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

Relation of dietary insulin index and dietary insulin load to metabolic syndrome depending on the lifestyle factors: Tehran lipid and glucose study

AIM

The hypothesis of the effect of the insulinogenic effects of diet on the development of cardiovascular diseases has been proposed, but the findings of previous studies are very contradictory. We investigated the association between dietary insulin index (DII) and dietary insulin load (DIL), and metabolic syndrome (MetS) risk. Another objective was to examine the extent to which lifestyle (physical activity, smoking status, and weight change) and sex influence the relationship between DII, DIL, and MetS risk.

MATERIALS AND METHODS

We followed 1915 participants in the Tehran Lipid and Glucose Study. DIL and DII were calculated based on a validated food frequency questionnaire. Weight change was measured, and participants were categorized into > 3% weight loss, weight stable (± 3%), and > 3% weight gain. By joint classification, the association between DII and DIL (< median and ≥ median) and risk of MetS was assessed according to weight change, sex, physical activity levels, and smoking status. Cox proportional hazards models were used to estimate the HRs (95% CI), adjusting for potential confounders.

RESULTS

During 8.9 years of follow-up, among 1915 participants, we documented 591 new cases of MetS. DII and DIL were not associated with MetS risk in the crude and adjusted models. However, DIL and DII were associated with weight gain (≥ 3%). In the crude model, DIL and DII were associated with a higher risk of weight gain [HR: 1.74: 95% CI 1.50-2.03, and 1.70 (1.46-1.98), respectively]. These associations remained significant after further adjustment for confounders. The HRs were 1.61 (1.35-1.92) for DIL and 1.64 (1.39-1.93) for DII. Among men, women, participants with low physical activity levels, and smokers, the risk of MetS, independent of DIL and DII, only increased in a participant with weight gain. In women with weight stability, DIL and DII, higher than the median, were positively associated with MetS risk.

CONCLUSION

Our findings suggest that the association between MetS risk and a hyperinsulinemic diet depended on weight change.

Association between Healthy Lifestyle (Diet Quality, Physical Activity, Normal Body Weight) and Periodontal Diseases in Korean Adults

This study aimed to investigate the association between healthy lifestyle (HLS; i.e., diet quality, physical activity, normal weight) and periodontal diseases in Korean adults. Studying this association may help inform future intervention programs aimed at preventing the development of periodontal diseases. Raw data of the Korea National Health and Nutrition Examination Survey (KNHANES) VII (2016–2018) were used. Data from 12,689 adults aged 19 years and over who had a periodontal examination were analyzed. The associations between HLS and periodontal diseases were analyzed using multivariate logistic regression after adjusting for demographic and health factors as covariates. We found that each of the HLS (diet quality, physical activity, normal body weight) practices was significantly associated with periodontal diseases (OR: 1.32, 95% CI: 1.13–1.55; OR: 1.16, 95% CI: 1.04–1.30; OR: 1.26, 95% CI: 1.14–1.40, respectively). In particular, having poor HLS practices was identified as a risk factor for periodontal diseases (OR: 1.54, 95% CI: 1.10–2.15). HLS was associated with periodontal diseases. Thus, in addition to improving oral hygiene—the primary focus in the past—improving HLS should be emphasized for patients with periodontal diseases.

Racial differences in psychological stress and insulin sensitivity in non-Hispanic Black and White adolescents with overweight/obesity

INTRODUCTION

Racial differences in type 2 diabetes risk persist among non-Hispanic Black and non-Hispanic White adolescents with overweight/obesity; however, the role of psychological stress in this disparity is less clear.

PURPOSE

To examine racial differences in the association between psychological stress, insulin sensitivity (S_i), acute insulin response to glucose (AIR_g), and disposition index (DI) among non-Hispanic Black and non-Hispanic White adolescents with overweight/obesity.

METHODS

Ninety-six adolescents (60% female; 51% non-Hispanic Black; 16.6 ± 1.8 years of age) with overweight/obesity (BMI percentile ≥ 85th percentile) were included in this analysis. Psychological stress was assessed using the 14-item Perceived Stress Scale. Glucose and insulin data from an intravenous glucose tolerance test was modeled to obtain S_i, AIR_g, and DI. Multivariable linear regression models were used to examine the association between race, psychological stress and metabolic outcomes (S_i, AIR_g, and DI).

RESULTS

Race was a significant predictor of log-AIR_g and log-DI (ps < 0.05) independent of all covariates in the main effect models. Lower S_i (p_interaction = 0.014) and DI (p_interaction = 0.012) was also observed among Black adolescents who reported higher stress levels, whereas higher S_i and DI was observed among non-Hispanic White adolescents reporting higher stress in the race interaction models. Race however, did not moderate the association between psychological stress and AIR_g (p > 0.05), nor was stress associated with S_i, AIR_g, or DI ("p" "s" > 0.05) across all other models.

CONCLUSIONS

Psychological stress may play an important and distinct role in shaping racial differences in type 2 diabetes risk among adolescents with overweight/obesity. Additional research is needed to understand the long-term effects of psychological stress on metabolic health among non-Hispanic Black and non-Hispanic White adolescents with overweight/obesity.

Racial Differences in Cancer Susceptibility and Survival: More Than the Color of the Skin?

Epidemiological studies point to race as a determining factor in cancer susceptibility. In US registries recording cancer incidence and survival by race (distinguishing 'black versus white'), individuals of African ancestry have a globally increased risk of malignancies compared with Caucasians and Asian Americans. Differences in socioeconomic status and health-care access play a key role. However, the lesser disease susceptibility of Hispanic populations with comparable lifestyles and socioeconomic status as African Americans (Hispanic paradox) points to the concomitant importance of genetic determinants. Here, we overview the molecular basis of racial disparity in cancer susceptibility ranging from genetic polymorphisms and cancer-driver gene mutations to obesity, chronic inflammation, and immune responses. We discuss implications for race-adapted cancer screening programs and clinical trials to reduce disparities in cancer burden.

Racial/Ethnic Differences in Insulin Resistance and Beta Cell Function: Relationship to Racial Disparities in Type 2 Diabetes among African Americans versus Caucasians

Both biological and sociocultural factors have been implicated in the well-documented racial disparity in incidence and prevalence of type 2 diabetes (T2D) between African Americans (AA) and non-Hispanic whites (NHW). This review examines the extent to which biological differences in glucose metabolism, specifically insulin resistance and beta cell function (BCF), contribute to this disparity. The majority of available data suggests that AA are more insulin resistant and have upregulated BCF compared to NHW. Increasing evidence implicates high insulin secretion as a cause rather than consequence of T2D; therefore, upregulated BCF in AA may specifically confer increased risk of T2D in this cohort. Racial disparities in the metabolic characteristics of T2D have direct implications for the treatment and health consequences of this disease; therefore, future research is needed to determine whether strategies to reduce insulin secretion in AA may prevent or delay T2D and lessen racial health disparities.

Racial differences in peripheral insulin sensitivity and mitochondrial capacity in the absence of obesity

CONTEXT

African-American women (AAW) have an increased risk of developing type 2 diabetes compared with Caucasian women (CW). Lower insulin sensitivity has been reported in AAW, but the reasons for this racial difference and the contributions of liver versus skeletal muscle are incompletely understood.

OBJECTIVE

We tested the hypothesis that young, nonobese AAW manifest lower insulin sensitivity specific to skeletal muscle, not liver, and is accompanied by lower skeletal muscle mitochondrial oxidative capacity.

PARTICIPANTS AND MAIN OUTCOME MEASURES

Twenty-two nonobese (body mass index 22.7 ± 3.1 kg/m(2)) AAW and 22 matched CW (body mass index 22.7 ± 3.1 kg/m(2)) underwent characterization of body composition, objectively assessed habitual physical activity, and insulin sensitivity with euglycemic clamps and stable-isotope tracers. Skeletal muscle biopsies were performed for lipid content, fiber typing, and mitochondrial measurements.

RESULTS

Peripheral insulin sensitivity was 26% lower in AAW (P < .01), but hepatic insulin sensitivity was similar between groups. Physical activity levels were similar between groups. Lower insulin sensitivity in AAW was not explained by total or central adiposity. Skeletal muscle triglyceride content was similar, but mitochondrial content was lower in AAW. Mitochondrial respiration was 24% lower in AAW and correlated with skeletal muscle insulin sensitivity (r = 0.33, P < .05).

CONCLUSION

When compared with CW, AAW have similar hepatic insulin sensitivity but a muscle phenotype characterized by both lower insulin sensitivity and lower mitochondrial oxidative capacity. These observations occur in the absence of obesity and are not explained by physical activity. The only factor associated with lower insulin sensitivity in AAW was mitochondrial oxidative capacity. Because exercise training improves both mitochondrial capacity and insulin sensitivity, we suggest that it may be of particular benefit as a strategy for diabetes prevention in AAW.

Effectiveness of pre-school- and school-based interventions to impact weight-related behaviours in African American children and youth: a literature review

This review assessed the effectiveness of pre-school- and school-based obesity prevention and/or treatment interventions targeting healthy eating, physical activity or obesity in African American children and adolescents. Systematic searches were conducted for English-printed research articles published between January 1980 and March 2013. Retained articles included experimental studies conducted in the United States that targeted ≥ 80% African American/black children and adolescents and/or studies whose results were stratified by race/ethnicity, and that were conducted in pre-schools/head start or schools (excluding after-school programmes). Of the 12,270 articles identified, 17 met the inclusion criteria (pre-school, n=2; elementary school, n=7; middle and secondary schools, n=8). Thirteen studies found significant improvements in nutrition (pre-school, n=1; elementary, n=7; secondary, n=5) and three found significant improvements in physical activity (pre-school, n=1; elementary, n=2) variables of interest. Two studies (pre-school, n=1; secondary, n=1) reported significant reductions in obesity in African American children. The evidence available suggests school-based interventions are effective in promoting healthy nutrition behaviours in African American children. Conclusions overall and, particularly, about effects on physical activity and obesity are limited due to the small number of studies, differences in assessment approaches and a lack of follow-up assessments.

Insulin secretion and its association with physical activity, fitness and screen time in children

OBJECTIVES

To determine the independent associations of moderate to vigorous physical activity (MVPA), fitness, screen time, and adiposity with insulin secretion in children.

DESIGN AND METHODS

Caucasian youth (n = 423/630), 8-10 years old, with at least one obese biological parent, were studied (QUALITY cohort). Insulin secretion was measured using HOMA2-%B, area under the curve (AUC) of insulin to glucose over the first 30 minutes (AUC I/G(t30min)) of the OGTT and AUC I/G(t120min) over 2 hours. Fitness was measured by VO₂peak ; percent fat mass (PFM) by DXA; 7-day MVPA by accelerometry; self-reported screen time included television, video game, or computer use. Models were adjusted for age, sex, season, puberty, PFM, and insulin sensitivity [IS] (HOMA2-IS, Matsuda-ISI).

RESULTS

PFM was strongly associated with insulin secretion, even after adjustment for IS: for every 1% increase in PFM, insulin secretion increased from 0.3% to 0.8% across indices. MVPA was negatively associated with HOMA2-%B (P < 0.05), but not with OGTT-derived measures. Fitness was negatively associated with AUC I/G(t120min) (P < 0.05). Screen time showed a trend toward higher HOMA2-%B in girls (P = 0.060).

CONCLUSIONS

In children with an obese parent, lower insulin secretion is associated with lower adiposity, higher MVPA, better fitness, and possibly reduced screen time.

Physical activity and markers of insulin resistance in adolescents: role of cardiorespiratory fitness levels--the HELENA study

OBJECTIVE

To analyze the association between objectively assessed physical activity (PA) and markers of insulin resistance (IR) in European adolescents and to examine whether the association of objectively assessed PA and markers of IR is modified by cardiorespiratory fitness (CRF).

METHODS

A cross-sectional study at school setting was conducted in 1053 (554 girls) adolescents (12.5-17.5 yr). Weight, height, waist circumference, total body fat, PA (accelerometry), and CRF (20-m shuttle run test) were measured. Fasting insulin and glucose concentrations were measured, and homeostasis model assessment as well as quantitative insulin sensitivity check index were computed.

RESULTS

In males, vigorous PA (VPA) was negatively associated with markers of IR after adjusting for confounders including waist circumference (all p < 0.05). In females, moderate PA, moderate to vigorous PA, and average PA were negatively associated with markers of IR after adjusting for confounders (all p < 0.05). Moreover, when the sample was segmented by CRF levels all the PA intensities were significantly associated with the markers of IR in females with low CRF but not in those with middle-high CRF after adjusting for confounders.

CONCLUSIONS

The findings suggest that PA is negatively associated with markers of IR after adjusting for confounders including total and central body fat in both sexes, but this relationship is modified by the CRF levels being especially important in those females with low CRF. Preventive strategies should focus not only on increasing the volume of PA but also on enhancing CRF through VPA.

Childhood physical activity, sports and exercise and noncommunicable disease: a special focus on India

Establishing the relationship between childhood physical inactivity and noncommunicable disease (NCD) is difficult, since chronic disease and mortality are not direct health outcomes of physical inactivity in children. Published literature explores the relationship of physical inactivity with appearance of early childhood disease risk markers, the adverse impact of which may take some time to appear. Promoting childhood physical activity has multiple benefits including delay in evolution of risk factors contributing to adult degenerative disease. It is clear from available literature that physical inactivity or its surrogates constitute an important independent risk factor for NCD. This is likely to be underestimated not only because of measurement issues, but also because physical inactivity may act through other risk factors for NCD. To recognize and intervene on the issue of physical inactivity in children is important not only for the benefit of the child but in the context of NCD in later life. Studies on physical inactivity and its functional correlates are limited in India and this would be an important area for future research.

Use of MRI and CT for fat imaging in children and youth: what have we learned about obesity, fat distribution and metabolic disease risk?

Childhood obesity is a matter of great concern for public health. Efforts have been made to understand its impact on health through advanced imaging techniques. An increasing number of studies focus on fat distribution and its associations with metabolic risk, in interaction with genetics, environment and ethnicity, in children. The present review is a qualitative synthesis of the existing literature on visceral and subcutaneous abdominal, intrahepatic and intramuscular fat. Our search revealed 80 original articles. Abdominal as well as ectopic fat depots are prevalent already in childhood and contribute to abnormal metabolic parameters, starting early in life. Visceral, hepatic and intramuscular fat seem to be interrelated but their patterns as well as their independent contribution on metabolic risk are not clear. Some ethnic-specific characteristics are also prevalent. These results encourage further research in childhood obesity by using imaging techniques such as magnetic resonance imaging and computed tomography. These imaging methods can provide a better understanding of fat distribution and its relationships with metabolic risk, compared to less detailed fat and obesity assessment. However, studies on bigger samples and with a prospective character are warranted.

Physical activity is related to insulin sensitivity in children and adolescents, independent of adiposity: a review of the literature

In adults, there is evidence that physical activity effectively improves insulin sensitivity regardless of adiposity. Whether this is also the case in children and adolescents is less clear. Clarifying this matter may help to identify the best outcomes to target in exercise programs for these age groups, where changes in adiposity may not always be desirable or realistic. A review of the literature was conducted on studies that examined the relationships of physical activity, cardiorespiratory fitness and strength with insulin sensitivity independent of adiposity in children and adolescents. Experimental (intervention) and correlational (longitudinal and cross-sectional) studies on participants ages 18 years and younger were identified. A total of 42 studies were included in this review. Sample sizes in the studies ranged from 14 to 4955 participants, with individual ages ranging from 5 to 19 years. A significant relationship with insulin sensitivity existed in 78% of studies on physical activity, 69% of studies on cardiorespiratory fitness and 66% of studies on strength. In studies that examined both physical activity and cardiorespiratory fitness concurrently, evidence suggests that they are both correlated with insulin sensitivity independent of adiposity, especially when physical activity is at higher intensities. However, the strength of this relationship might be influenced by study design, measurement techniques and participant characteristics. This is the first review of its type to take research design into account and to examine study outcomes according to participant ethnicity, gender, age, pubertal status and weight status.

African ancestry and its correlation to type 2 diabetes in African Americans: a genetic admixture analysis in three U.S. population cohorts

The risk of type 2 diabetes is approximately 2-fold higher in African Americans than in European Americans even after adjusting for known environmental risk factors, including socioeconomic status (SES), suggesting that genetic factors may explain some of this population difference in disease risk. However, relatively few genetic studies have examined this hypothesis in a large sample of African Americans with and without diabetes. Therefore, we performed an admixture analysis using 2,189 ancestry-informative markers in 7,021 African Americans (2,373 with type 2 diabetes and 4,648 without) from the Atherosclerosis Risk in Communities Study, the Jackson Heart Study, and the Multiethnic Cohort to 1) determine the association of type 2 diabetes and its related quantitative traits with African ancestry controlling for measures of SES and 2) identify genetic loci for type 2 diabetes through a genome-wide admixture mapping scan. The median percentage of African ancestry of diabetic participants was slightly greater than that of non-diabetic participants (study-adjusted difference = 1.6%, P<0.001). The odds ratio for diabetes comparing participants in the highest vs. lowest tertile of African ancestry was 1.33 (95% confidence interval 1.13–1.55), after adjustment for age, sex, study, body mass index (BMI), and SES. Admixture scans identified two potential loci for diabetes at 12p13.31 (LOD = 4.0) and 13q14.3 (Z score = 4.5, P = 6.6×10⁻⁶). In conclusion, genetic ancestry has a significant association with type 2 diabetes above and beyond its association with non-genetic risk factors for type 2 diabetes in African Americans, but no single gene with a major effect is sufficient to explain a large portion of the observed population difference in risk of diabetes. There undoubtedly is a complex interplay among specific genetic loci and non-genetic factors, which may both be associated with overall admixture, leading to the observed ethnic differences in diabetes risk.

Independent benefits of meeting the 2008 physical activity guidelines to insulin resistance in obese latino children

We examined the independent association between moderate-to-vigorous physical activity (MVPA) and insulin resistance (IR) among obese Latino children (N = 113; 7-15 years) who were enrolled in a community-based obesity intervention. Baseline information on physical activity was gathered by self-report. Clinical assessments of body composition, resting energy expenditure (REE), as well as glucose and insulin responses to an oral glucose tolerance test (OGTT) were performed after an overnight fast. Insulin resistance was defined as a 2 h insulin concentration >57 μU·mL(-1). We observed that those obese children who met the 2008 Guidelines for MVPA (≥60 min/day) experienced a significantly lower odds of IR compared with those not meeting the Guidelines (OR = 0.29; 95% CI: (0.10-0.92)) and these findings were independent of age, sex, pubertal stage, acculturation, fasting insulin, and 2 h glucose concentrations. Efforts to promote 60 min or more of daily MVPA among children from ethnic minority and high-risk communities should assume primary public health importance.

A role for pancreatic beta-cell secretory hyperresponsiveness in catch-up growth hyperinsulinemia: Relevance to thrifty catch-up fat phenotype and risks for type 2 diabetes

Current notions about mechanisms by which catch-up growth predisposes to later type 2 diabetes center upon those that link hyperinsulinemia with an accelerated rate of fat deposition (catch-up fat). Using a rat model of semistarvation-refeeding in which catch-up fat is driven solely by elevated metabolic efficiency associated with hyperinsulinemia, we previously reported that insulin-stimulated glucose utilization is diminished in skeletal muscle but increased in white adipose tissue. Here, we investigated the possibility that hyperinsulinemia during catch-up fat can be contributed by changes in the secretory response of pancreatic beta-cells to glucose. Using the rat model of semistarvation-refeeding showing catch-up fat and hyperinsulinemia, we compared isocalorically refed and control groups for potential differences in pancreatic morphology and in glucose-stimulated insulin secretion during in situ pancreas perfusions as well as ex vivo isolated islet perifusions. Between refed and control animals, no differences were found in islet morphology, insulin content, and the secretory responses of perifused isolated islets upon glucose stimulation. By contrast, the rates of insulin secretion from in situ perfused pancreas showed that raising glucose from 2.8 to 16.7 mmol/l produced a much more pronounced increase in insulin release in refed than in control groups (p < 0.01). These results indicate a role for islet secretory hyperresponsiveness to glucose in the thrifty mechanisms that drive catch-up fat through glucose redistribution between skeletal muscle and adipose tissue. Such beta-cell hyperresponsiveness to glucose may be a key event in the link between catch-up growth, hyperinsulinemia and risks for later type 2 diabetes.

Physical activity as the main therapeutic tool for metabolic syndrome in childhood

Physical activity (PA) and diet directly influence obesity and metabolic syndrome (MS) as important determinants of body composition. Understanding how PA relates to MS in youth is of great importance, and could offer a common strategy for clinical and public health approaches to control this condition. The underlying disorder of MS is a condition of insulin resistance, and a strong relationship between PA level and insulin sensitivity is clearly ascertained. The type, duration, frequency and intensity of PA affect fuel metabolism, in particular carbohydrate and lipid oxidation. The possible modulation of metabolism because of increased fat oxidation by PA is the basis for both prevention and restoration of insulin resistance and MS in obese children. In daily clinical practice, diet followed by pharmacologic treatment are usually the approaches taken, whereas PA is often considered just a suggestion. Although diet and PA have different effects on body composition, with both contributing to fat loss, only PA increases muscle mass and thus has a direct effect on metabolic function, expressed by changes in cardiovascular risk factors. Therefore, it is important to remember their complementary but different targets in daily clinical practice, such as body weight control for diet and metabolic health for PA. In this review, we have summarized the literature on the relationship between PA and MS in pediatrics. Then, we have analyzed the possibility of using PA for MS treatment, as an alternative to drugs, by discussing the results of intervention studies, reasons for low compliance to PA, related benefits, adherence difficulties and costs. Finally, we have tried to suggest recommendations for a multiple-step PA strategy in children and adolescents at risk for MS, by considering PA as the 'key' player in treatment.

Diet quality and weight gain among black and white young adults: the Coronary Artery Risk Development in Young Adults (CARDIA) Study (1985-2005)

BACKGROUND

Little is known about the long-term health consequences of following the 2005 Dietary Guidelines for Americans (DGA; Washington, DC: US Government Printing Office, 2005).

OBJECTIVE

The objective was to examine the longitudinal association between diets consistent with the 2005 DGA and subsequent weight gain.

DESIGN

We used data from the Coronary Artery Risk Development in Young Adults (CARDIA) Study, a cohort of black and white men and women aged 18-30 y at baseline who attended ≤7 examinations from 1985-1986 to 2005-2006 (n = 4913). We created a 100-point Diet Quality Index (2005 DQI) to rate participants' diets based on meeting the 2005 DGA key recommendations. Longitudinal models of weight gain were adjusted for physical activity, smoking, energy intake, age, education, sex, and initial body mass index (BMI) and included interaction terms of DQI by race and initial BMI (if statistically significant).

RESULTS

We found effect modification by race (likelihood ratio test, P < 0.03 in all models). The mean adjusted 20-y weight change was +19.4 kg for blacks and +11.2 kg for whites with high diet quality (DQI >70) and +17.8 for blacks and +13.9 for whites with a DQI <50 (P < 0.05). In race-specific Cox models (with interaction terms for DQI × initial BMI, P < 0.05), a 10-point increase in DQI score was associated with a 10% lower risk of gaining 10 kg in whites with an initial BMI (in kg/m(2)) <25 but with a 15% higher risk in blacks with baseline obesity (P < 0.001).

CONCLUSIONS

Our findings do not support the hypothesis that a diet consistent with the 2005 DGA benefits long-term weight maintenance in American young adults. Greater need for attention to obesity prevention in future DGAs is warranted.

Population analysis of ethnicity and first-phase insulin release

OBJECTIVE

A mechanistic, physiologically-based pharmacokinetic (PK/PD) model was developed to describe the biphasic insulin release and evaluate the racial effects on the glucose-insulin kinetics in response to intravenous glucose.

METHODS

Fifteen African-American and 18 Caucasian children and adolescents between 8 and 18 years of age were enrolled in the study. Intravenous bolus of glucose (250 mg/kg) was administered and blood samples collected at frequent intervals for three hours following the glucose injection. A nonlinear mixed-effect population kinetic analysis with covariate structure was performed using Monolix.

RESULTS

A significantly higher initial insulin secretion from a readily releasable pool, which is responsible for the first-phase insulin secretion, was detected in African-Americans compared to Caucasians (p<0.05).

CONCLUSIONS

The proposed kinetic model is able to describe the glucose-stimulated insulin response, account for the first-phase insulin release and identify a racially-based pharmacokinetic difference in insulin's biphasic secretion behavior. It is hypothesized that the first-phase insulin component may play an important role in the development of type 2 diabetes. The proposed mechanistic model provides a quantitative analysis of the biphasic insulin release that may be useful in the early detection of diabetes.

Physical activity, obesity and cardiometabolic risk factors in 9- to 10-year-old UK children of white European, South Asian and black African-Caribbean origin: the Child Heart And health Study in England (CHASE)

AIMS/HYPOTHESIS

Physical inactivity is implicated in unfavourable patterns of obesity and cardiometabolic risk in childhood. However, few studies have quantified these associations using objective physical activity measurements in children from different ethnic groups. We examined these associations in UK children of South Asian, black African-Caribbean and white European origin.

METHODS

This was a cross-sectional study of 2,049 primary school children in three UK cities, who had standardised anthropometric measurements, provided fasting blood samples and wore activity monitors for up to 7 days. Data were analysed using multilevel linear regression and allowing for measurement error.

RESULTS

Overall physical activity levels showed strong inverse graded associations with adiposity markers (particularly sum of skinfold thicknesses), fasting insulin, HOMA insulin resistance, triacylglycerol and C-reactive protein; for an increase of 100 counts of physical activity per min of registered time, levels of these factors were 12.2% (95% CI 10.2-14.1%), 10.2% (95% CI 7.5-12.8%), 10.2% (95% CI 7.5-12.8%), 5.8% (95% CI 4.0-7.5%) and 19.2% (95% CI 13.9-24.2%) lower, respectively. Similar increments in physical activity levels were associated with lower diastolic blood pressure (1.0 mmHg, 95% CI 0.6-1.5 mmHg) and LDL-cholesterol (0.04 mmol/l, 95% CI 0.01-0.07 mmol/l), and higher HDL-cholesterol (0.02 mmol/l, 95% CI 0.01-0.04 mmol/l). Moreover, associations were broadly similar in strength in all ethnic groups. All associations between physical activity and cardiometabolic risk factors were reduced (albeit variably) after adjustment for adiposity.

CONCLUSIONS/INTERPRETATION

Objectively measured physical activity correlates at least as well with obesity and cardiometabolic risk factors in South Asian and African-Caribbean children as in white European children, suggesting that efforts to increase activity levels in such groups would have equally beneficial effects.

Tissue-specificity and ethnic diversity in obesity-related risk of cancer may be explained by variability in insulin response and insulin signaling pathways

Obesity is a predisposing risk factor for several chronic diseases. The link between obesity and cancer appears to be particularly complex. Notably only the risk for development of specific cancers appear to be affected. Moreover, the obesity-related risk of cancer is very different across ethnic groups. African-Americans appear particularly prone, whereas Hispanics appear to be relatively protected. Obesity is associated with increased levels of circulating insulin. These levels of elevated insulin may serve to promote proliferation of fat cells to accommodate the elevated nutrient flux. However, elevated levels of insulin may be a major mediating factor influencing cancer risk. This hypothesis alone cannot explain the complexity of the phenomenon. We suggest here that the different insulin responses to obesity of different ethnic groups may explain their different risk profiles. Moreover, we speculate that tissue-specific variations in the insulin signaling pathways may underlie their differential susceptibility to tumorigenesis in the face of elevated obesity. Elevated cancer risk may be an unwanted side effect of insulin responding to elevated nutrient flux in the obese which it serves to proliferate fat cells that provide a location for storage of ingested fat, which consequently prevents ectopic fat storage. Hence, while Hispanics may be protected from cancer risk in obesity because of their lower insulin response, they have an elevated risk of fatty liver disease. Reduction of insulin levels in obesity as a strategy to reduce cancer risk may pose additional problems unless it is combined also with interventions that aim to limit nutrient influx.

Differential influence of diet and physical activity on components of metabolic syndrome in a multiethnic sample of children

BACKGROUND

Treatment of the metabolic syndrome in adults is generally approached with diet and physical activity. The influence of diet and physical activity on cardiometabolic outcomes in children has not been clearly established.

OBJECTIVE

The main objective of this study was to test the hypothesis that the distribution of energy from fat and carbohydrate in addition to limited time spent engaging in physical activity would contribute to the prevalence of the metabolic syndrome and its components in a multiethnic pediatric population.

DESIGN

Observational, cross-sectional study. Diet was assessed by two 24-hour recalls, physical activity by accelerometry, body composition by dual-energy absorptiometry, and glucose and lipid levels using fasting sera.

MAIN OUTCOME MEASURES

Presence of metabolic syndrome and its components.

SUBJECTS

202 African-American (n=79), white (n=68), or Hispanic (n=55) healthy children aged 7 to 12 years.

STATISTICAL ANALYSIS

The contribution of diet and physical activity to the metabolic syndrome and its components were assessed by logistic regression and multiple linear regression analyses.

RESULTS

Prevalence of the metabolic syndrome in the total sample was 8.4%, with Hispanics more likely than whites and African Americans to meet the criteria. A greater intake of energy from carbohydrate was related to a greater waist circumference and higher concentrations of triglyceride and glucose particularly apparent within the African-American sample (P<0.05). Fat intake was associated with a lower waist circumference (P<0.05) and with lower concentrations of triglyceride (P<0.05) and glucose (P<0.001) in the total sample. Greater moderate/hard physical activity was associated with higher high-density lipoprotein cholesterol concentrations in whites (P<0.05). Increased sedentary behavior was related to greater glucose concentration in whites and Hispanics (P<0.05 for both).

CONCLUSIONS

Diet composition was more closely related to the components of the metabolic syndrome than was physical activity, with carbohydrate intake being adversely related to waist circumference, triglyceride levels, and glucose levels. Furthermore, relationships among diet and metabolic syndrome outcomes were stronger among African-American children, suggesting that nutrition interventions in this group may be particularly beneficial.

Physical fitness, activity, and insulin dynamics in early pubertal children

The objectives of this study were to identify the independent effect of physical activity and fitness on insulin dynamics in a cohort of European-, African-, and Hispanic-American children (n = 215) age 7-12 years and to determine if racial/ethnic in insulin dynamics could be statistically explained by racial/ethnic differences in physical activity or fitness. An intravenous glucose tolerance test and minimal modeling were used to derive the insulin sensitivity index (SI) and acute insulin response to glucose (AIRg). Fitness was assessed as VO2-170 and physical activity by accelerometer. Multiple regression models were tested for contributions of fitness and physical activity to SI and AIRg. Fitness was a stronger predictor of SI and AIRg than physical activity regardless of ethnicity; racial/ethnic differences in insulin dynamics were not accounted for by differences in fitness and/or physical activity.

Assessing the risk of impaired glucose metabolism in overweight adolescents in a clinical setting

OBJECTIVE

The study aims were to examine the relationship between adiposity and surrogate indices of pancreatic beta-cell function and insulin sensitivity obtained from an oral glucose tolerance test (OGTT) in overweight adolescents and determine which factors best predict impaired glucose metabolism (IGM).

METHODS

In a sample of adolescents (n=209) severity of overweight was determined by relative body mass index (RBMI). Insulin sensitivity (QUICKI, CISI) and beta-cell function (Fasting insulin: FI; Insulinogenic Index: deltaI30/deltaG30).

RESULTS

IGM was present in 26.8% (n=56), of which five had type 2 diabetes (T2DM). IGM prevalence was similar among RBMI strata. Once RBMI reached 150%, pronounced deterioration in CISI occurred (approximately 55%) (P<0.0001) while less dramatic reductions were seen in QUICKI (P<0.05), with fasting blood glucose (FBG) and beta-cell indices remaining stable. Compared to those with normal glucose tolerance, the IGM group exhibited higher beta-cell activity (FI, P<0.0001; deltaI30/deltaG30, P=0.004) with reduced insulin sensitivity (CISI, P<0.0001; QUICKI, P<0.0002). CISI was the single predictor of IGM (P<0.0001). Low insulin sensitivity increased adolescents' chance for IGM (CISI: OR=6.49, 95%CI=2.63, 16.05, P<0.0001; QUICKI: OR=3.16, 95%CI=1.61, 6.05, P=0.0006) as did beta-cell deterioration (deltaI30/delta G30: OR=3.18, 95%CI=1.33, 7.59, P=0.0069). Normal FBG occurred in 37.5% of youth with IGM.

CONCLUSION

The prevalence of IGM escalates in overweight adolescents, even at lower levels of overweight, and is associated with pronounced deterioration of insulin sensitivity. Current screening recommendations for FBG underestimate the prevalence of IGM in overweight adolescents thus limiting the opportunity for earlier intervention to prevent progression to diabetes.

Entero-insular axis and postprandial insulin differences in African American and European American children

BACKGROUND

African Americans have a greater insulin response after glucose challenge than do European Americans. Factors underlying this response are unknown.

OBJECTIVE

We determined the insulin, C-peptide, and incretin responses to a mixed macronutrient meal in African American and European American children. We hypothesized that 1) African Americans would have greater postprandial insulin and C-peptide responses, 2) African Americans would have higher incretin responses, and 3) the greater beta cell response among African Americans would be explained by greater incretin responses.

DESIGN

Subjects were 34 African American and 18 European American children. Glucose, insulin, C-peptide, glucagon-like peptide-1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP) were measured after the subjects consumed a liquid mixed meal. Insulin, C-peptide, and incretin responses were derived from the area under the curve (AUC) for minutes 0-30 (early response) and minutes 30-180 (late response) after meal ingestion.

RESULTS

The early insulin response was higher in African American (14,565 +/- 6840 pmol/L x 30 min) than in European American (7450 +/- 4077 pmol/L x 30 min; P < 0.01) children. Early C-peptide AUC did not differ by ethnicity (African Americans: 34.8 +/- 12.5; European Americans: 28.6 +/- 12.5 nmol/L x 30 min; P = 0.10). Early and late GLP-1 responses were lower in African Americans than in European Americans: 108.1 +/- 56.4 compared with 160.5 +/- 90.8 pmol/L x 30 min and 509.4 +/- 286.9 compared with 781.9 +/- 483.4 pmol/L x 150 min, respectively (P < 0.05 for both). The GIP response did not differ between groups.

CONCLUSIONS

The greater early insulin response in African Americans than in European Americans is not due to differences in circulating GLP-1 or GIP and may be due to lesser insulin clearance. Further research is needed to determine the physiologic implications of lower GLP-1 among African Americans.

Cardiorespiratory fitness and physical activity in youth with type 2 diabetes

OBJECTIVE

The increased incidence of type 2 diabetes (T2D) among youth is hypothesized to be due, in part, to low levels of fitness and activity. Therefore, the purpose of this investigation was to examine whether cardiorespiratory fitness and physical activity are reduced in youth with T2D compared with overweight controls.

PARTICIPANTS

Thirteen adolescent boys with previously diagnosed T2D (mean duration 2.4 +/- 1.8 yr) were matched for age and body mass index to 13 overweight, non-diabetic controls.

METHODS

Cardiorespiratory fitness was assessed during a progressive exercise test to volitional fatigue and physical activity was estimated from a 7-d physical activity recall.

RESULTS

Youth with T2D reported performing approximately 60% less moderate to vigorous physical activity compared with their non-diabetic counterparts (0.6 +/- 0.2 vs. 1.4 +/- 0.3 h/d, p = 0.04). Furthermore, diabetic youth exhibited significantly lower cardiorespiratory fitness levels compared with controls (28.7 +/- 1.6 vs. 34.6 +/- 2.2 mL/kg/min, p < 0.05).

CONCLUSIONS

These findings support the hypothesis that cardiorespiratory fitness and physical activity are reduced in youth with T2D. Whether reduced fitness and activity contributed to the pathophysiology of the disorder cannot be determined from the cross-sectional analysis. Longitudinal studies are warranted to examine whether improvements in fitness and increased physical activity can prevent the development of T2D in high-risk youth.

Relationships among fitness, body composition, and physical activity

PURPOSE

This study was designed to examine the associations of physical activity and body composition with cardiorespiratory fitness in eighth grade girls.

METHODS

A random sample of 1440 eighth grade girls at 36 schools participated in this cross-sectional investigation, which represented an ethnically and geographically diverse group. Cardiorespiratory fitness was assessed using a modified physical work capacity test on a cycle ergometer that predicted workload at a heart rate of 170 beats.min. Physical activity was assessed over 6 d in each girl using an accelerometer and body composition was estimated from body mass index and triceps skinfolds using a previously validated equation. Pearson correlations and multiple regression analyses were used to determine the relationships among fitness, physical activity, and body composition.

RESULTS

Significant linear relationships among cardiorespiratory fitness, body composition, and physical activity were found. The combination of fat and fat-free mass along with racial group and a race by fat-free-mass interaction accounted for 18% (R) of the variation in physical fitness. Adding moderate-to-vigorous physical activity to the regression model increased the R to 22%. Black girls had somewhat lower fitness levels (P < 0.05) especially at higher levels of fat and fat-free mass than other racial/ethnic groups.

CONCLUSIONS

Physical activity, fat-free mass, and the interaction between fat-free mass and racial group are significantly associated with cardiorespiratory fitness in adolescent girls.

Insulin resistance, physical fitness, body composition and leptin concentration in 7–8 year-old children

The aim of this study was to investigate the association between insulin resistance and physical fitness, leptin concentration, body composition and family history for diabetes in non-selected young children. Physical fitness, fasting plasma glucose, insulin and leptin concentrations, anthropometric characteristics and medical history were available in two hundred and fifty-seven 7-year-old Dutch children. Correlations with the homeostasis model assessment (HOMA) index for insulin resistance were studied. A multiple regression model was calculated for HOMA. The differences between children with or without a family history for diabetes were not significant. Boys scored higher on glucose concentration and aerobic fitness and lower on sum of skin folds and leptin concentration (p<.05). After adjustment for sum of skin folds, HOMA was significantly associated with leptin in both genders (boys r=.184 p=.031; girls r=.430 p=.000). The association between physical fitness and HOMA was mediated by sum of skin folds. The associations were stronger in girls than in boys. In the regression model (R(2)=.205) the leptin concentration was the only significant predictor for HOMA. The influence of family history for diabetes on insulin resistance is shown as a trend at this age. Our findings suggest that plasma leptin concentration is independently associated with the development of insulin resistance in a non-selected prepubertal population. The association of physical fitness with insulin resistance seems to be mediated by the sum of skin folds.

Racial disparity in glucagon-like peptide 1 and inflammation markers among severely obese adolescents

OBJECTIVE

Compared with Caucasians, obese African-American adolescents have a higher risk for type 2 diabetes. Subclinical inflammation and reduced glucagon-like peptide 1 (GLP-1) concentration are linked to the pathogenesis of the disease. We determined the relationship between insulin resistance, beta-cell activity, and subclinical inflammation with GLP-1 concentrations and whether racial disparities in GLP-1 response were present in 49 obese adolescents (14 +/- 3 years; 76% African American; 71% female).

RESEARCH DESIGN AND METHODS

Subjects underwent physical examination and an oral glucose tolerance test. We measured levels of high-sensitivity CRP (CRP(hs)), fibrinogen, glucose, GLP-1(total), GLP-1(active), and insulin. Insulin and glucose area under the curve (AUC), insulinogenic index (DeltaI30/DeltaG30), and composite insulin sensitivity index (CISI) were computed. Subjects were categorized by race and as inflammation positive (INF+) if CRP(hs) or fibrinogen were elevated.

RESULTS

No racial differences were seen in mean or relative BMI. Thirty-five percent of subjects had altered fasting or 2-h glucose levels (African American vs. Caucasian, NS), and 75% were INF+ (African American vs. Caucasian, P = 0.046). Glucose and insulin, CISI, and DeltaI30/DeltaG30 values were similar; African Americans had lower GLP-1(total) AUC (P = 0.01), GLP-1(active) at 15 min (P = 0.03), and GLP-1(active) AUC (P = 0.06) and higher fibrinogen (P = 0.01) and CRP(hs) (NS) compared with Caucasians.

CONCLUSIONS

African Americans exhibited lower GLP-1 concentrations and increased inflammatory response. Both mechanisms may act synergistically to enhance the predisposition of obese African Americans to type 2 diabetes. Our findings might be relevant to effective deployment of emerging GLP-1-based treatments across ethnicities.

Objectively measured time spent sedentary is associated with insulin resistance independent of overall and central body fat in 9- to 10-year-old Portuguese children

OBJECTIVE

We examined the independent relationships between objectively measured physical activity and insulin resistance in Portuguese children.

RESEARCH DESIGN AND METHODS

This is a school-based, cross-sectional study in 147 randomly selected girls (aged 9.8 +/- 0.3 years; 27.8 +/- 9.3% body fat) and 161 boys (aged 9.8 +/- 0.3 years; 22.0 +/- 9.2% body fat). Physical activity was assessed by the Actigraph accelerometer for 4 days and summarized as time spent sedentary (accelerometer counts <500/min), in light-intensity (accelerometer counts 500-2,000/min), and in moderate- and vigorous-intensity activity (accelerometer counts >2,001/min). We measured total and central fat mass by dual-energy X-ray absorptiometry. Insulin resistance was expressed as the homeostasis model assessment score.

RESULTS

Time (min/day) spent sedentary was significantly and positively associated with insulin resistance (beta-coefficient = 0.001 [95% CI 0.0002-0.002]; P = 0.013). Time spent in moderate- and vigorous-intensity physical activity (-0.002 [-0.003 to -0.001]; P = 0.0009) and overall physical activity (-0.001 [-0.008 to 0.003]; P < 0.0001) were significantly and inversely associated with insulin resistance. All associations remained statistically significant, although they were attenuated after further adjustments for sex, birth weight, sexual maturity, and total or central fat mass (P < 0.03).

CONCLUSIONS

Physical activity is associated with insulin resistance independent of total and central fat mass in children. Our results emphasize the importance of decreasing sedentary behavior and increasing time spent in moderate- and vigorous-intensity activity in children, which may have beneficial effects on metabolic risk factors regardless of the degree of adiposity.

Associations between physical activity, body fat, and insulin resistance (homeostasis model assessment) in adolescents: the European Youth Heart Study

BACKGROUND

More and better data are needed to understand the action of physical activity (PA) on insulin resistance and the concomitant relation with body fat in adolescence.

OBJECTIVE

We examined the relation between total PA and intensity levels with insulin resistance under special consideration of waist circumference and skinfold thickness.

DESIGN

This was a cross-sectional study of 613 adolescents (352 girls, 261 boys) with a mean (+/-SD) age of 15.5 +/- 0.5 y from Sweden and Estonia. Total, low, moderate, and vigorous PA was measured by accelerometry. Body fat estimators included waist circumference and the sum of 5 skinfold thicknesses. Fasting insulin and glucose were measured, and insulin resistance was calculated according to the homeostasis model assessment (HOMA). Linear regression analysis and analysis of covariance were used to determine the association between PA and insulin resistance while considering body fat. All estimates were adjusted for sex, country, pubertal status, and indicators of body fat when applicable.

RESULTS

Total, moderate, and vigorous PA were inversely correlated with HOMA. Body fat estimators were positively correlated with HOMA. Significant contrasts in HOMA concentrations were seen when comparing the lower 2 tertiles with the upper tertile of PA indicators. Repeating the analysis with body fat estimators showed significant contrasts in HOMA concentrations when comparing the lower tertiles with the upper tertile.

CONCLUSION

In view of an increase in obesity in young people, the results accentuate the role of PA in sustaining metabolic balance in adolescence and the potential benefit of an increase of time spent at higher PA levels for youth with relatively elevated amounts of body fat.

Exercise alone reduces insulin resistance in obese children independently of changes in body composition

CONTEXT

The number of obese children with insulin resistance and type 2 diabetes is increasing, but the best management strategy is not clear.

OBJECTIVE

The objective of this study was to assess the effect of a structured 8-wk exercise training program on insulin resistance and changes in body composition in obese children.

DESIGN

The study was 8 wk of structured supervised exercise intervention with outcome measures before and after the exercise period.

SUBJECTS

Fourteen obese children (12.70 +/- 2.32 yr; eight male, six female) with high fasting insulin levels were enrolled into the study.

INTERVENTION

INTERVENTION consisted of 8 wk of supervised circuit-based exercise training, composed of three fully supervised 1-h sessions per week.

OUTCOME MEASURES

Outcome measures were assessed pretraining program and posttraining program and included insulin sensitivity (euglycemic-hyperinsulinemic clamp studies), fasting insulin and glucose levels, body composition using dual energy x-ray absorptiometry scan, lipid profile, and liver function tests.

RESULTS

Insulin sensitivity improved significantly after 8 wk of training (M(lbm) 8.20 +/- 3.44 to 10.03 +/- 4.33 mg/kg.min, P < 0.05). Submaximal exercise heart rate responses were significantly lower following the training (P < 0.05), indicating an improvement in cardiorespiratory fitness. Dual energy x-ray absorptiometry scans revealed no differences in lean body mass or abdominal fat mass.

CONCLUSION

An 8-wk exercise training program increases insulin sensitivity in obese children, and this improvement occurred in the presence of increased cardiorespiratory fitness but is independent of measurable changes in body composition.

Independent associations of physical activity and cardiorespiratory fitness with metabolic risk factors in children: the European youth heart study

AIMS/HYPOTHESIS

High levels of cardiorespiratory fitness (CRF) and physical activity (PA) are associated with a favourable metabolic risk profile. However, there has been no thorough exploration of the independent contributions of cardiorespiratory fitness and subcomponents of activity (total PA, time spent sedentary, and time spent in light, moderate and vigorous intensity PA) to metabolic risk factors in children and the relative importance of these factors.

METHODS

We performed a population-based, cross-sectional study in 9- to 10- and 15- to 16-year-old boys and girls from three regions of Europe (n = 1709). We examined the independent associations of subcomponents of PA and CRF with metabolic risk factors (waist circumference, BP, fasting glucose, insulin, triacylglycerol and HDL-cholesterol levels). Clustered metabolic risk was expressed as a continuously distributed score calculated as the average of the standardised values of the six subcomponents.

RESULTS

CRF (standardised beta = -0.09, 95% CI -0.12, -0.06), total PA (standardised beta = -0.08, 95% CI -0.10, -0.05) and all other subcomponents of PA were significantly associated with clustered metabolic risk. After excluding waist circumference from the summary score and further adjustment for waist circumference as a confounding factor, the magnitude of the association between CRF and clustered metabolic risk was attenuated (standardised beta = -0.05, 95% CI -0.08, -0.02), whereas the association with total PA was unchanged (standardised beta = -0.08 95% CI -0.10, -0.05).

CONCLUSIONS/INTERPRETATION

PA and CRF are separately and independently associated with individual and clustered metabolic risk factors in children. The association between CRF and clustered risk is partly mediated or confounded by adiposity, whereas the association between activity and clustered risk is independent of adiposity. Our results suggest that fitness and activity affect metabolic risk through different pathways.

Fatness, fitness, and insulin sensitivity among 7- to 9-year-old children

OBJECTIVE

The purpose of this study was to examine the relationships among fatness and aerobic fitness on indices of insulin resistance and sensitivity in children.

RESEARCH DESIGN AND METHODS

A total of 375 children (193 girls and 182 boys) 7 to 9 years of age were categorized by weight as normal-weight, overweight, or obese and by aerobic fitness based on a submaximal physical working capacity test (PWC). Fasting blood glucose (GLU) and insulin (INS) were used to calculate various indices of insulin sensitivity (GLU/INS), the homeostasis model assessment (HOMA), and the quantitative insulin sensitivity check index (QUICKI). Surrogate measures of pancreatic beta cell function included the insulinogenic index (INS/GLU) and the HOMA estimate of pancreatic beta-cell function (HOMA %B).

RESULTS

Insulin sensitivity and secretion variables were significantly different between the normal-weight children and the overweight and obese subjects. Fasting insulin (FI), HOMA, QUICKI, and INS/GLU were significantly different between the overweight and obese subjects. Likewise, the high fitness group possessed a better insulin sensitivity profile. In general, the normal-weight-high fit group possessed the best insulin sensitivity profile and the obese-unfit group possessed the worst insulin sensitivity profile. Several significant differences existed among the six fat-fit groups. Of particular note are the differences within BMI groups by fitness level and the comparison of values between the normal-weight-unfit subjects and the overweight and obese subjects with high fitness.

CONCLUSIONS

The results indicate that aerobic fitness attenuates the difference in insulin sensitivity within BMI categories, thus emphasizing the role of fitness even among overweight and obese children.

Elevated total and central adiposity and low physical activity are associated with insulin resistance in children

The aim of this study was 2-fold: (1) to examine insulin resistance, blood lipid levels, and inflammatory markers in 9- to 11.5-year-old obese and lean children and (2) to identify factors that influence insulin resistance in this cohort of youths. Body mass index, skinfold thickness, waist circumference, physical activity (4-day triaxial accelerometer), cardiorespiratory fitness (submaximal bicycle ergometer test), and dietary intake (3-day food records) were evaluated in 27 obese and 27 lean boys and girls. Fasting blood samples were analyzed for insulin, glucose, lipids and lipoproteins, C-reactive protein (CRP), interleukin 6, soluble intercellular adhesion molecule, and soluble vascular cell adhesion molecule. Homeostasis model assessment (HOMA) was used to evaluate insulin resistance (HOMA-IR). Obese children presented higher HOMA-IR, CRP, and blood lipid levels (all P < .01) compared with lean children. Total body fat and waist circumference were positively associated with fasting insulin (r > or = 0.51), HOMA-IR (r > or = 0.56), CRP (r > or = 0.51), and blood triacylglycerol (r > or = 0.38), and were inversely correlated with high-density lipoprotein cholesterol (r > or = -0.39; all P < .01). Cardiorespiratory fitness was inversely associated with HOMA-IR (r = -0.24; P < .05), but this association disappeared when adjusted for age, sex, and fat mass. Waist circumference and total daily physical activity explained 49% of the variance in HOMA-IR in these children. In conclusion, these findings suggest that total and central adiposity are positively associated and physical activity is negatively associated with insulin resistance in children. Interventions to improve glucose metabolism in youth should target at reducing total body and abdominal fat and increasing physical activity. The lack of association between inflammatory markers and HOMA-IR suggests that obesity may precede the elevation of these markers in the evolution of insulin resistance in youth.

Socioeconomic disparities in insulin resistance: results from the Princeton School District Study

OBJECTIVES

The objectives of this study were to determine whether lower socioeconomic status (SES) is associated with changes in insulin resistance in adolescents over a 3-year period and explore moderators of this effect.

METHODS

A total of 1167 healthy non-Hispanic black and white participants in the Princeton School District Study, a longitudinal study of fifth to 12th graders in a suburban Midwestern public school district were included in this study. Inclusion criteria were a) physical examination and fasting morning blood draw at baseline and 3 years later, b) younger than 20 years old at follow up, and c) information available on SES provided by a parent. The influence of SES on insulin resistance and change in insulin resistance over time was examined using general linear models adjusting for multiple covariates. Models also assessed if race or baseline weight status changed the SES-insulin resistance relationship and explored the role of perceived stress.

RESULTS

Blacks and lower SES youth had higher body mass index z score and increased insulin resistance (p < .001). In multivariable models, lower parent education, but not household income, was associated with higher baseline insulin resistance (F = 7.84, p < .001) and worsening insulin resistance over time (F = 18.86, p < .001). Parent education's effect on change in insulin resistance was more pronounced for obese youth compared with nonobese (F interaction = 10.12, p < .001) even with adjustment for multiple covariates. Perceived stress did not alter these relationships.

CONCLUSIONS

Lower parent education appears to be related to increased insulin resistance both cross-sectionally and over time in black and white adolescents. Worsening insulin resistance is especially problematic for obese adolescents from families with low parent education.

Insulin resistance in children and adolescents

IR is hypothesized to be the important pathophysiologic link between adiposity and future development of type 2 diabetes and cardiovascular disease. A variety of methods for measuring IR have been validated in children, from the gold-standard hyperinsulinemic euglycemic clamp, to simple fasting measures based on fasting insulin and glucose levels. Studies have shown that there are a number of important risk factors for IR in children, including adiposity and visceral adiposity, race/ethnicity, puberty, a family history of type 2 diabetes, sex, and being small for gestational age or prematurity. However, obesity represents the critical risk factor for IR in children. Greater than 50% of obese adolescents in the US have IR. Formal assessment of IR in obese children may represent an important strategy for improving the efficacy of pharmacologic therapy for weight loss and chronic disease prevention.

Relationships of physical activity with metabolic syndrome features and low-grade inflammation in adolescents

AIMS/HYPOTHESIS

Physical activity has beneficial effects on symptoms of the metabolic syndrome and low-grade inflammation in adults. These associations have rarely been studied in adolescents. Moreover, it has not been established whether they depend on adiposity, fat localisation and adipokines.

SUBJECTS, MATERIALS AND METHODS

We used cross-sectional data of 640 12-year-old adolescents participating in the Intervention Centred on Adolescents' Physical Activity and Sedentary Behaviour Study (ICAPS). Weight, height, body fat mass and WHR were measured. Metabolic syndrome components, two inflammatory markers (IL-6 and C-reactive protein), plasma leptin, adiponectin and soluble TNF-alpha receptor 1 (sTNF-alpha R1) were determined. Insulin resistance was estimated by homeostasis model assessment (HOMA) and energy expenditure due to organised leisure-time physical activity (PAE) assessed by questionnaire.

RESULTS

The metabolic syndrome was present in 5.8% of the adolescents. After adjustment for sex, sexual maturity and socio-economic status, a beneficial relationship between PAE and all metabolic syndrome features was found, but only the associations with HOMA and IL-6 were independent of body fat mass and WHR. Adjusted means from the lowest to the highest tertile of PAE were 1.99, 1.80 and 1.78 for HOMA (p=0.04), and 0.88, 0.69 and 0.70 pg/ml for IL-6 (p=0.02). PAE was inversely associated with leptin, independently of body fat mass and WHR (p<10(-2)), but not with adiponectin or sTNF-alpha R1. Further adjustment for adipokines did not change the relationships of PAE with HOMA and IL-6.

CONCLUSIONS/INTERPRETATION

In adolescents, physical activity is inversely related to HOMA and IL-6, independently of adiposity and fat localisation. These relationships are not accounted for by adipokines.

Cardiovascular fitness and physical activity in children with and without impaired glucose tolerance

OBJECTIVE

To examine differences in cardiovascular fitness (VO(2max)) and physical activity levels in overweight Hispanic children with normal glucose tolerance (NGT) vs impaired glucose tolerance (IGT).

PARTICIPANTS

A total of 173 overweight (BMI percentile 97.0 +/- 3.1) Hispanic children ages 8-13 years with a family history of type 2 diabetes.

METHODS

VO(2max) was measured via a maximal effort treadmill test and open circuit spirometry. Physical activity was determined by questionnaire. Glucose tolerance was established by a 2-h oral glucose challenge (1.75 g of glucose/kg body weight). IGT was defined from an oral glucose tolerance test as a 2-h plasma glucose level > or =140 and <200 mg/dl.

RESULTS

IGT was detected in 46 of the 173 participants (approximately 27%); no cases of type 2 diabetes were identified. No significant differences were found between youth with NGT and those with IGT in absolute VO(2max) (2.2 +/- 0.6 vs 2.1 +/- 0.5 l/min), VO(2max) adjusted for gender, age, and body composition (2.2 +/- 0.2 vs 2.1 +/- 0.2 l/min), or recreational physical activity levels (8.7 +/- 8.2 vs 6.9 +/- 6.2 h/week).

CONCLUSION

Overweight Hispanic youth with IGT exhibit similar levels of VO(2max) and physical activity compared to their NGT counterparts. Longitudinal analyses are necessary to determine whether fitness/activity measures contribute significantly to diabetes risk over time in this group.

Physical activity, cardiovascular fitness, and insulin sensitivity among U.S. adolescents: the National Health and Nutrition Examination Survey, 1999-2002

OBJECTIVE

The purpose of this study was to examine the association of physical activity and cardiovascular fitness (CVF) with insulin sensitivity in a nationally representative sample of U.S. youth.

RESEARCH DESIGN AND METHODS

The study included 1,783 U.S. adolescents (11% Mexican American, 14% non-Hispanic black, 63% non-Hispanic white, and 12% other) aged 12-19 years who were examined in the 1999-2002 National Health and Nutrition Examination Survey. Physical activity was assessed by questionnaire and expressed in units of MET hours per week. Predicted maximal oxygen uptake (Vo(2max), expressed in milliliters per kilogram of body weight per minute), a measure of CVF, was determined by a submaximal multistage treadmill test. Insulin sensitivity was defined by the Quantitative Insulin Sensitivity Check Index.

RESULTS

Boys were more likely than girls to be highly active (>or=30 MET h/week; 51 vs. 37%, P < 0.001) and had higher levels of CVF (mean Vo(2max) 47 vs. 39 ml x kg(-1) x min(-1), P < 0.001). Sex-specific multiple regression models controlled for age, race/ethnicity, and BMI showed that in boys, high levels of physical activity and high levels of CVF were significantly and positively associated with insulin sensitivity (beta = 0.84, P < 0.001 and beta = 0.82, P = 0.01, respectively). Among girls, insulin sensitivity was not significantly associated with physical activity or with CVF but was inversely and significantly associated with BMI.

CONCLUSIONS

Increasing physical activity and CVF may have an independent effect of improving insulin sensitivity among boys. For girls, the primary role of physical activity may be in weight maintenance.

Efficacy of exercise for treating overweight in children and adolescents: a systematic review

BACKGROUND

Overweight prevalence among children/adolescents is increasing, while adult obesity may potentially cause a decline in life expectancy. More exercise is uniformly recommended, although treatment efficacy remains unclear.

OBJECTIVE

To determine the efficacy of exercise alone for treating overweight in children/adolescents.

DESIGN

A systematic review and meta-analysis of randomized trials published in English were completed following multiple database searches performed on December 10, 2004. Studies of isolated or adjunctive exercise/physical activity treatment in overweight/obese children or adolescents which reported any overweight outcome were included. Literature searches identified 645 papers which were manually searched, of which 45 were considered for inclusion, of which 13 papers which reported 14 studies were included (N=481 overweight boys and girls, aged approximately 12 years). Two reviewers independently identified relevant papers for potential inclusion and assessed methodological quality. Principal measures of effects included the mean difference (MD) (between treatment and control groups), the weighted MD (WMD), and the standardized MD (SMD).

RESULTS

Few studies were of robust design. The pooled SMD was -0.4 (-0.7, -0.1, P=0.006) for percent body fat, and -0.2 (-0.6, 0.1, P=0.07) for central obesity outcomes, whereas the pooled WMD was -2.7 kg (-6.1 kg, 0.8 kg, P=0.07) for body weight, all of which favored exercise. Pooled effects on body weight were significant and larger for studies of higher doses, whereas nonsignificant and smaller effects were seen for studies of lower doses of exercise (155-180 min/weeks vs 120-150 min/weeks).

CONCLUSIONS

Based on the small number of short-term randomized trials currently available, an aerobic exercise prescription of 155-180 min/weeks at moderate-to-high intensity is effective for reducing body fat in overweight children/adolescents, but effects on body weight and central obesity are inconclusive. Recommendations for future study designs are discussed.

Longitudinal changes in insulin sensitivity, insulin secretion, and beta-cell function during puberty

OBJECTIVE

To determine longitudinal changes in insulin sensitivity (SI), insulin secretion, and beta-cell function during puberty in white and black youth.

STUDY DESIGN

The tolbutamide-modified frequently sampled intravenous glucose tolerance test and minimal modeling were used to measure SI, the acute insulin response to glucose (AIRg), and beta-cell function (disposition index, DI) in white (n = 46) and black (n = 46) children (mean [+/-SD] age at baseline = 10.2 +/- 1.7 years). Growth curve models (including 272 observations) with SI, AIRg, and DI regressed on Tanner stage were run after adjusting for covariates.

RESULTS

After adjusting for covariates, growth curve models revealed that SI decreased and subsequently recovered by the end of puberty in whites and blacks (both p < .05), AIRg decreased linearly across Tanner stages in both races (both p < .001), and DI decreased across puberty in blacks (p = .001) but not in whites (p = .2).

CONCLUSIONS

White and black youth exhibited transient insulin resistance and diminished AIRg during puberty. The progressive decline in DI among blacks versus whites may reflect a unique effect of puberty on beta-cell compensation in blacks. Future studies are needed to identify whether this difference contributes to the increased risk of type II diabetes in young blacks.

Dietary fat intake and insulin resistance in black and white children

OBJECTIVE

The purpose of this study was to determine whether dietary fat intake above current Acceptable Macronutrient Distribution Range (AMDR) guidelines was associated with greater insulin resistance in black and white children.

RESEARCH METHODS AND PROCEDURES

We studied 142 healthy children (n = 81 whites, n = 61 blacks), 6.5 to 14 years old. Dietary composition was determined by repeated 24-hour dietary recall, body composition by DXA, visceral fat by computed tomography, and insulin sensitivity (SI) and acute insulin response to glucose (AIRg) by frequently sampled intravenous glucose tolerance test. Subjects were categorized by ethnicity (white/black) and dietary fat intake (above-AMDR/within-AMDR guidelines), and differences were analyzed by 2 x 2 analysis of covariance, adjusting for covariates.

RESULTS

After adjusting for total body fat, gender, and Tanner stage, subjects consuming dietary fat above AMDR intake guidelines had lower SI and higher AIRg. This effect was specific to black children (32% lower SI and 62% higher AIRg in above-AMDR compared with within-AMDR blacks) and was not seen in whites.

DISCUSSION

In black, but not white, children, those with dietary fat intake above current AMDR guidelines had lower SI and higher AIRg than those who met AMDR guidelines. These findings support current AMDR guidelines for dietary fat in black children and adolescents. The mechanism(s) underlying the ethnic differences in the relationship between dietary fat intake and SI in children require further investigation.

Increased physical activity reduces prevalence of periodontitis

OBJECTIVES

Physical activity has been shown to have a protective relationship with several chronic diseases. Recently, physical activity was also found to reduce the risk of periodontitis in a study in male health professionals. However, the relationship between physical activity and periodontitis in a diverse group of individuals is not thoroughly examined. The purpose of this study was to examine if there is an association between sustained physical activity and periodontitis in a subset of the third national health and nutrition examination survey (NHANES III).

METHODS

NHANES III participants 18 years of age or older who had had a periodontal examination and reported to have a similar physical activity (or inactivity) level for 10 years or longer were selected (n=2521). Multivariable logistic regression analysis was used to estimate the association between physical activity and periodontitis. The analysis was adjusted for: age, gender, race, education, smoking, body mass index, poverty index, vitamin use, healthy eating index, time since last dental visit, gingival bleeding, and dental calculus.

RESULTS

Engaging in the recommended level of physical activity was significantly associated with lower periodontitis prevalence (OR=0.58, 95% CI, 0.35-0.96). Smoking, however, was found to modify this relationship. The association was strong and significant among never (OR=0.46, 95% CI, 0.23-0.93) and former smokers (OR=0.26, 95% CI: 0.09-0.72), but not among current smokers (OR=1.10, 95% CI: 0.48-2.53).

CONCLUSIONS

These results suggest that engaging in the recommended level of exercise is associated with lower periodontitis prevalence, especially among never and former smokers.

Early ethnic difference in insulin-like growth factor-1 is associated with African genetic admixture

IGF-1 is a growth-promoting hormone. Numerous studies have reported higher systemic concentrations of IGF-1 among African Americans (AA) compared with European Americans (EA) before puberty. We conducted this cross-sectional analysis to determine whether African ancestral genetic background, dietary factors, energy expenditure, adiposity, and socioeconomic status contribute to this difference. Children were prepubertal, AA and EA males and females. Genetic admixture was assessed from approximately 20 ancestry informative genetic markers. Body composition was determined by dual-energy x-ray absorptiometry; intake of energy, carbohydrate, protein, and fat by 24-h dietary recall; activity-related energy expenditure by doubly labeled water and indirect calorimetry; and socioeconomic status (SES) according to the Hollingshead scale. IGF-1 and IGF binding protein-3 (IGFBP-3) were measured using immunoradiometric assays. AA children had significantly greater IGF-1 compared with EA children (p < 0.01). In addition, AA children had lower SES and greater protein intake relative to EAs (p < 0.05 for both). Multiple linear regression analysis revealed that the only significant independent predictors of IGF-1 were IGFBP-3 and African admixture (p < 0.01 for both). Thus, our data suggest that the greater IGF-1 of AA relative to EA children could have a genetic basis.