Alternative methods of insulin sensitivity assessment in obese children and adolescents

Urinary C-peptide and urinary C-peptide creatinine ratio as markers for insulin resistance in obese children and adolescents

BACKGROUND

Obesity is associated with insulin resistance (IR). Identifying high-risk obese children affected with IR is crucial to apply preventive management. We aimed to assess the diagnostic value of urinary C-peptide (UCP) and urinary C-peptide creatinine ratio (UCPCR) to diagnose IR in obese children.

METHODS

This prospective cross-sectional study was performed on 60 children with obesity as the study group. Sixty healthy children of matched age and sex with normal body mass index (BMI) served as the control group. Hemostasis model for the assessment of IR (HOMA-IR), glycated hemoglobin (HbA1c), fasting blood glucose and insulin, UCP, and UCPCR were assessed in all included children.

RESULTS

UCP and UCPCR were significantly higher in children with obesity (2.075 ± 0.783) ng/ml, (0.200 ± 0.021) nmol/mmol compared to the control group (1.012 ± 0.465) ng/ml, (0.148 ± 0.016) nmol/mmol, respectively. Both UCP and UCPCR were positively correlated with each other and with HOMA-IR, HbA1c, acanthosis nigricans, waist circumference, and BMI. At cutoff ≥2.45, the sensitivity of UCP to diagnose IR in obese children was 71.4%. At cutoff ≥0.20, the sensitivity of UCPCR to diagnose IR in obese children was 87.6%.

CONCLUSIONS

UCP and UCPCR are promising surrogate markers of IR in children and adolescents with obesity. However, UCPCR is a better marker than UCP.

IMPACT

Obesity is associated with IR. Identifying high-risk obese children affected with IR is crucial to apply preventive management. We aimed to assess the diagnostic value of UCP and UCPCR to detect IR in obese children. To the best of our knowledge, we are the first to use UCP and UCPCR to assess IR in obese children. We found that UCP and UCPCR are practical, easy, dependable noninvasive markers to assess IR in children with obesity and could potentially be useful in epidemiological studies and clinical practice.

A performance review of novel adiposity indices for assessing insulin resistance in a pediatric Latino population

INTRODUCTION

Body mass index (BMI) percentile or BMI adjusted for age and sex is the most common anthropometric index to monitor and assess obesity in children. However, the ability of BMI to accurately predict insulin resistance (IR) in youth is debated. Determining the best method to noninvasively measure IR in the pediatric population is especially important due to the growing prevalence of type 2 diabetes mellitus (T2DM), which is more likely to develop in people with IR. Therefore, this study analyzed the performance of BMI against newer anthropometric indices in assessing IR in a pediatric Latino identifying sample.

METHODS

We studied 127 pediatric Latino participants from the Arizona Insulin Resistance (AIR) registry and performed linear regression analyses between various measures of IR and adiposity indices, including body mass index (BMI), triponderal mass index (TMI), body adiposity index (BAI), pediatric body adiposity index (pBAI), a body shape index (ABSI), abdominal volume index (AVI), waist to height ratio (WtHR) and waist to hip ratio (WHR). Log transformations of each index adjusted for age and sex and IR were used for the linear regressions. Additionally, we generated receiver operating characteristics (ROC) from logistic regressions between HOMA-IR and HOMA2IR against the same indices.

RESULTS

Using the homeostatic assessment of insulin resistance (HOMA-IR), HOMA2IR, the quantitative insulin-sensitivity check index (QUICKI), fasting serum insulin, and FPG/FSI to measure IR, we showed that BMI adjusted for age and sex performs similarly to many of the newer indices in our sample. The correlation coefficients for pBAI [R2: 0.27, 95% confidence interval: 0.88-1.81, p < 0.001] and BMI [R2: 0.27, 95% confidence interval: 0.92-1.92, p < 0.001] were the highest for HOMA-IR. Similarly, pBAI [R2: 0.29, 95% confidence interval: 0.88-1.72, p < 0.001] and BMI [R2: 0.29, 95% confidence interval: 0.93-1.83, p < 0.001] were the highest for HOMA2IR. A similar trend was observed with QUICKI, FSI, and FPG/FSI. ABSI had the lowest R ² value for all measures of IR. Area under the curve (AUC) values for the receiver operating characteristics (ROC) for HOMA-IR and HOMA2IR support these conclusions.

CONCLUSIONS

BMI adjusted for age and sex, despite its usage and simplicity, still stacks up well against newer indices in our Latino sample. Testing these indices across larger samples is necessary to generalize these findings and translate performance to adults.

Difference in Insulin Resistance Assessment between European Union and Non-European Union Obesity Treatment Centers (ESPE Obesity Working Group Insulin Resistance Project)

INTRODUCTION

The obesity epidemic has become one of the most important public health issues of modern times. Impaired insulin sensitivity seems to be the cornerstone of multiple obesity related comorbidities. However, there is no accepted definition of impaired insulin sensitivity.

OBJECTIVE

We hypothesize that assessment of insulin resistance differs between centers.

METHODS

The ESPE Obesity Working Group (ESPE ObWG) Scientific Committee developed a questionnaire with a focus on the routine practices of assessment of hyperinsulinemia and insulin resistance, which was distributed through Google Docs platform to the clinicians and researchers from the current ESPE ObWG database (n = 73). Sixty-one complete responses (84% response rate) from clinicians and researchers were analyzed: 32 from European Union (EU) centers (representatives of 14 countries) and 29 from Non-EU centers (representatives from 10 countries). Standard statistics were used for the data analysis.

RESULTS

The majority of respondents considered insulin resistance (IR) as a clinical tool (85.2%) rather than a research instrument. For the purpose of IR assessment EU specialists prefer analysis of the oral glucose tolerance test (OGTT) results, whereas non-EU ones mainly use Homeostatic Model Assessment of Insulin Resistance (HOMA-IR; p = 0.032). There was no exact cutoff for the HOMA-IR in either EU or non-EU centers. A variety of OGTT time points and substances measured per local protocol were reported. Clinicians normally analyzed blood glucose (88.52% of centers) and insulin (67.21%, mainly in EU centers, p = 0.0051). Furthermore, most participants (70.5%) considered OGTT insulin levels as a more sensitive parameter of IR than glucose. Meanwhile, approximately two-thirds (63.9%) of the centers did not use any cutoffs for the insulin response to the glucose load.

CONCLUSIONS

Since there is no standard for the IR evaluation and uniform accepted indication of performing, an OGTT the assessment of insulin sensitivity varies between EU and non-EU centers. A widely accepted standardized protocol is needed to allow comparison between centers.

Genetic Risk Score for Type 2 Diabetes and Traits Related to Glucose-Insulin Homeostasis in Youth: The Exploring Perinatal Outcomes Among Children (EPOCH) Study

OBJECTIVE

The metabolic phenotype of youth-onset type 2 diabetes (T2D) differs from that of adult-onset T2D, but little is known about genetic contributions. We aimed to evaluate the association between a T2D genetic risk score (GRS) and traits related to glucose-insulin homeostasis among healthy youth.

RESEARCH DESIGN AND METHODS

We used data from 356 youth (mean age 16.7 years; 50% female) in the Exploring Perinatal Outcomes Among Children (EPOCH) cohort to calculate a standardized weighted GRS based on 271 single nucleotide polymorphisms associated with T2D in adults. We used linear regression to assess associations of the GRS with log-transformed fasting glucose, 2-h glucose, HOMA of insulin resistance (HOMA-IR), oral disposition index, and insulinogenic index adjusted for age, sex, BMI z score, in utero exposure to maternal diabetes, and genetic principal components. We also evaluated effect modification by BMI z score, in utero exposure to maternal diabetes, and ethnicity.

RESULTS

Higher weighted GRS was associated with lower oral disposition index (β = -0.11; 95% CI -0.19, -0.02) and insulinogenic index (β = -0.08; 95% CI -0.17, -0.001), but not with fasting glucose (β = 0.01; 95% CI -0.01, 0.02), 2-h glucose (β = 0.03; 95% CI -0.0004, 0.06), or HOMA-IR (β = 0.02; 95% CI -0.04, 0.07). BMI z score and in utero exposure to maternal diabetes increased the effect of the GRS on glucose levels.

CONCLUSIONS

Our results suggest that T2D genetic risk factors established in adults are relevant to glucose-insulin homeostasis in youth and that maintaining a healthy weight may be particularly important for youth with high genetic risk of T2D.

Targeting skeletal muscle mitochondria to prevent type 2 diabetes in youth

The prevalence of type 2 diabetes (T2D) has increased dramatically over the past two decades, not only among adults but also among adolescents. T2D is a systemic disorder affecting every organ system and is especially damaging to the cardiovascular system, predisposing individuals to severe cardiac and vascular complications. The precise mechanisms that cause T2D are an area of active research. Most current theories suggest that the process begins with peripheral insulin resistance that precedes failure of the pancreatic β-cells to secrete sufficient insulin to maintain normoglycemia. A growing body of literature has highlighted multiple aspects of mitochondrial function, including oxidative phosphorylation, lipid homeostasis, and mitochondrial quality control in the regulation of peripheral insulin sensitivity. Whether the cellular mechanisms of insulin resistance in adults are comparable to that in adolescents remains unclear. This review will summarize both clinical and basic studies that shed light on how alterations in skeletal muscle mitochondrial function contribute to whole body insulin resistance and will discuss the evidence supporting high-intensity exercise training as a therapy to circumvent skeletal muscle mitochondrial dysfunction to restore insulin sensitivity in both adults and adolescents.

Systematic review to identify and appraise outcome measures used to evaluate childhood obesity treatment interventions (CoOR): evidence of purpose, application, validity, reliability and sensitivity

BACKGROUND

Lack of uniformity in outcome measures used in evaluations of childhood obesity treatment interventions can impede the ability to assess effectiveness and limits comparisons across trials.

OBJECTIVE

To identify and appraise outcome measures to produce a framework of recommended measures for use in evaluations of childhood obesity treatment interventions.

DATA SOURCES

Eleven electronic databases were searched between August and December 2011, including MEDLINE; MEDLINE In-Process and Other Non-Indexed Citations; EMBASE; PsycINFO; Health Management Information Consortium (HMIC); Allied and Complementary Medicine Database (AMED); Global Health, Maternity and Infant Care (all Ovid); Cumulative Index to Nursing and Allied Health Literature (CINAHL) (EBSCOhost); Science Citation Index (SCI) [Web of Science (WoS)]; and The Cochrane Library (Wiley) - from the date of inception, with no language restrictions. This was supported by review of relevant grey literature and trial databases.

REVIEW METHODS

Two searches were conducted to identify (1) outcome measures and corresponding citations used in published childhood obesity treatment evaluations and (2) manuscripts describing the development and/or evaluation of the outcome measures used in the childhood intervention obesity evaluations. Search 1 search strategy (review of trials) was modelled on elements of a review by Luttikhuis et al. (Oude Luttikhuis H, Baur L, Jansen H, Shrewsbury VA, O'Malley C, Stolk RP, et al. Interventions for treating obesity in children. Cochrane Database Syst Rev 2009;1:CD001872). Search 2 strategy (methodology papers) was built on Terwee et al.'s search filter (Terwee CB, Jansma EP, Riphagen II, de Vet HCW. Development of a methodological PubMed search filter for finding studies on measurement properties of measurement instruments. Qual Life Res 2009;18:1115-23). Eligible papers were appraised for quality initially by the internal project team. This was followed by an external appraisal by expert collaborators in order to agree which outcome measures should be recommended for the Childhood obesity Outcomes Review (CoOR) outcome measures framework.

RESULTS

Three hundred and seventy-nine manuscripts describing 180 outcome measures met eligibility criteria. Appraisal of these resulted in the recommendation of 36 measures for the CoOR outcome measures framework. Recommended primary outcome measures were body mass index (BMI) and dual-energy X-ray absorptiometry (DXA). Experts did not advocate any self-reported measures where objective measurement was possible (e.g. physical activity). Physiological outcomes hold potential to be primary outcomes, as they are indicators of cardiovascular health, but without evidence of what constitutes a minimally importance difference they have remained as secondary outcomes (although the corresponding lack of evidence for BMI and DXA is acknowledged). No preference-based quality-of-life measures were identified that would enable economic evaluation via calculation of quality-adjusted life-years. Few measures reported evaluating responsiveness.

LIMITATIONS

Proposed recommended measures are fit for use as outcome measures within studies that evaluate childhood obesity treatment evaluations specifically. These may or may not be suitable for other study designs, and some excluded measures may be more suitable in other study designs.

CONCLUSIONS

The CoOR outcome measures framework provides clear guidance of recommended primary and secondary outcome measures. This will enhance comparability between treatment evaluations and ensure that appropriate measures are being used. Where possible, future work should focus on modification and evaluation of existing measures rather than development of tools de nova. In addition, it is recommended that a similar outcome measures framework is produced to support evaluation of adult obesity programmes.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Framework of outcome measures recommended for use in the evaluation of childhood obesity treatment interventions: the CoOR framework

INTRODUCTION

Consensus is lacking in determining appropriate outcome measures for assessment of childhood obesity treatments. Inconsistency in the use and reporting of such measures impedes comparisons between treatments and limits consideration of effectiveness. This study aimed to produce a framework of recommended outcome measures: the Childhood obesity treatment evaluation Outcomes Review (CoOR) framework.

METHODS

A systematic review including two searches was conducted to identify (1) existing trial outcome measures and (2) manuscripts describing development/evaluation of outcome measures. Outcomes included anthropometry, diet, eating behaviours, physical activity, sedentary time/behaviour, fitness, physiology, environment, psychological well-being and health-related quality of life. Eligible measures were appraised by the internal team using a system developed from international guidelines, followed by appraisal from national external expert collaborators.

RESULTS

A total of 25,486 papers were identified through both searches. Eligible search 1 trial papers cited 417 additional papers linked to outcome measures, of which 56 were eligible. A further 297 outcome development/evaluation papers met eligibility criteria from search 2. Combined, these described 191 outcome measures. After internal and external appraisal, 52 measures across 10 outcomes were recommended for inclusion in the CoOR framework.

CONCLUSION

Application of the CoOR framework will ensure greater consistency in choosing robust outcome measures that are appropriate to population characteristics.

Blood sugar levels are higher in obese young children in Sweden than in Poland

AIM

An elevated fasting glucose level is an early sign of metabolic dysfunction in obese children. This study compared fasting glucose levels in obese young children in Poland and Sweden.

METHODS

We identified 109 obese children aged between two and 10 years from a Polish obesity register, with a mean BMI SDS (SD) of 3.72 (0.86). Each Polish child was matched by gender, age and degree of obesity, with ten children (n = 1090) from BORIS, the Swedish national childhood obesity treatment register. A group of 86 Swedish nonobese children served as controls.

RESULTS

The mean fasting glucose values of the Polish, Swedish and nonobese cohorts were 4.73 (0.51) mmol/L, 4.92 (0.50) mmol/L and 4.56 (0.39) mmol/L, respectively. After adjusting for variables affecting fasting glucose, the mean glucose value of the Swedish obese children was 0.20 mmol/L higher than that of Polish obese children (p < 0.0001) and 0.41 mmol/L higher than in nonobese controls (p < 0.0001).

CONCLUSION

Swedish obese young children had higher glucose levels than Polish obese young children. This suggests that Swedish obese children face a higher risk of the prediabetic stage impaired fasting glycaemia.

Estimation of insulin sensitivity in children: methods, measures and controversies

Insulin resistance is defined as a state where insulin produces a diminished biological response, primarily in its capacity as a glucose-regulating hormone. Insulin resistance is commonly diagnosed by pediatric clinicians, but is rarely measured directly in children or adolescents. This review provides an overview of the techniques that can be used to assess insulin sensitivity in children, summarizing the methods involved, the assumptions, pitfalls, and appropriate uses of each technique, as well as their validation and reproducibility in pediatric samples.

Adenovirus-36 is associated with obesity in children and adults in Sweden as determined by rapid ELISA

BACKGROUND

Experimental and natural human adenovirus-36 (Adv36) infection of multiple animal species results in obesity through increasing adipogenesis and lipid accumulation in adipocytes. Presence of Adv36 antibodies detected by serum neutralization assay has previously been associated with obesity in children and adults living in the USA, South Korea and Italy, whereas no association with adult obesity was detected in Belgium/The Netherlands nor among USA military personnel. Adv36 infection has also been shown to reduce blood lipid levels, increase glucose uptake by adipose tissue and skeletal muscle biopsies, and to associate with improved glycemic control in non-diabetic individuals.

PRINCIPAL FINDINGS

Using a novel ELISA, 1946 clinically well-characterized individuals including 424 children and 1522 non-diabetic adults, and 89 anonymous blood donors, residing in central Sweden representing the population in Stockholm area, were studied for the presence of antibodies against Adv36 in serum. The prevalence of Adv36 positivity in lean individuals increased from ∼7% in 1992-1998 to 15-20% in 2002-2009, which paralleled the increase in obesity prevalence. We found that Adv36-positive serology was associated with pediatric obesity and with severe obesity in females compared to lean and overweight/mildly obese individuals, with a 1.5 to 2-fold Adv36 positivity increase in cases. Moreover, Adv36 positivity was less common among females and males on antilipid pharmacological treatment or with high blood triglyceride level. Insulin sensitivity, measured as lower HOMA-IR, showed a higher point estimate in Adv36-positive obese females and males, although it was not statistically significant (p = 0.08).

CONCLUSION

Using a novel ELISA we show that Adv36 infection is associated with pediatric obesity, severe obesity in adult females and lower risk of high blood lipid levels in non-diabetic Swedish individuals.

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.

Surrogate estimates of insulin sensitivity in obese youth along the spectrum of glucose tolerance from normal to prediabetes to diabetes

CONTEXT

In epidemiological studies of childhood obesity, simple and reliable surrogate estimates of insulin sensitivity are needed because the gold standard, the hyperinsulinemic-euglycemic clamp, is not feasible on a large scale.

OBJECTIVE

To examine the correlation of fasting and oral glucose tolerance test (OGTT)-derived surrogate indices of insulin sensitivity with the hyperinsulinemic-euglycemic clamp in obese adolescents with normal glucose tolerance, prediabetes, and diabetes.

PATIENTS AND DESIGN

A total of 188 overweight/obese adolescents (10 to <20 yr old) who completed a standard 2-h OGTT and 3-h hyperinsulinemic-euglycemic clamp were included. Fasting-derived surrogates [fasting glucose (G(F)), fasting insulin (I(F)), 1/I(F), G(F)/I(F), homeostasis model assessment and quantitative insulin sensitivity check index] and OGTT-derived surrogates [whole-body insulin sensitivity index and the ratio of glucose and insulin areas under the curve (Gluc(AUC)/Ins(AUC))] were calculated.

MAIN OUTCOME MEASURES

We evaluated the correlations between the clamp-measured insulin sensitivity and the surrogate estimates and area under the receiver operating characteristic curves.

RESULTS

Fasting indices (1/I(F), G(F)/I(F), homeostasis model assessment of insulin sensitivity, and quantitative insulin sensitivity check index) correlated significantly with clamp insulin sensitivity (r = 0.82, 0.78, 0.81, and 0.80, respectively), with lower correlations between the OGTT surrogates and clamp (whole-body insulin sensitivity index, r = 0.77; Gluc(AUC)/Ins(AUC), r = 0.62). The area under the receiver operating characteristic curves was more than or equal to 0.94 for all surrogates except Gluc(AUC)/Ins(AUC.) Across quartiles of clamp-measured insulin sensitivity, there was a significant overlap in individual values of I(F), 1/I(F), and G(F)/I(F).

CONCLUSION

In obese adolescents with normal or impaired glucose tolerance or diabetes, OGTT-derived surrogates do not offer any advantage over the simpler fasting indices, which correlate strongly with clamp insulin sensitivity. Surrogate indices of insulin sensitivity could be used in epidemiological studies but not to define insulin resistance in individual patients or research subjects.

HOMA-IR and QUICKI: decide on a general standard instead of making further comparisons

AIM

To limit further comparisons between the two fasting indices Homeostasis Model Assessment for Insulin Resistance (HOMA-IR) and Quantitative Insulin Sensitivity Check Index (QUICKI), and to examine their robustness in assessing insulin sensitivity.

METHODS

A total of 191 obese children and adolescents (age 13.9 ± 2.9 years, BMI SDS 6.1 ± 1.6), who had undergone a Frequently Sampled Intravenous Glucose Tolerance Test (FSIVGTT), were included. Receiver operating characteristic curve (ROC) analysis was used to compare indices in detecting insulin resistance and Bland-Altman plots to investigate agreement between three consecutive fasting samples when compared to using single samples.

RESULTS

ROC analysis showed that the diagnostic accuracy was identical for QUICKI and HOMA-IR [area under the curve (AUC) boys 0.80, 95%CI 0.70-0.89; girls 0.80, 0.71-0.88], while insulin had a nonsignificantly lower AUC (boys 0.76, 0.66-0.87; girls 0.75, 0.66-0.84). Glucose did not perform better than chance as a diagnostic test (boys 0.47, 0.34-0.60; girls 0.57, 0.46-0.68). Indices varied with consecutive sampling, mainly attributable to fasting insulin variations (mean maximum difference in HOMA-IR -0.8; -0.9 to -0.7).

CONCLUSIONS

Using both HOMA-IR and QUICKI in further studies is superfluous as these indices function equally well as predictors of the FSIVGTT sensitivity index. Focus should be on establishing a general standard for research and clinical purposes.

Polycystic ovary syndrome in adolescence

The definition of polycystic ovary syndrome in very young girls is complicated by the fact that many features typical of the syndrome can also be seen as physiological stages in the maturation of the hypothalamus-pituitary-ovarian axis. The role of reduced insulin sensitivity in the pathogenesis and evolution of the disorder has gained more importance over recent years: both elevated androgen levels and being overweight may influence the impairment of glucose metabolism. Our study focused on 250 girls in the first 8 years of gynecological age. We analyzed the prevalence of different phenotypes according to the Rotterdam criteria and the impact of higher BMI on androgen levels and on fasting screening markers of glucose metabolism. In a smaller sample, we performed a more detailed evaluation of the glucose metabolism parameters; our findings indicated that in this age group, being overweight plays a major role in the deterioration of the clinical picture.

Modulation of gonadotropin-releasing hormone pulse generator sensitivity to progesterone inhibition in hyperandrogenic adolescent girls--implications for regulation of pubertal maturation

CONTEXT

Adult women with polycystic ovary syndrome (PCOS) have decreased GnRH pulse generator sensitivity to progesterone (P)-mediated slowing. This defect is androgen mediated because it is reversed with androgen receptor blockade. Adolescent hyperandrogenism often precedes PCOS.

OBJECTIVE

The aim of the study was to evaluate GnRH pulse generator sensitivity to P-mediated slowing in normal and hyperandrogenic girls.

DESIGN

We conducted a controlled interventional study.

SETTING

The study was conducted in a general clinical research center.

PARTICIPANTS

A total of 26 normal control (NC) and 26 hyperandrogenic (HA) girls were studied.

INTERVENTION

Frequent blood sampling was performed for 11 h to assess LH pulse frequency before and after 7 d of oral estradiol and P.

MAIN OUTCOME MEASURE

We measured the slope of the percentage reduction in LH pulse frequency as a function of d 7 P (slope).

RESULTS

Overall, Tanner 3-5 HA subjects were less sensitive to P-mediated slowing than Tanner 3-5 NC (slope, 4.7 +/- 3.4 vs. 10.3 +/- 7.7; P = 0.006). However, there was variability in the responses of HA subjects; 15 had P sensitivities within the range seen in NC, whereas nine were relatively P insensitive. The two groups had similar testosterone levels. Fasting insulin levels were higher in P-insensitive HA girls (39.6 +/- 30.6 vs. 22.2 +/- 13.9 microIU/ml; P = 0.02), and there was an inverse relationship between fasting insulin and P sensitivity in HA girls (P = 0.02). Tanner 1-2 NC had lower testosterone levels and were more P sensitive than Tanner 3-5 NC (slope, 19.3 +/- 5.8; P = 0.04).

CONCLUSIONS

Hyperandrogenism is variably associated with reduced GnRH pulse generator sensitivity to P-mediated slowing during adolescence. In addition to androgen levels, insulin resistance may modulate P sensitivity.

The effect of puberty on insulin resistance in obese children

OBJECTIVE

Insulin resistance (IR) increases during puberty in normal children. IR is the first adverse metabolic event of obesity, and the marker of the metabolic syndrome. We aimed to study the effect of puberty on IR in obese and normal-weight children.

DESIGN

Cross-sectional evaluation of fasting glucose, insulin concentrations, and homeostasis model assessment of IR (HOMA-IR) in obese and control children throughout puberty.

PATIENTS AND METHODS

We recruited 424 obese children (207 pre-pubertal and 217 pubertal divided in Tanner stages 2-3, 4, and 5) and estimated IR using the HOMA-IR index. Data were compared to those obtained in 123 healthy normal-weight children (40 pre-pubertal and 83 pubertal divided in Tanner stages 2-3, 4, and 5).

RESULTS

In the obese children mean HOMA-IR increased progressively across Tanner stages, and was significantly higher in all groups (pre-pubertal and Tanner stages 2-3, 4, and 5) of obese than in control children. HOMA-IR was significantly correlated with BMI.

CONCLUSIONS

HOMA-IR in obese children increases at puberty more than in normal-weight children and does not return to pre-pubertal values at the end of puberty.

Genetic variance in the adiponutrin gene family and childhood obesity

Aim

The adiponutrin gene family consists of five genes (PNPLA1-5) coding for proteins with both lipolytic and lipogenic properties. PNPLA3 has previously been associated with adult obesity. Here we investigated the possible association between genetic variants in these genes and childhood and adolescent obesity.

Methods/Results

Polymorphisms in the five genes of the adiponutrin gene family were selected and genotyped using the Sequenom platform in a childhood and adolescent obesity case-control study. Six variants in PNPLA1 showed association with obesity (rs9380559, rs12212459, rs1467912, rs4713951, rs10947600, and rs12199580, p<0.05 after adjustment for age and gender). Three variants in PNPLA3 showed association with obesity before, but not after, adjustment for age and gender (rs139051, rs12483959, and rs2072907, p>0.05). When analyzing these SNPs in relation to phenotypes, two SNPs in the PNPLA3 gene showed association with insulin sensitivity (rs12483959: β = −0.053, p = 0.016, and rs2072907: β = −0.049, p = 0.024). No associations were seen for PNPLA2, PNPLA4, and PNPLA5.

Conclusions

Genetic variation in the adiponutrin gene family does not seem to contribute strongly to obesity in children and adolescents. PNPLA1 exhibited a modest effect on obesity and PNPLA3 on insulin sensitivity. These data, however, require confirmation in other cohorts and ethnic groups.

Insulin sensitivity, VO2max and body composition in severely obese Swedish children and adolescents

AIM

The aim of this study was to identify relationships between insulin sensitivity (SI), cardiorespiratory fitness and body composition in severely obese Swedish children and adolescents.

METHODS

Two hundred and twenty-eight obese children (119 girls, 8-16 years, body mass index (BMI) 23.2-57.0 kg/m(2)) performed a frequently sampled intravenous glucose tolerance test (FSIVGTT), a submaximal bicycle ergometry test and a dual-energy X-ray absorptiometry (DEXA).

RESULTS

Mean SI (SD) was 0.38 (0.32) (x10(-5)/min/pM). SI correlated positively with relative body mass (BM) VO(2)max (r = 0.42) (p < 0.001), relative fat-free mass (FFM) VO(2)max (r = 0.36) (p < 0.001) and negatively with body mass index standard deviation score (BMI SDS) (r =-0.22) (p = 0.001). SI did not correlate with percent body fat (r =-0.01) and absolute VO(2)max (r = 0.01). In multiple regression analyses with SI as dependent variable, VO(2)max and body composition, together with gender, age and Tanner stage, explained 20-26% of the variance.

CONCLUSION

Relative (BM) VO(2)max and relative (FFM) VO(2)max were stronger predictors of SI than percent body fat in severely obese children and adolescents. The study confirms that cardiorespiratory fitness is of importance for the metabolic syndrome in the studied population. Efforts to improve SI should include physical activity targeting cardiorespiratory fitness also in severely obese children and adolescents.

Adiposity measures as indicators of metabolic risk factors in adolescents

AIM

To examine the relation between adiposity assessment methods (percentage body fat (%BF), BMI, and waist circumference (WC)) and individual metabolic risk factors (f-insulin, HDL cholesterol, triglycerides) and a combined measure of metabolic risk.

METHODS

Crosssectional study of 300 males (BMI 20.8 +/- 3.0 kg/m(2)) and females (BMI 21.3 +/- 2.9 kg/m(2)) 17 years of age. F-insulin and components of the metabolic syndrome defined by the International Diabetes Federation (IDF) were used as metabolic risk indicators, with samples stratified into BMI, %BF, and WC groups, respectively. Diagnostic accuracy was expressed as the area under the ROC curve (AUC).

RESULTS

In males, diagnostic accuracy for HDL and f-insulin was poor to fair for BMI (AUC 0.70, p = 0.001; 0.60, p = 0.22), WC (0.68, p = 0.003; 0.63, p = 0.11), and %BF (0.65, p = 0.009; 0.66, p = 0.04). The diagnostic accuracy for triglycerides was greater for all three measures (BMI 0.92, WC 0.95, %BF 0.87; all p < 0.001). For females, neither test performed better than chance for f-insulin and HDL, and only %BF performed better than chance for triglycerides (0.65, p = 0.08). All three measures exhibited higher accuracy for presence of > or =2 metabolic risk factors (AUCs 0.76-0.91, p < 0.001) in both sexes.

CONCLUSION

%BF was not superior to BMI and WC for detecting metabolic risk in the general adolescent population.