), respectively); and the disposition index (DI = S(I) × Phi(TOT)). %Fat was assessed with dual energy X-ray absorptiometrys. Adiposity was significantly associated with S(I) among EA (-0.57, P < 0.001) but not AA (-0.20, P = 0.09). Adiposity appeared stimulatory to β-cell function in the two groups of younger subjects and in EA, but inhibitory in postmenopausal women, particularly AA postmenopausal women. Among AA postmenopausal women, %fat was inversely associated with Phi1 (r = -0.57, P < 0.05) and Phi(TOT) (r = -0.68, P < 0.01). These results suggest that the impact of adiposity on insulin secretion and action differs with age and ethnicity.

The role of European genetic admixture in the etiology of the insulin resistance syndrome in children: are the effects mediated by fat accumulation?

OBJECTIVES

To evaluate the contribution of European genetic admixture (EUADM) to insulin resistance syndrome (IRS) in a multiethnic sample of children age 7-12 years, and to explore whether body fat affects this relationship.

STUDY DESIGN

Anthropometric measurements and blood pressure were assessed in 243 children. After an overnight fast, an intravenous glucose tolerance test was conducted, and measures of fasting insulin/glucose, lipids, insulin sensitivity (SI), and acute insulin response to glucose (AIRg) were obtained. The proportion of EUADM was determined by maximum likelihood estimation using 140 ancestry informative markers. Subjects were stratified into tertiles according to the proportion of EUADM for analyses. Subjects were categorized as lean or obese using body fat percentage cutpoints (25% in boys, 30% in girls).

RESULTS

Among lean subjects (72%), the tertile representing the greatest proportion of EUADM was associated with higher SI (P<.001) and serum glucose (P<.05) and lower insulin (P<.05), AIRg (P<.001), high-density lipoprotein cholesterol (P=.05), and blood pressure (P<.05). However, among obese subjects, EUADM was associated only with SI (P<.05).

CONCLUSIONS

Our results suggest that population differences in IRS likely have a genetic component, but that the influence of genetic background may be masked by obesity.

Diabetes in sub-Saharan Africa

In Sub-Saharan Africa, prevalence and burden of type 2 diabetes are rising quickly. Rapid uncontrolled urbanisation and major changes in lifestyle could be driving this epidemic. The increase presents a substantial public health and socioeconomic burden in the face of scarce resources. Some types of diabetes arise at younger ages in African than in European populations. Ketosis-prone atypical diabetes is mostly recorded in people of African origin, but its epidemiology is not understood fully because data for pathogenesis and subtypes of diabetes in sub-Saharan African communities are scarce. The rate of undiagnosed diabetes is high in most countries of sub-Saharan Africa, and individuals who are unaware they have the disorder are at very high risk of chronic complications. Therefore, the rate of diabetes-related morbidity and mortality in this region could grow substantially. A multisectoral approach to diabetes control and care is vital for expansion of socioculturally appropriate diabetes programmes in sub-Saharan African countries.

Racial differences in the association between body fat distribution and lipid profiles among reproductive-age women

AIM

The aim of this study was to examine the racial and ethnic differences in the relationship between body fat distribution variables and serum lipid profiles.

METHODS

Secondary data analyses were conducted on 708 healthy women (204 blacks, 247 whites and 257 Hispanics), aged 16-33 years, seen in an outpatients clinic for contraception. Pearson correlation and multivariable linear regression techniques were used to identify racial/ethnic differences in the relationship between lipid profiles and body fat after adjusting for lean mass as well as demographic and lifestyle variables.

RESULTS

All body fat distribution variables were significantly associated with total cholesterol (TC) (r=0.14 to 0.26), triglycerides (TG) (r=0.13 to 0.46), HDL cholesterol (r=-0.13 to -0.34), cholesterol-to-HDL ratio (r=0.20 to 0.50) and atherogenic index of plasma (AIP) (r=0.16 to 0.49). Significant racial/ethnic differences were observed in many associations. After adjusting for lean mass, and other demographic and lifestyle factors, the study showed that black women demonstrated significantly weaker associations than their white and Hispanic counterparts using multivariable linear regression procedures.

CONCLUSION

The relationship between lipid profiles and body fat distribution variables varies by race/ethnicity in reproductive-age women. A better understanding of these racial/ethnic differences has important implications for clinical and public-health efforts in targeting the prevention of cardiovascular disease (CVD).

Racial differences in body fat distribution among reproductive-aged women

We examined the influence of race/ethnicity on body fat distribution for a given body mass index (BMI) among reproductive-aged women. Body weight, height, and body fat distribution were measured with a digital scale, wall-mounted stadiometer, and dual-energy x-ray absorptiometry, respectively, on 708 healthy black, white, and Hispanic women 16 to 33 years of age. Multiple linear regression was used to model the relationship between race/ethnicity and different body fat distribution variables after adjusting for BMI, age at menarche, and demographic and lifestyle variables. For a given BMI, white women had the highest total fat mass (FM(total)), trunk fat mass (FM(trunk)), and leg fat mass (FM(leg)), whereas Hispanic women had the highest percentage of FM(trunk) (%FM(trunk)) and trunk-to-limb fat mass ratio (FMR(trunk-to-limb)). Conversely, black women had the lowest FM(total), FM(trunk), percentage body fat mass (%FM), %FM(trunk), and FMR(trunk-to-limb), and the highest percentage of FM(leg). The %FM was similar in whites and Hispanics and lower in blacks. The race x BMI interactions were significant for almost all of the body fat distribution variables. Increasing in differences with increasing BMI were apparent between blacks and whites in FM(trunk), %FM(trunk), FMR(trunk-to-limb), %FM(leg), and %FM, and between blacks and Hispanics in FM(trunk), %FM(trunk), FMR(trunk-to-limb), and FM(leg). In summary, the distribution of body fat for a given BMI differs by race among reproductive-aged women. These findings raise questions regarding universally applied BMI-based guidelines for obesity and have implications for patient education regarding individual risk factors for cardiovascular disease and metabolic complications.

Obesity attenuates the contribution of African admixture to the insulin secretory profile in peripubertal children: a longitudinal analysis

The pubertal transition has been identified as a time of risk for development of type 2 diabetes, particularly among vulnerable groups, such as African Americans (AAs). Documented ethnic differences in insulin secretory dynamics may predispose overweight AA adolescents to risk for type 2 diabetes. The objectives of this longitudinal study were to quantify insulin secretion and clearance in a cohort of 90 AA and European American (EA) children over the pubertal transition and to explore the association of genetic factors and adiposity with repeated measures of insulin secretion and clearance during this critical period. Insulin sensitivity was determined by intravenous glucose tolerance test (IVGTT) and minimal modeling; insulin secretion and clearance by C-peptide modeling; genetic ancestry by admixture analysis. Mixed-model longitudinal analysis indicated that African genetic admixture (AfADM) was independently and positively associated with first-phase insulin secretion within the entire group (P < 0.001), and among lean children (P < 0.01). When examined within pubertal stage, this relationship became significant at Tanner stage 3. Total body fat was a significant determinant of first-phase insulin secretion overall and among obese children (P < 0.001). Total body fat, but not AfADM, was associated with insulin clearance (P < 0.001). In conclusion, genetic factors, as reflected in AfADM, may explain greater first-phase insulin secretion among peripubertal AA vs. EA; however, the influence of genetic factors is superseded by adiposity. The pubertal transition may affect the development of the beta-cell response to glucose in a manner that differs with ethnic/genetic background.

Indices of insulin action calculated from fasting glucose and insulin reflect hepatic, not peripheral, insulin sensitivity in African-American and Caucasian adolescents

Insulin stimulates muscle glucose uptake and inhibits hepatic glucose production. Measures of insulin sensitivity or insulin resistance must take both of these actions into account. Homeostatic model assessment of insulin resistance (HOMA(IR)) and quantitative insulin sensitivity check index (QUICKI) are two simple measures of insulin resistance and insulin sensitivity that are derived from fasting glucose and insulin levels as such it is likely that they reflect primary hepatic insulin action and not muscular effects. To prove this hypothesis, the relationships of HOMA(IR) and QUICKI to peripheral insulin sensitivity (S(I)(*)) and hepatic insulin resistance (HIR) were assessed in 34 adolescents (age 13.5 +/- 2.9 yr, body mass index 23.0 +/- 5.7, mean +/- SD; 16 Caucasian and 14 African-American). S(I)(*) and HIR were determined using the stable-labeled, frequently sampled intravenous glucose tolerance test (250 mg total glucose/kg, 13% [6,6]-D(2)-glucose). The former was calculated using the one-compartment minimal model and stable glucose concentration (S(I)(*)), and the latter was determined over the last hour of the study by multiplying hepatic glucose production (Steele's equation) by mean plasma insulin concentration. As expected, HOMA(IR) and QUICKI were significantly related to HIR (log HOMA(IR) and log HIR, r = 0.73, p < 0.001; QUICKI and log HIR, r = -0.69, p < 0.001) but not S(I)(*). When both S(I)(*) and HIR were included in the equations, only the relationships to log HIR were significant (log HOMA(IR), p < 0.001; QUICKI, p < 0.001). The relationships were similar in African-American and Caucasian subjects. These results demonstrate that in adolescents, HOMA(IR) and QUICKI assess hepatic but not peripheral insulin action.

Impaired endothelial function in healthy African-American adolescents compared with Caucasians

OBJECTIVE

To determine whether African-American adolescents have endothelial dysfunction compared with Caucasians and whether differences are a result of differences in insulin sensitivity calculated from total glucose (S(I)) or secretion.

STUDY DESIGN

Thirty-three Caucasian (13.6 +/- 2.6 years of age; body mass index [BMI] 21.6 +/- 4.4 kg/m2 mean +/- SD) and 25 African-American (13.3 +/- 2.9 years of age; BMI 24.0 +/- 4.4 kg/m2) adolescents were studied. Forearm blood flow (FBF; plethysmography) was measured before and after 5 minutes of arterial occlusion. S(I) and acute insulin response to glucose (AIRG) were measured using intravenous glucose tolerance tests and minimal modeling.

RESULTS

Baseline FBF did not differ between races. Postocclusion FBF was lower in African-Americans (17.2 +/- 1.2 vs 22.6 +/- 1.2 mL/dL/minute, P = .006). AIRG was higher in African-Americans (6050 +/- 940 vs 2410 +/- 30 microU minute/mL, P = .001). Pubertal stage had no effect. S(I) did not differ by race or pubertal stage. In African-Americans, percent fall in FVR following arterial occlusion correlated (r = 0.67, P = .001) with log AIRG. No relationships were found between percent fall in FVR and S(I) in either race.

CONCLUSION

African-American adolescents have decreased endothelial function. This may be a result of increased insulin secretion. Endothelial dysfunction in African-American adolescents may predispose to cardiovascular and type II diabetes.

Adiponectin is lower among African Americans and is independently related to insulin sensitivity in children and adolescents

Adiponectin is inversely related to adiposity and positively correlated with insulin sensitivity (S(i)). Sparse data exist on the contributions of ethnicity and body fat distribution to variance in serum adiponectin. Hypotheses tested were that adiponectin would be lower in African Americans compared with Caucasians; that adiponectin would be inversely related to central, not peripheral, fat; that adiponectin would be positively associated with S(i); and that baseline adiponectin would predict change in S(i) over 2 years in 150 African-American and Caucasian youth. Multiple linear regression modeling showed that adiponectin was lower in African-American versus Caucasian children (adjusted means 10.8 +/- 0.5 vs. 12.3 +/- 0.5 microg/ml, respectively; P < 0.05); inversely related to trunk fat (P < 0.05); and positively related to limb fat (P < 0.01). Addition of the acute insulin response to glucose to the model eliminated the significance of ethnicity. S(i), which was positively related to adiponectin (P < 0.05), was lower in African Americans (P < 0.001) and girls (P < 0.05). Baseline adiponectin did not predict change in S(i) over 2 years. In conclusion, adiponectin was positively correlated with S(i), inversely related to central fat, and positively related to peripheral fat. In addition, higher acute insulin response to glucose explained lower adiponectin among African-American children.

Validation of surrogate estimates of insulin sensitivity and insulin secretion in children and adolescents

OBJECTIVES

To compare insulin sensitivity and pancreatic beta-cell function measured by the euglycemic and the hyperglycemic clamp, with simple estimates of insulin sensitivity and pancreatic beta-cell function in youth. Study design We measured insulin sensitivity with a euglycemic clamp and first- and second-phase insulin secretion with a hyperglycemic clamp in 156 AA and white youths. Estimates of insulin sensitivity (fasting insulin level [I(F)], the ratio of fasting glucose [G(F)] to I(F) [G(F)/I(F)], homeostasis model assessment estimate of insulin sensitivity [HOMA IS], and quantitative insulin sensitivity check index [QUICKI]) and estimates of pancreatic beta-cell function (I(F), the ratio of I(F) to G(F) [I(F)/G(F)], and homeostasis model assessment estimate of pancreatic beta-cell function [HOMA %B]) were derived from fasting measurements.

RESULTS

In the total group, IS(Eu) correlated strongly with I(F) (r=-0.92), G(F)/I(F) (r=0.92), HOMA IS (r=0.91), and QUICKI (r=0.91) (P<.01). First-phase and second-phase insulin secretion correlated with I(F), I(F)/G(F), and HOMA %B (first-phase insulin secretion: r=0.76, 0.79, 0.82; second-phase insulin secretion: r=0.83, 0.86, 0.86, respectively; P<.01).

CONCLUSIONS

Simple estimates of insulin sensitivity and pancreatic beta-cell function using fasting insulin and glucose levels serve as surrogate measures of insulin sensitivity and secretion in nondiabetic youths. The validity of these conclusions in children with impaired glucose tolerance and type 2 diabetes mellitus remains to be determined.

Type 2 diabetes in childhood: the American perspective

The incidence of type 2 diabetes mellitus is steadily escalating throughout the world in people from a wide range of ethnic groups and all social and economic levels. Type 2 diabetes is no longer a disease only of adults: parallel with the global epidemic of type 2 diabetes in adults, an 'emerging epidemic' of type 2 diabetes has been observed in youth over the last decade. Research and clinical experience in adults have established that insulin resistance is a major risk factor for type 2 diabetes. However, insulin resistance alone is not sufficient to cause diabetes, which will develop only when insulin secretion by the beta-cells fails. This review discusses the recent emergence of type 2 diabetes in children and adolescents, its risk factors, pathophysiologic mechanisms and treatment modalities.

Metabolic effects of chronic glipizide gastrointestinal therapeutic system on serum glucose, insulin secretion, insulin sensitivity, and hepatic insulin extraction in glucose-tolerant, first-degree relatives of African American patients with type 2 diabetes: new insights on mechanisms of action

We examined the long-term metabolic effects of a potent sulfonylurea (SU), glipizide gastrointestinal therapeutic system (glipizide GITS) in normal glucose-tolerant (NGT), first-degree relatives of African American patients with type 2 diabetes in a randomized, placebo-controlled, double-blind manner for 24 months and 6 months after discontinuation of glipizide GITS. Fifty NGT African American first-degree relatives (n = 50)) were randomized to receive either glipizide GITS (GITS, 5 mg/d) or identical placebo (PLAC). The NGT consisted of NGT/GITS (n = 16; mean age, 43.1 +/- 8.7years; body mass index [BMI], 34.8 +/- 10) and NGT/PLAC (n = 34; 45.5 +/- 9.7 years; BMI, 31.3 +/- 3.1years). Each of the subjects underwent an oral glucose tolerance test (OGTT) and frequently sampled intravenous glucose tolerance test (FSIGT) at baseline and at yearly intervals for 2 years. Insulin sensitivity (Si) and glucose effectiveness (Sg) were determined by Bergman's minimal model method. Hepatic insulin extraction (HIE) was calculated as the molar ratio of C-peptide and insulin. The mean fasting serum glucose, insulin, and C-peptide levels in the NGT/GITS were not different from that of the NGT/PLAC. After oral glucose challenge, mean serum glucose responses slightly increased (P = not significant [NS]) at 12 and 24 months in the NGT/GITS group when compared with the baseline, 0 month, but remained unchanged in the NGT/PLAC group. In addition, serum insulin and C-peptide responses significantly increased in the NGT/GITS group, but were unchanged in the NGT/PLAC group at 12 and 24 months versus 0 month. The HIE, during OGTT, decreased by 30% from the baseline (0 month) values in the NGT/ GITS, but remained unchanged in the NGT/PLAC group at 12 and 24 months. Mean Si decreased by 30% from the baseline in the NGT/GITS group by 12 and 24 months, but remained unchanged in the NGT/PLAC group. However, the disposition index (DI) remained normal in the NGT/GITS and the NGT/PLAC groups. The DI data in the NGT/GITS group suggested that beta cells maintained the ability to compensate for the lower Si during the chronic GITS administration in our high risk African Americans. Chronic GITS was well tolerated without any symptoms of either hypoglycemia or weight gain in the NGT/IGTS group. After discontinuation of GITS, the altered metabolic parameters significantly improved, returning to baseline values in the NGT/IGTS group in 6 months. In summary, chronic glipizide GITS administration (5 mg/d) was associated with increased beta-cell secretion, peripheral hyperinsulinemia, reduced Si, and reduced HIE in glucose-tolerant, first-degree relatives of African American patients with type 2 diabetes. These metabolic changes were reversible within 6 months after discontinuation of glipizide GITS. Our study defines a unique mode of action of glipizide GITS in African Americans at high risk for type 2 diabetes. We conclude that the use of glipizide GITS in the primary prevention of type 2 diabetes in nondiabetic first-degree relatives of patients with type 2 diabetes impaired glucose homeostasis.

Differences in insulin secretion and sensitivity of Caucasian and African American prepubertal children

OBJECTIVE

To investigate whether differences in body composition of African American children (AA) and Caucasian children (C) explain differences in insulin sensitivity and secretion.

STUDY DESIGN

Prepubertal nondiabetic children (31 AA and 54 C) were studied; 84% were overweight. Participants underwent a 2-hour hyperglycemic clamp, to estimate insulin sensitivity (SI(clamp)) and secretion, and dual energy x-ray absorptiometry, to assess body composition.

RESULTS

AA had greater total body fat mass (P =.01), fasting, 1st phase, 2nd phase, and steady state insulin levels (P <.05). AA and C had similar glucose disposal rates, but AA had lower SI(clamp) (P <.05). Fasting, 1st phase, and steady state C-peptide were less in C (P <.05), whereas corresponding C-peptide/insulin ratios were higher (all P <.005). Insulin levels and SI(clamp) remained different in AA and C after adjustment for body fat or lean mass differences. Analyses restricted to only overweight AA and C showed similar trends.

CONCLUSION

Prepubertal African American children have higher baseline and glucose-stimulated insulin and C-peptide levels, as well as reduced insulin sensitivity that is not entirely explained by differences in adiposity. The lower C-peptide/insulin molar ratio in AA suggests that they probably have lower hepatic insulin clearance than Caucasian children.

Obesity intervention among African-American children and adolescents

Often, researchers and clinicians approach the African-American community from a deficit model with African Americans viewed as having less desirable health practices and higher disease risk; however, in developing interventions for African Americans, it is important to keep in mind positive aspects of black culture as they relate to obesity. For example, the cultural acceptance of a larger body type and less negative views toward overweight individuals need not be viewed as problematic or abnormal. In fact, it could be argued that majority culture has a dysfunctional view of body image and obesity. The fact that whites are less likely to be overweight than African Americans may stem from a value system that places undue emphasis on thinness, youth, and external beauty and a culture that imbues women with shame about how they look and what they eat. Thus, rather than holding whites and majority culture as the ideal, it may be important to incorporate the positive elements of black culture regarding body image and food rather than attempting to shift their values toward those of European Americans. How best to achieve a reduction in obesity and its medical consequences, without inducing undesirable shifts in body image and attitudes toward food, is a formidable but important challenge.