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

Associations Among Physical Activity, Adiposity, and Insulin Resistance in Children Exposed In Utero to Maternal Obesity With and Without Gestational Diabetes

PURPOSE

Investigate whether obesity risk and current weight status are independently associated with physical activity (PA) and whether PA is associated with adiposity and insulin resistance (homeostatic model assessment of insulin resistance) among children with high versus low obesity risk based on in utero exposure to maternal overweight/obesity with gestational diabetes mellitus (GDM; high risk) or without GDM (overweight/obesity; high risk) or maternal normal weight without GDM (low risk).

METHOD

Secondary analysis of data from children born to women with overweight/obesity and GDM, overweight/obesity without GDM, or normal weight without GDM. PA was assessed with accelerometry, percentage of body fat derived from anthropometrics, and homeostatic model assessment of insulin resistance calculated from glucose and insulin.

RESULTS

Among 4- to 10-year-old children (N = 163), analyses of covariance showed that children with a current BMI ≥85th percentile had less vigorous PA than those with BMI <85th percentile, but in utero exposure was not an independent predictor of PA. In linear regression modeling, moderate to vigorous PA was inversely associated with percentage of body fat and homeostatic model assessment of insulin resistance independent of age, Tanner stage, and accelerometer wear time, with stronger associations in high-risk groups.

CONCLUSIONS

Children's PA is related to current weight status but not underlying risk for obesity but may be especially important to reduce obesity and insulin resistance in high-risk children.

Higher n-6:n-3 Fatty Acid Intake Is Associated with Decreased Cardiometabolic Risk Factors in a Racially Diverse Sample of Children

BACKGROUND

Accumulating evidence implicates diet quality in childhood as playing a significant role in adult cardiometabolic health. Polyunsaturated fatty acids (PUFAs) of the n-6 (ω-6) and n-3 (ω-3) series contribute unique protective effects against cardiometabolic disease. As such, the ratio between n-6 and n-3 PUFAs is a dietary metric of interest in the early life span, although an optimum intake ratio has yet to be determined.

OBJECTIVE

This cross-sectional study assesses relations between the ratio of total n-6:n-3 PUFA intake and cardiometabolic risk factors in a racially diverse sample of children (n = 191) from the Admixture Mapping of Ethnic and Racial Insulin Complex Outcomes (AMERICO) study.

METHODS

Outcome measures included waist circumference, lipid concentrations, fasting glucose, and two 24-h dietary recalls from boys and girls aged 7-12 y who self-reported as European American (n = 81), African American (n = 55), or Hispanic American (n = 55). Linear regression analyses were used to assess associations between predictors of interest and outcomes after adjusting for covariates.

RESULTS

PUFA intake reflected in the n-6:n-3 ratio was inversely associated with concentrations of total and LDL cholesterol [β ± SE: -0.359 ± 0.107 (P = 0.001) and -0.189 ± 0.069 (P = 0.007), respectively]. Exploratory analyses showed that the intake of total n-6 PUFAs was not significantly predictive of any cardiometabolic risk factor assessed, whereas total n-3 PUFA intake was positively associated with concentrations of HDL cholesterol (β ± SE: 0.114 ± 0.042; P = 0.007).

CONCLUSIONS

Results suggest that the effect of n-6 and n-3 PUFA intake reflected in the ratio may be largely driven by n-3 PUFAs in reducing 2 lipid cardiometabolic risk factors among this multiethnic cohort of children. Until an ideal intake ratio is determined, nutritional counseling should focus on meeting recommended levels of both n-3 and n-6 PUFAs in order to establish beneficial childhood dietary patterns that may positively influence adult cardiometabolic health.

The health benefits of muscular fitness for children and adolescents: a systematic review and meta-analysis

BACKGROUND

Physical fitness during childhood and adolescence has been identified as an important determinant of current and future health status. While research has traditionally focused on the association between cardio-respiratory fitness and health outcomes, the association between muscular fitness (MF) and health status has recently received increased attention.

OBJECTIVE

The aim of this systematic review and meta-analysis was to evaluate the potential physiological and psychological benefits associated with MF among children and adolescents.

METHODS

A systematic search of six electronic databases (PubMed, SPORTDiscus, Scopus, EMBASE, PsycINFO and OVID MEDLINE) was performed on the 20th May, 2013. Cross-sectional, longitudinal and experimental studies that quantitatively examined the association between MF and potential health benefits among children and adolescents were included. The search yielded 110 eligible studies, encompassing six health outcomes (i.e., adiposity, bone health, cardiovascular disease [CVD] and metabolic risk factors, musculoskeletal pain, psychological health and cognitive ability). The percentage of studies reporting statistically significant associations between MF and the outcome of interest was used to determine the strength of the evidence for an association and additional coding was conducted to account for risk of bias. Meta-analyses were also performed to determine the pooled effect size if there were at least three studies providing standardised coefficients.

RESULTS

Strong evidence was found for an inverse association between MF and total and central adiposity, and CVD and metabolic risk factors. The pooled effect size for the relationship between MF and adiposity was r = -0.25 (95% CI -0.41 to -0.08). Strong evidence was also found for a positive association between MF and bone health and self-esteem. The pooled effect size for the relationship between MF and perceived sports competence was r = 0.39 (95% CI 0.34-0.45). The evidence for an association between MF and musculoskeletal pain and cognitive ability was inconsistent/uncertain. Where evidence of an association was found, the associations were generally low to moderate.

CONCLUSION

The findings of this review highlight the importance of developing MF in youth for a number of health-related benefits.

Use of a simple liquid meal test to evaluate insulin sensitivity and beta-cell function in children

Insulin sensitivity and β-cell function are useful indices of metabolic disease risk but are difficult to assess in young children because of the invasive nature of commonly used methodology. A meal-based method for assessing insulin sensitivity and β-cell function may at least partially alleviate concerns. The objectives of this study were to: (i) determine the association of insulin sensitivity assessed by liquid meal test with that determined by an insulin-modified frequently sampled intravenous glucose tolerance test (FSIGT); (ii) examine the association of insulin sensitivity derived from each test with measures of body composition, fat distribution and metabolic health (lipids, fasting insulin and glucose, and surrogate indices of insulin sensitivity); and (iii) examine the associations of indices of β-cell function derived from each test with total and regional adiposity. Forty-seven children (7-12 years) underwent both a liquid meal test and an FSIGT. The insulin sensitivity index derived from the meal test (SI-meal) was positively associated with that from the FSIGT (SI-FSIGT; r = 0.63; P < 0.001), and inversely with all measures of insulin secretion derived from the meal test. Both SI-meal and SI-FSIGT were associated with measures of total and regional adiposity. SI-meal, but not SI-FSIGT, was associated with triglycerides and fasting insulin, after adjusting for ethnicity, gender, pubertal stage and fat mass. Basal insulin secretion measured during the meal test was positively associated with all measures of adiposity, independent of insulin sensitivity. In conclusion, a liquid meal offers a valid and sensitive means of assessing insulin sensitivity and β-cell responsivity in young children.

Vitamin D and calcium-sensing receptor polymorphisms differentially associate with resting energy expenditure in peripubertal children

Given that calcium metabolism is influenced by genes and is tightly linked to energy-utilizing pathways, this study evaluated the association of single nucleotide polymorphisms (SNPs) in the vitamin D receptor (VDR) and calcium-sensing receptor (CASR) with resting energy expenditure (REE). In 273 boys and girls, 7-12 years of age, cross-sectional REE was measured via indirect calorimetry, body composition by DXA, and dietary measures by 24-h recall. SNPs for VDR Cdx-2 (rs11568820) and CASR A986S (rs1801725) were genotyped using the Illumina Golden Gate assay. Multiple linear regression models were used to determine the association between SNPs and REE. African American carriers of the 'A' VDR Cdx2 allele had increased levels of REE in the overall sample, and this association was apparent among participants with an adiposity level of <25 % and 30 % body fat in males and females, respectively. For CASR, an association between carriers of the 'A' allele and REE was observed only in those in the upper median of calcium intake. VDR and CASR variants are associated with REE in children and are influenced by levels of calcium intake and adiposity. Our results bring awareness to mechanisms underlying the regulation of REE and biological and dietary influential factors.

Objectively measured patterns of physical activity in primary school children in Coventry: the influence of ethnicity

AIMS

The aetiology of increased metabolic risk in South Asians is incompletely understood, but may include modifiable factors such as physical activity. This study assessed patterns of physical activity in UK primary school children and examined the influence of ethnicity.

METHODS

We studied a community sample of children aged 8-9 years attending primary schools in Coventry, UK. One hundred and sixty-one children wore combined physical activity and heart rate monitors for 7 days. Levels of activity and energy expenditure were compared between White European (n = 96) and South Asian children (n = 65). Patterns of physical activity during the school week were also described.

RESULTS

Seventy-three per cent of White Europeans compared with only 35% of South Asians achieved international recommendations of 60 minutes of moderate to vigorous physical activity daily (P < 0.0000). South Asians were less active during the week (106 ± 28 vs. 120 ± 32 counts/min, respectively, P = 0.0054) and at weekends (92 ± 34 vs. 108 ± 54 counts/min, P = 0.0118) compared with White Europeans. There were differences in energy expenditure with lower physical activity levels in South Asians (daily average 1.68 ± 0.13 vs. 1.76 ± 0.17, P < 0.0001). Differences were attributable to less activity after school in South Asians (97 ± 29 vs. 120 ± 43 counts/min, P < 0.0000) as daytime activity was comparable between groups (120 ± 41 vs. 124 ± 39 counts/min, P > 0.05).

CONCLUSION

South Asian children in Coventry do significantly less physical activity than White Europeans, mainly attributable to differences in after-school activity. Ethnically tailored interventions should explore whether physical activity can be increased in South Asian children and, if so, whether this increased physical activity improves metabolic health.

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.

Postprandial improvement in insulin sensitivity after a single exercise session in adolescents with low aerobic fitness and physical activity

The purpose of this study was to determine the acute and residual impact of a single exercise bout on meal glucose control in adolescents with habitually low physical activity. Twelve adolescents (seven females/five males, 14 ± 2 yr) completed three trials. One trial [No Exercise (No Ex)] was completed after refraining from vigorous activity for ≥ 3 d. On the other two trials, a 45-min aerobic exercise bout at 75% peak heart rate was performed either 17-h Prior Day Exercise (Prior Day Ex) trial or 1-h Same Day Exercise (Same Day Ex) trial before consuming the test meal (2803 kJ, 45/40/15% energy as carbohydrate/fat/protein, respectively). Compared to No Ex, insulin sensitivity (SI) (minimal model analysis) was increased by 45% (p < 0.03) and 78% (p < 0.01) on the Prior Day Ex and Same Day Ex trials, respectively. This improvement in glucose control was supported by corresponding reductions in the net area under the curve for glucose, insulin, and c-peptide, although there was no change in postprandial suppression of fatty acids. These results show that SI is improved with a single bout of moderate intensity exercise in adolescents with habitually low physical activity and that the residual beneficial effect of exercise lasts at least 17 h. This finding highlights the plasticity of exercise responses in youth and the importance of daily exercise for metabolic health.

The impact of ethnicity on objectively measured physical activity in children

Obesity and obesity-related diseases (cardiovascular disease/metabolic risk factors) are experienced differently in individuals from different ethnic backgrounds, which originate in childhood. Physical activity is a modifiable risk factor for obesity and related diseases. Both physical activity and metabolic risk factors track to adulthood, and thus understanding the physical activity patterns in children from different ethnic backgrounds is important. Given the limitations of self-report measures in children, this study provides a review of studies which have objectively measured physical activity patterns in children from different ethnic backgrounds. From a total of 16 studies, it can be concluded that physical activity does seem to vary amongst the ethnic groups especially South Asian and Black compared to White EU (European Union). The findings are less consistent for Hispanic/Mexican American children. However, there are several methodological limitations which need to be considered in future studies. Firstly, there is a need for consistency in the measurement of physical activity. Secondly, there are a range of complex factors such as socioeconomic status and body composition which affect both physical activity and ethnicity. Studies have failed to account for these differences limiting the ability to generalise that ethnicity is an independent risk factor for physical activity.

Getting to the height of the matter: the relationship between stature and adiposity in pre-pubertal children

OBJECTIVE

Height has been inversely associated with cardiometabolic disease, with adiposity as the proposed contributor. Childhood represents a time when underlying metabolic pathways converge to determine growth. Although the extent to which influence is relevant, insulin, as a key growth signaling factor, likely provides key insight into mechanisms linking height and adiposity. Insulin concentration displays well-established sex and racial differences, with hyperinsulinemia more common among African Americans (AA) females relative to European Americans (EA). The objective of our study was to evaluate the relationship between height and adiposity in children. In addition, a secondary objective was to evaluate potential moderation by insulin concentration.

DESIGN

Seventy-two pre-pubertal children aged 4-10 years (mu = 6.6 +/- .2) participated.

MAIN OUTCOME MEASURES

Percent fat was assessed by DXA and fasting insulin by serum assay.

RESULTS

Height was positively associated with percent fat in the overall sample (P = .04). When evaluated according to age, an association was identified at age seven years (P = .02). When evaluated by sex, a positive relationship was apparent only in AA girls (P = .05). Inclusion of insulin in the model attenuated all significant associations, barring marginal significance in those aged seven years (P = .08).

CONCLUSIONS

A positive relationship between height and adiposity is apparent, particularly among those in younger years, which is contrary to what has been consistently reported in adults. Interestingly, age seven years was identified as a point of race-associated divergence in body composition. The degree to which growth-related processes in childhood underlie developmental origins of health disparities warrants further study.

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.

A Hybrid Bayesian Network/Structural Equation (BN/SEM) Modeling Approach for Detecting Physiological Networks for Obesity-related Genetic Variants

GWAS studies have been successful in finding genetic determinants of obesity. To translate discovered genetic variants into new therapies or prevention strategies, molecular or physiological mechanisms need to be discovered. One strategy is to perform data mining of data sets with detailed phenotypic data, such as those present in dbGAP (database of Genotypes and Phenotypes) for hypothesis generation. We propose a novel technique that combines the power and computational efficiency of existing Bayesian Network (BN) learning algorithms with the statistical rigor of Structural Equation Modeling (SEM) to produce an overall system that searches the space of potential networks and evaluates promising candidates using standard SEM model selection criteria. We demonstrate our method using the analysis of a candidate SNP data set from the AMERICO sample, a multi-ethnic cross-sectional cohort of roughly three hundred children with detailed obesity-related phenotypes. We demonstrate our approach by showing genetic mechanisms for three obesity-related SNPs.

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.

The Effect of Exercise on Leptin, Insulin, Cortisol and Lipid Profiles in Obese Children

This prospective, randomized study investigated the effect of exercise on leptin, insulin, cortisol and lipid profiles in obese children. A total of 40 obese boys aged 10-12 years with a body mass index (BMI) ≥ 30 kg/m2 were randomly separated into an exercise group ( n = 20) that underwent a 12-week aerobic exercise programme and a non-exercise (control) group ( n = 20). The BMI, low-density lipoprotein, cortisol, leptin and insulin levels were significantly lower in the exercise group after 12 weeks compared with baseline values, whereas high-density lipoprotein levels were significantly higher. In contrast, in the control group, low-density lipoprotein, cortisol and leptin levels were significantly higher after 12 weeks compared with baseline values while high-density lipoprotein levels were significantly lower. These findings indicate the importance of regular exercise in the regulation of body weight and protection against cardiovascular risk factors in obese children.

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.