Limited accuracy of surrogates of insulin resistance during puberty in obese and lean children at risk for altered glucoregulation

Fasting Serum IGFBP-1 as a Marker of Insulin Resistance in Diverse School Age Groups

Introduction

The known markers of insulin resistance in obese children are well studied. However, they require serial measurements and complicated calculations. The objective is to study IGFBP-1 and its relation with other known risk measures.

Materials and Methods

The study included 98 New York City school students of diverse ethnic/racial backgrounds (57 males and 41 females), 11-15 years of age. Subjects were enrolled in a cross-sectional study, and anthropometric measures were collected. They underwent fasting intravenous glucose tolerance tests (IVGTT), and glucose, insulin, lipids, IGFBP-1, adiponectin and inflammatory markers were collected.

Results

The subjects were stratified into 3 groups based upon the BMI Z-score. Out of all the subjects, 65.3% were in the group with a BMI Z-score <1 SDS, 16.3% subjects were in the group with a BMI Z-score of 1 to 2 SDS, and 18.4% of the subjects were in the group with a BMI Z-score of more than 2 SDS. The group with a BMI Z-score of more than 2 SDS had increased waist circumference (WC), body fat, increased fasting insulin, and triglycerides (TG). This group had decreased levels of adiponectin and HDL and low IGFBP-1 as compared to the group with BMI <1 SDS. The group with a BMI Z-score of 1 to 2 SDS had a decreased level of IGFBP-1 as compared to the group with a BMI Z-score less than 1 SDS. IGFBP-1 inversely correlated with age, WC, BMI, body fat, TG, and insulin levels. IGFBP-1 positively correlated with adiponectin and HDL levels.

Conclusion

IGFBP-1 in children can identify the presence of insulin resistance in the group with BMI 1 to 2 SDS, even before the known markers of insulin resistance such as elevated triglycerides and even before decreased HDL and adiponectin levels are identified.

Comparative Informativity of Computing Methods of Insulin Resistance Assessment

We conducted a comparative study of the calculated indices of insulin resistance HOMA-R, Caro, FGIR, and QUICKI in 29 healthy volunteers (mean age 26.21±0.93 years) with normal body mass index (23.34±0.55 kg/m2). Among the used methods for insulin resistance assessment, QUICKI is the only method that has characteristics required for the diagnostic criterium: low variability coefficient, 100% reproducibility, and minimum coefficient of variation.

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.

Effects of low glycaemic index/low glycaemic load vs. high glycaemic index/ high glycaemic load diets on overweight/obesity and associated risk factors in children and adolescents: a systematic review and meta-analysis

The objective of the present systematic review and meta-analysis was to synthesize the available literature data investigating the effects of low glycaemic index/low glycamic load dietary regimens on anthropometric parameters, blood lipid profiles, and indicators of glucose metabolism in children and adolescents. Literature search was performed using the electronic databases MEDLINE, EMBASE, and the Cochrane Central Register of trials with restrictions to randomized controlled trials, but no limitations concerning language and publication date. Parameters taken into account were: body weight, body mass index, z-score of body mass index, fat mass, fat-free mass, height, waist cicrumference, hip circumference, waist-to-hip ratio, total cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides, diastolic and systolic blood pressure, fasting serum glucose, fasting serum insulin, HOMA-index, glycosylated haemoglobin, and C-reactive protein. Meta-analyses were performed for each parameter to assess pooled effect in terms of weighted mean differences between the post-intervention (or differences in means) of the low glycaemic index diets and the respective high glycaemic index counterparts. Data analysis was performed using the Review Manager 5.3. software. Nine studies enrolling 1.065 children or adolescents met the inclusion criteria. Compared to diets providing a high gylcaemic index, low glycaemic index protocols resulted in significantly more pronounced decreases in serum triglycerides [mean differences −15.14 mg/dl, 95 %-CI (−26.26, −4.00)] and HOMA-index [mean difference −0.70, 95 %-CI (−1.37, −0.04), fixed-effects model only]. Other parameters under investigation were not affected by either low or high glycaemic indices. The present systematic review and meta-analysis provides evidence of a beneficial effect of a low glycaemic index/load diet in children and adolescents being either overweight or obese. Regarding the limitations of this analysis, further studies adopting a homogenous design are necessary to assure the present findings. Since low glycaemic index/load regimens were not associated with a deterioration of the outcome parameters, these diets should not be categorically excluded when looking for alternatives to change lifestyle habits in this age group.

Impact of exercise training without caloric restriction on inflammation, insulin resistance and visceral fat mass in obese adolescents

BACKGROUND

Exercise training has been shown to improve cardiometabolic health in obese adolescents.

OBJECTIVES

Evaluate the impact of a 12-week exercise-training programme (without caloric restriction) on obese adolescents' cardiometabolic and vascular risk profiles.

METHODS

We measured systemic markers of oxidation, inflammation, metabolic variables and endothelial function in 20 obese adolescents (OB) (age: 14.5 ± 1.5 years; body mass index: 34.0 ± 4.7 kg m(-2) ) and 20 age- and gender-matched normal-weight adolescents (NW). Body composition was assessed by magnetic resonance imagery. Peak aerobic capacity and maximal fat oxidation were evaluated during specific incremental exercise tests. OB participated in a 12-week exercise-training programme.

RESULTS

OB presented lower peak aerobic capacity (24.2 ± 5.9 vs. 39.8 ± 8.3 mL kg(-1)  min(-1) , P < 0.05) and maximal fat oxidation compared with NW (P < 0.05). OB displayed greater F2t-Isoprostanes (20.5 ± 6.7 vs. 13.4 ± 4.2 ng mmol(-1) creatinine), Interleukin-1 receptor antagonist (IL-1Ra) (1794.8 ± 532.2 vs. 835.1 ± 1027.4 pg mL(-1) ), Tumor Necrosis Factor-α (TNF-α) (2.1 ± 1.2 vs. 1.5 ± 1.0 pg mL(-1) ), Soluble Tumor Necrosis Factor-α Type II Receptor (sTNFαRII), leptin, insulin, homeostasis model assessment of insulin resistance, version 2 (HOMA2-IR), high-sensitive C-reactive protein, triglycerides and lower adiponectin and high-density lipoprotein cholesterol (all P < 0.05). After exercise training, despite lack of weight loss, VO2peak (mL.kg(-1) .min(-1) ) and maximal fat oxidation increased (P < 0.05). IL-1Ra and IFN-gamma-inducible protein 10 (IP-10) decreased (P < 0.05). Insulin and HOMA2-IR decreased (14.8 ± 1.5 vs. 10.2 ± 4.2 μUI mL(-1) and 1.9 ± 0.8 vs. 1.3 ± 0.6, respectively, P < 0.05). Change in visceral fat mass was inversely associated with change in maximal fat oxidation (r = -0.54; P = 0.024). The subgroup of participants that lost visceral fat mass showed greater improvements in triglycerides, insulin resistance and maximal fat oxidation.

CONCLUSION

Our data confirms the role of exercise training on improving the inflammatory profile and insulin resistance of OB in the absence of weight loss. However, those who lost a greater amount of visceral fat mass showed greater benefits in terms of insulin profile, triglycerides and maximal fat oxidation.

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.

Glucose homeostasis and insulin resistance: prevalence, gender differences and predictors in adolescents

BACKGROUND

Adolescence, due to transient pubertal insulin resistance (IR), is associated with a higher risk for disturbances of glucose metabolism. The aim of our study was 1) to investigate the prevalence of disturbances of glucose metabolism, 2) to define gender specific homeostasis model assessment of insulin resistance (HOMA-IR) thresholds associated with increased cardiometabolic risks and 3) to provide predictors of HOMA-IR.

METHODS

The studied cohort consisted of Czech adolescents aged 13.0-17.9 years: 1,518 individuals of general population and three studied groups according weight category (615 normal weight, 230 overweight and 683 obese). The prevalence of IR, impaired fasting glucose (IFG) and type 2 diabetes was assessed. Risky HOMA-IR thresholds based on components of metabolic syndrome were investigated. HOMA-IR prediction was calculated taking into account age, blood pressure, multiple anthropometric, biochemical and hormonal parameters.

RESULTS

In general population cohort, the prevalence of IFG and type 2 diabetes was 7.0% and <0.5%, respectively. Boys regardless of weight presented significantly higher levels of blood glucose and higher prevalence of IFG than girls. Obese boys were found more insulin resistant than obese girls. HOMA-IR thresholds of 3.6 for girls and 4.4 for boys were associated with increased cardiometabolic risks. For both genders, the model of HOMA-IR prediction was composed of age, BMI, ratio of free triiodthyronine to free thyroxine, gamma-glutamyltransferase activity and levels of triglycerides and sex hormone-binding globulin.

CONCLUSIONS

The type 2 diabetes in adolescents, including those who were obese, was rarely diagnosed. Obese adolescent boys were at greater risk for IR and for IFG than obese girls. In adolescence, thresholds of HOMA-IR in contrast to predictors were found gender specific.

Association of osteocalcin with obesity, insulin resistance, and cardiovascular risk factors in young adults

Low levels of osteocalcin (OCN), an osteoblast-specific hormone, have recently been associated with insulin resistance (homeostasis model assessment-insulin resistance (HOMA-IR)) and obesity, particularly in older adults. The aim of this study was to determine whether low levels of OCN would be associated with insulin resistance, obesity, and greater cardiovascular (CV) risk in young adults just emerging from adolescence. Undercarboxylated OCN and carboxylated OCN levels were measured on stored serum samples (total OCN = undercarboxylated OCN + carboxylated OCN) on 137 participants (67 males) at mean age 18.6 years (range 17-22 years). Insulin resistance was measured by hyperinsulinemic-euglycemic clamp (M(lbm)). Multivariable regression analyses with ln(OCN) as the independent variable were adjusted for age, sex, ethnicity, and BMI as indicated. Total OCN was inversely related to BMI, waist circumference, systolic blood pressure (SBP), interleukin (IL)-6, and directly related to M(lbm); only SBP remained significant (with M(lbm) P = 0.0560) after further adjustment for BMI. Carboxylated OCN was inversely related to BMI, waist circumference, SBP, low-density lipoprotein cholesterol (LDL-C), and directly related to adiponectin; SBP and adiponectin remained significant after further adjustment for BMI. There were no significant associations with undercarboxylated OCN. In summary, most associations with OCN were mediated via BMI. However, the significant associations of OCN with SBP, obesity, and adiponectin and borderline with M(lbm), suggest a potential role for OCN in the development of insulin resistance and CV risk that becomes more apparent with aging into older adulthood.

Endothelial dysfunction, inflammation, and oxidative stress in obese children and adolescents: markers and effect of lifestyle intervention

With an increasing prevalence, pediatric obesity is often a prelude to adulthood obesity, and represents a major public health issue. Comorbidities are very common and severe in obese adults, justifying the search for earlier markers or risk factors for cardiovascular diseases in obese children. Endothelial dysfunction has been found to be present in the early stages of atherosclerosis, and can be non-invasively assessed with widely accepted and well-standardized techniques at the macrocirculation level. Endothelial dysfunction at the microcirculation level is less documented in obese children. Obesity in children has been repeatedly and independently correlated to endothelial dysfunction, inflammation and oxidative stress markers, although the relationship between these factors remains to be investigated. However, this would not only allow substantial improvements in risk stratification, but also provide essential data regarding the evolution of endothelial dysfunction in childhood obesity, especially during puberty when pro-inflammatory and pro-oxidative changes, with relative insulin resistance, occur. Therapeutic strategies such as lifestyle interventions in early childhood obesity appear all the more necessary, optimally including both exercise and diet because of their known effects on inflammatory and oxidative stress markers, potentially reversing endothelial dysfunction.

Prevention and current onset delay approaches of type 2 diabetes mellitus (T2DM)

The urgent need to treat type 2 diabetes mellitus (T2DM), which is currently reaching epidemic proportions, has been a major focus of healthcare systems and policy makers worldwide. Pharmacological treatment and lifestyle interventions together with the control of cardiovascular risk factors are the main strategies to prevent or delay the onset of T2DM. The present review discusses the state of the art knowledge of effective therapeutic approaches (metformin, thiazolidinediones, nateglinides, α-glucosidase inhibitors, incretin-based and angiotensin-based therapies, weight reducers, statins, fibric acid derivatives), including surgery, and identifies the major lifestyle changes for specific target groups.

Insulin resistance in children: consensus, perspective, and future directions

OBJECTIVE

Emerging data indicate that insulin resistance is common among children and adolescents and is related to cardiometabolic risk, therefore requiring consideration early in life. However, there is still confusion on how to define insulin resistance, how to measure it, what its risk factors are, and whether there are effective strategies to prevent and treat it. A consensus conference was organized in order to clarify these points.

PARTICIPANTS

The consensus was internationally supported by all the major scientific societies in pediatric endocrinology and 37 participants.

EVIDENCE

An independent and systematic search of the literature was conducted to identify key articles relating to insulin resistance in children.

CONSENSUS PROCESS

The conference was divided into five themes and working groups: background and definition; methods of measurement and screening; risk factors and consequences; prevention; and treatment. Each group selected key issues, searched the literature, and developed a draft document. During a 3-d meeting, these papers were debated and finalized by each group before presenting them to the full forum for further discussion and agreement.

CONCLUSIONS

Given the current childhood obesity epidemic, insulin resistance in children is an important issue confronting health care professionals. There are no clear criteria to define insulin resistance in children, and surrogate markers such as fasting insulin are poor measures of insulin sensitivity. Based on current screening criteria and methodology, there is no justification for screening children for insulin resistance. Lifestyle interventions including diet and exercise can improve insulin sensitivity, whereas drugs should be implemented only in selected cases.

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.

Insulin resistance indexes in renal transplant recipients maintained on tacrolimus immunosuppression

BACKGROUND

Insulin resistance is common posttransplantation and contributes to both new onset diabetes after transplantation and the metabolic syndrome. Insulin resistance indexes have never been validated in transplant recipients on tacrolimus compared with cyclosporine, although it is more diabetogenic. We aimed to assess these indexes in renal transplant recipients on tacrolimus as primary immunosuppressant.

METHODS

Retrospective analysis of 76 frequently sampled, intravenous glucose tolerance tests (for insulin sensitivity) in 38 nondiabetic renal transplant recipients on tacrolimus-centered immunosuppression. Indexes tested were fasting glucose/insulin ratio, homeostasis model assessment (HOMA) index, 1/HOMA, log (HOMA), quantitative insulin sensitivity check index, and the McAuley's index. Indexes were also compared against waist/hip ratio and C-reactive protein (CRP). Multivariate linear regression analysis was performed to determine independent variables predictive for insulin resistance.

RESULTS

Insulin sensitivity successfully correlated with all indexes: fasting glucose/insulin ratio (r=0.246, P=0.033), HOMA index (r=-0.240, P=0.038), 1/HOMA (r=0.282, P=0.014), log (HOMA) (r=-0.316, P=0.006), quantitative insulin sensitivity check index (r=0.320, P=0.005), and McAuley's index (r=0.323, P=0.005). McAuley's index also correlated strongest with waist/hip ratio (r=-0.425, P<0.001). All indexes failed to correlate with CRP. Variables independently associated with insulin sensitivity were HbA1c (r=0.189, P=0.019), pulse pressure (r=0.146, P=0.021), and CRP (r=0.210, P=0.010).

CONCLUSIONS

Insulin resistance indexes are valid in transplant recipients taking tacrolimus, with McAuley's index the strongest surrogate.

Is islet autoimmunity related to insulin sensitivity or body weight in children of parents with type 1 diabetes?

AIMS/HYPOTHESIS

It has been suggested that metabolic demand and insulin resistance play a role in the development of type 1 diabetes, including the onset of autoimmunity. The aim of the present study was to determine whether insulin demand is increased in children with islet autoantibodies.

METHODS

BMI standard deviation score (BMI-SDS) was measured from 2 years of age in 1,650 prospectively followed children of mothers or fathers with type 1 diabetes, including 135 who developed persistent islet autoantibodies. HOMA of insulin resistance (HOMA-IR) was determined using fasting samples from 777 of the children starting from age 5 years.

RESULTS

An increased HOMA-IR was associated with female sex (p = 0.0004), older age (p < 0.0001) and increased BMI-SDS (p < 0.0001). Children with islet autoantibodies did not have an increased HOMA-IR compared with age-matched islet autoantibody-negative children (age 8 years: mean 0.61 vs mean 0.72, respectively, p = 0.21; age 11 years: mean 0.96 vs mean 1.21, respectively, p = 0.07). Furthermore, after correction for age and sex, autoantibody positivity was associated with decreased HOMA-IR values (p = 0.01). BMI-SDS was similar between islet autoantibody-positive and -negative children at age 2 (mean 0.07 vs mean 0.16, respectively), 5 (mean 0.06 vs 0.08, respectively), 8 (mean - 0.09 vs mean 0.02, respectively), and 11 years (mean 0.22 vs mean 0.16, respectively) and similar to that of national reference values.

CONCLUSIONS/INTERPRETATION

Islet autoantibody-positive children in the BABYDIAB cohort are not insulin resistant and do not have an increased BMI around and early after islet autoantibody seroconversion. These findings are inconsistent with the notion that insulin resistance is a risk factor for islet autoimmunity.

Waist circumference percentile thresholds for identifying adolescents with insulin resistance in clinical practice

We formally evaluated waist circumference (WC) percentile cutoffs for predicting insulin resistance (IR) and whether different cutoffs should be used for adolescents of different race/ethnicities. Analysis was performed for 1575 adolescents aged 12-18 yr from the National Health and Nutrition Examination Survey 1999-2002. Adolescents were classified as having IR if they had a homeostasis model assessment-insulin resistance level, a validated measure of IR, of >4.39, and WC percentile was classified according to previously published universal (all races combined) and race/ethnicity-specific WC percentile cutoffs. Receiver operating characteristic curves for predicting IR were constructed comparing the race/ethnicity-specific vs. universal WC percentile cutoffs, and area under the curve (AUC) was calculated. Comparing universal with race/ethnicity-specific WC percentiles, there were no significant differences in AUC for Black, Mexican-American, or White adolescents. Because race/ethnicity-specific thresholds did not discriminate better than universal WC thresholds, universal WC thresholds may be used effectively to identify adolescents with IR in primary care practices. A WC > or =75th or > or =90th percentile for all race/ethnicities combined would be appropriate to apply in clinical practice for identification of adolescents with IR, a risk factor for development of type 2 diabetes.

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.

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.

Effects of two-month physical-endurance and diet-restriction programmes on lipid profiles and insulin resistance in obese adolescent boys

AIM

The aim of this study was to assess the impact of a two-month programme of physical endurance and dietary restriction, alone and combined, on plasma lipids and insulin resistance in obese adolescents.

METHODS

A total of 24 obese adolescent boys participated in programmes of either dietary restriction (R), physical endurance at the point of maximum lipid oxidation (LIPOX(max)) (E) or diet combined with training (R+E). Anthropometric characteristics, metabolic measures and biochemical analyses were performed in all subjects before and after the interventions. An estimated insulin resistance was calculated using the homoeostasis model assessment (HOMA-IR) index.

RESULTS

At the end of the two-month programmes, adolescents in the R+E group showed greater reductions in body mass index (-3.9+/-0.7 kg/m(2)) and waist circumference (-12.3+/-4.8 cm) (P<0.001) than either the R or E group. A significant decrease (P<0.01) in HOMA-IR index (-2.13+/-0.11), plasma triglycerides, LDL and total cholesterol was also seen in the R+E group. Moreover, at the end of the programme, the ratio of HDL cholesterol to triglycerides was significantly increased from baseline in the R+E group (0.93+/-0.09 vs. 0.68+/-0.11; P<0.01).

CONCLUSION

Compared with either moderate physical endurance or dietary restriction, a combination of both resulted in a significant decrease in cardiovascular risk factors and HOMA-IR index in obese adolescent boys.

Insulin resistance and impaired glucose tolerance in overweight and obese Costa Rican schoolchildren

BACKGROUND

Worldwide obesity has become an unprecedented public health challenge. In addition, a notable increase in the risk of insulin resistance and type 2 diabetes mellitus has emerged. In Costa Rica, there are no epidemiological data to establish the prevalence of type 2 diabetes in the pediatric population. However, information from the Endocrinology Department of the Children's National Hospital indicates an increased number of cases in the last 2 to 3 years.

OBJECTIVE

To determine the prevalence of insulin resistance and impaired glucose tolerance in overweight and obese schoolchildren.

METHODS

This cross-sectional study was conducted among 214 healthy 8- to 10-year-old children from urban schools of San José, Costa Rica. Anthropometric measurements and blood determinations of glucose, insulin, proinsulin, glycosylated hemoglobin, C-peptide, and leptin were performed. Indexes were calculated to assess insulin resistance. Information on social and lifestyle variables was obtained from questionnaires, and acanthosis nigricans was certified by a physician. Statistical analysis was performed with SPSS software for Windows, version 10.0.

RESULTS

The prevalence of type 2 diabetes mellitus was very low (0.5%) in the studied population. However, hyperinsulinemia and impaired glucose tolerance were present in 20.6% and 6.5% of the subjects, respectively. On the basis of the Fasting Glucose-to-Insulin Resistance Ratio (FGIR), 46.7% of the children showed insulin resistance. Girls and obese children (body mass index > or = 95th percentile) were more likely to have higher serum insulin levels and insulin resistance than boys and overweight children (BMI > or = 85th percentile). Compared with the lowest quintile, children in the highest quintile of body-fat tissue had higher insulin resistance but had similar serum concentrations of glucose, C-peptide, and proinsulin. Positive family histories of type 2 diabetes mellitus and sedentarism (73.7% and 40.7%, respectively) were highly prevalent among overweight and obese children.

CONCLUSIONS

The prevalence of impaired glucose tolerance and insulin resistance in obese children indicates a worrisome trend in the incidence of type 2 diabetes in Costa Rica. Strategies for weight reduction, obesity prevention, and promotion of healthy lifestyles are necessary to prevent the onset of type 2 diabetes during childhood and adolescence.

No difference in insulin resistance and lipid levels between controls and adolescent subjects who later develop psychosis

Type 2 diabetes and dyslipidemias co-occur frequently with psychoses, but it is not known how common they are in adolescents who later develop psychosis. We investigated waist circumference, blood glucose, lipid and insulin levels and insulin resistance in the Northern Finland 1986 Birth Cohort at the age of 15/16 (N=5410). The Social Insurance Institute register and the Finnish Hospital Discharge Register were used to find the participants who developed psychosis (N=21), and they were compared with other participants. There were no differences in the cardiometabolic variables, suggesting that psychotic episode is not preceded by glucose and lipid metabolism disturbances.

Longitudinal changes in insulin sensitivity and body composition of small-for-gestational-age adolescents after cessation of growth hormone treatment

CONTEXT

GH treatment reduces insulin sensitivity (Si). For small-for-gestational-age (SGA) subjects, who might have an increased risk to develop cardiovascular disease and type 2 diabetes, it is still uncertain how Si, beta-cell function, and body composition change over time after stopping GH treatment.

OBJECTIVE

Our objective was to investigate longitudinal changes in Si, beta-cell function, and body composition after cessation of long-term GH treatment.

DESIGN AND PATIENTS

We conducted a longitudinal study that included 48 SGA adolescents studied at adult height, while still on GH, and 6 months after GH stop and compared them with 38 appropriate-for-gestational-age (AGA) controls at both time points.

OUTCOME MEASURE

We took paired measurements of Si and beta-cell function, assessed by frequently sampled iv glucose tolerance tests with tolbutamide, and body composition, measured by dual-energy x-ray absorptiometry.

RESULTS

After stopping GH, Si (P = 0.006), glucose effectiveness (Sg; P = 0.009) and beta-cell function (disposition index; P = 0.024) increased, whereas insulin secretion (acute insulin response; not significant) decreased. Fat percentage increased (P < 0.0005), and lean body mass decreased (P < 0.0005), but fat distribution remained unaltered, and body composition remained within the normal range. Compared with AGA controls, Si was lower during GH and became similar after GH stop, acute insulin response was higher at both time points, and glucose effectiveness and disposition index became higher.

CONCLUSIONS

The GH-induced lower Si in SGA adolescents increases after stopping long-term GH treatment and becomes similar to that of AGA controls. Discontinuation of GH treatment is, however, also associated with an increase in percent body fat and with a decrease in lean body mass, without changes in fat distribution.

[Insulin therapy for type 1 diabetes mellitus: past and present]

The discovery of insulin can be considered the milestone of diabetes mellitus history and a great achievement for its treatment. The first insulin available was the regular. Afterwards, Hagedorn added the protamine to the insulin, thus, creating the NPH insulin. In the 1950s an insulin free of protamine was synthesized: the lente insulin. With the advent of molecular biology, synthetic human insulin was synthesized using recombinant DNA technology. Most recently several types of insulin analogues were available, providing the patients with better metabolic control. Type 1 diabetes mellitus treatment includes plain substitution and individualization for short-acting plus long-acting insulin according to the physician's assistance, besides regular practice of physical activities and diet orientations. In type 1 diabetes mellitus the insulin of low variability is the best choice since basal/bolus insulin therapy or continuous subcutaneous insulin infusion pump can mimetize the physiological release of insulin by beta cells.

Measurement of insulin sensitivity in children: comparison between the euglycemic-hyperinsulinemic clamp and surrogate measures

OBJECTIVE

In this study we compared fasting insulin and measures of insulin sensitivity (M) based on fasting insulin and glucose (i.e., homeostasis model assessment [HOMA], quantitative insulin sensitivity check index [QUICKI], and fasting glucose-to-insulin ratio [FGIR]) or triglycerides to the insulin clamp in a cohort of children/adolescents.

RESEARCH DESIGN AND METHODS

The subjects were Minneapolis fifth- to eighth-grade students. Euglycemic-hyperinsulinemic clamps were performed on 323 adolescents at mean age 13 and were repeated on 300 of these subjects at mean age 15. Insulin sensitivity was determined by glucose uptake (milligrams per kilogram per minute) adjusted for lean body mass (M(LBM)) and steady-state insulin (M(LBM)/ln SSI). Comparisons were made for the whole cohort and by body size (BMI < 85th percentile vs. BMI > or = 85th percentile). Receiver operating characteristic (ROC) curves were used to test whether specific fasting insulin cut points separated true-positive from false-positive approximations of insulin resistance.

RESULTS

Fasting insulin was significantly correlated with HOMA (r = 0.99), QUICKI (r = 0.79), FGIR (r = -0.62), and (ln fasting insulin + ln triglycerides) (r = 0.88). Correlations of the surrogates with M(LBM) were significantly lower than those with M for the total cohort and > or = 85th percentile group. In general, correlations in the > or = 85th percentile group were higher than those in the < 85th percentile group. Correlations with M(LBM) and M(LBM)/ln SSI decreased in the total cohort and > or = 85th percentile group from age 13 to 15. ROC curves showed only a modest capability to separate true- from false-positive values.

CONCLUSIONS

Surrogate measures are only modestly correlated with the clamp measures of insulin sensitivity and do not offer any advantage over fasting insulin. In general, lower correlations are seen with M(LBM) than with M and with thinner than with heavier individuals.

Alternative methods of insulin sensitivity assessment in obese children and adolescents

OBJECTIVE

To validate fasting indexes against minimal model analysis (MMOD) of the frequently sampled intravenous glucose tolerance test (FSIVGTT) in an obese pediatric population.

RESEARCH DESIGN AND METHODS

FSIVGTT-MMOD results were compared with homeostasis model assessment of insulin resistance (HOMA-IR) and fasting insulin with the sample stratified by sex, puberty, and sensitivity index (S(i)) median in 191 children (82 males and 109 females, 13.9 +/- 2.9 years of age, BMI 36.9 +/- 6.2 kg/m(2), BMI SD score 6.1 +/- 1.6).

RESULTS

Across pubertal groups, correlation coefficients between S(i) and HOMA-IR ranged from -0.43 to -0.78 in males and from -0.53 to -0.57 in females (age and BMI adjusted, P < 0.05 in all instances). Similar results were seen for fasting insulin. In females, the relationship was significantly weaker in more-insulin-resistant subjects.

CONCLUSIONS

The validity of fasting indexes in explaining S(i) was sex dependent, varied with pubertal stage, and in females was influenced by degree of insulin sensitivity. In obese pediatric populations, we generally discourage the use of fasting indexes, although the validity varies within subgroups.

Insulin resistance and progression to type 1 diabetes in the European Nicotinamide Diabetes Intervention Trial (ENDIT)

OBJECTIVE

Insulin resistance can modulate progression to type 1 diabetes in individuals with ongoing islet autoimmunity. We wanted to see whether measures of insulin resistance improved risk assessment in islet cell antibody (ICA)-positive relatives when added to other immune and metabolic markers.

RESEARCH DESIGN AND METHODS

The retrospective cohort analysis included 213 family members participating in the European Nicotinamide Diabetes Intervention Trial. All were aged <25 years, with at least one islet antibody in addition to ICA >or=20 Juvenile Diabetes Foundation units. Median length of follow-up was 4.21 years, and 105 individuals developed diabetes. Oral and intravenous glucose tolerance tests were performed at baseline; antibodies to GAD, IA-2, and insulin were determined by radioimmunoassay; and insulin resistance was estimated by homeostasis model assessment. Risk was assessed by Cox regression analysis

RESULTS

The overall cumulative risk of diabetes within 5 years was 54.1% (95% CI 46.0-62.3). Multivariate analysis confirmed that baseline first-phase insulin response (FPIR) quartile (P < 0.0001), number of additional antibody markers (P < 0.0001), and 120-min glucose in the oral glucose tolerance test (P < 0.0001) were independent determinants of risk of progression, whereas addition of homeostasis model assessment of insulin resistance (HOMA2-IR) achieved only borderline significance (P = 0.06). HOMA2-IR was an independent determinant in participants with loss of FPIR (P = 0.025) but not in those with preserved FPIR (P = 0.3).

CONCLUSIONS

These data suggest that insulin resistance accelerates progression to type 1 diabetes in antibody-positive relatives in whom insulin secretion is markedly reduced but does not affect progression when insulin secretion is relatively well preserved.

Prediabetes in rural and urban children in 3 states in Mexico

The authors studied the frequency, distribution, and factors associated with prediabetes (fasting glucose, 100-125 mg/dL) in rural and urban children from San Luis Potosí, León, and Querétaro in central Mexico. Family history, somatometry, and levels of fasting insulin, glucose, and lipids were collected in 1238 children 6 to 13 years of age. The authors found no cases of type 2 diabetes and a 5.7% frequency of prediabetes. The group with prediabetes had higher homeostasis model assessment of insulin resistance scores and total cholesterol and high-density lipoprotein cholesterol levels. Prediabetes was more frequent in León, with similar distribution in rural and urban children. The frequency of insulin resistance was 24.1%, with higher figures in urban groups and in San Luis Potosí. In multivariate analysis, prediabetes was associated with insulin resistance and residence in León. The authors concluded that in central Mexico the frequency of prediabetes is significant, and it is associated with insulin resistance and a geographic location, but not with obesity or urban vs rural dwelling.

Insulin-like growth factor binding protein-1 to screen for insulin resistance in children

BACKGROUND

Diabetes and atherosclerosis are burgeoning health problems complicating obesity-associated insulin resistance (IR). Early detection of IR in children is a key to preventative strategies. Since peripheral insulin levels insensitively reflect hepatic insulin fluxes, we studied the insulin-regulated hepatic insulin-like growth factor binding proteins (IGFBPs)-1 and -3 as possible screening markers of childhood IR.

METHODS

The tolbutamide-modified frequently sampled intravenous glucose tolerance test (FSIVGTT) and the oral glucose tolerance test (OGTT) were performed in 118 subjects < 21 years old with obesity. The relationships between insulin sensitivity index by minimal modeling (SiIVGTT), other Sis derived from fasting and OGTT insulin and glucose values, and the candidate serum markers were sought.

RESULTS

Significant correlation was found between IGFBP-1 and SiIVGTT, similar to the correlations of insulin sensitivity indices with SiIVGTT. In children < or = 10 years old, correlation of IGFBP-1 with SiIVGTT was the strongest. All (100%) subjects with IR defined by SiIVGTT < 4.5 +/- 0.5 x 10(-4) min(-1) /(microIU/mL) had inappropriately low IGFBP-1 levels. IGFBP-3 was not correlated with SiIVGTT.

CONCLUSIONS

IGFBP-1 levels decrease with obesity and IR. We propose that in young subjects, especially children under the age of 10 years, IGFBP-1 is a convenient and sensitive marker of IR, whereas elevated fasting insulin is less sensitive but more specific.

Evaluation of insulin sensitivity and glucose effectiveness during a standardized breakfast test: comparison with the minimal model analysis of an intravenous glucose tolerance test

There is a need for reliable measurements of insulin sensitivity (SI) simpler than the euglycemic hyperinsulinemic clamp or the intravenous glucose tolerance test (IVGTT), which could be used when the simpler surrogates based on fasting insulin (Ib) and glucose (Gb) lose their validity. Several evaluations of SI derived from oral glucose tolerance test (OGTT) or its physiologic form, the standardized breakfast test (SBT), have been proposed. We aimed at determining which SBT-derived measurements of SI give the best prediction of the values obtained with the minimal model analysis of an IVGTT. Twenty-eight subjects (23 females and 5 males; age, 44.3+/-0.6 years) with a wide range of glucose tolerance randomly underwent a hyperglucidic SBT and an IVGTT with minimal model analysis. Correlations of 35 indices (converted if appropriated into similar units) with IVGTT-derived SI were calculated, and the accuracy of the empiric formulas obtained with the 11 best predictions were evaluated with Bland-Altman plots. Subjects covered all the spectrum of SI between 0.19 and 21.3 min-1/(microU.mL-1)x10(-4). Eight procedures yielded satisfactory predictions of minimal model SI: (1) SI (from Matsuda's composite index)=-1.24+65/(IbGbImGm)-0.5; (2) SI=1.89+2690/(IbGbImGm); (3) SI (from Bennett's index)=-2.93+5.16/(log Ibxlog Gb); (4) SI (from Sluiter's index)=0.2+2400/(IpGp); (5) SI=-8.54+38.4/(Belfiore's ISI index); (6) SI (from Cederholm's formula)=76/(Gm log Im); (7) SI=0.248+0.947/GbIm; (8) SI (from Mari's "oral glucose insulin sensitivity" index)=oral glucose insulin sensitivity/Ip; (9) Caumo's model. Glucose effectiveness Sg can also be accurately predicted by the following formula: Sg=2.921e-0.185(G60- Gb) (Ip=insulin peak; Gp=glucose peak; Ia=insulin area; Ga=glucose area; G60=glycemia at 60 minutes). The hyperglucidic SBT can provide accurate evaluations of SI and Sg, either by elaborated models or by simple empiric formulas.

The rise and fall of insulin secretion in type 1 diabetes mellitus

An understanding of the natural history of beta cell responses is an essential prerequisite for interventional studies designed to prevent or treat type 1 diabetes. Here we review published data on changes in insulin responses in humans with type 1 diabetes. We also describe a new analysis of C-peptide responses in subjects who are at risk of type 1 diabetes and enrolled in the Diabetes Prevention Trial-1 (DPT-1). C-peptide responses to a mixed meal increase during childhood and through adolescence, but show no significant change during adult life; responses are lower in adults who progress to diabetes than in those who do not. The age-related increase in C-peptide responses may account for the higher levels of C-peptide observed in adults with newly diagnosed type 1 diabetes compared with those in children and adolescents. Based on these findings, we propose a revised model of the natural history of the disease, in which an age-related increase in functional beta cell responses before the onset of autoimmune beta cell damage is an important determinant of the clinical features of the disease.

Insulin and HOMA in Spanish prepubertal children: relationship with lipid profile

OBJECTIVE

The effects of insulin or insulin resistance on the lipid profile seem to change with age. The aim of this study was to analyze insulin levels and an insulin resistance index and to investigate the relationship between these and the lipid profile in a population-based sample of Spanish prepubertal children.

METHODS

1048 (524 boys and 524 girls) randomly selected prepubertal children were studied. Children were 6 to 8 years old with a mean age of 6.7. Plasma lipid, FFA and insulin levels were measured. The homeostatic model assessment (HOMA) was calculated as an indicator of insulin resistance.

RESULTS

When analyzing percentile values of insulin, HOMA and FFA by sex, we observed that girls had significantly higher insulin concentrations than boys (except at the 10th percentile) and significantly higher FFA (except at the 90th percentile) with no significant differences between sexes for HOMA. Multivariate regression analyses showed that insulin was positively associated with glucose, triglycerides and apoB in boys but not in girls, and negatively associated with FFA in both genders.

CONCLUSIONS

We report here data about the distribution of insulin in the Spanish prepubertal population. The higher levels of insulin in prepubertal girls could indicate that girls start to be more insulin resistant than boys at this age, although other manifestations of insulin resistance are not yet detectable.

Association of socioeconomic position with insulin resistance among children from Denmark, Estonia, and Portugal: cross sectional study

OBJECTIVES

To examine the association between socioeconomic position and insulin resistance in children from three countries in northern Europe (Denmark), eastern Europe (Estonia), and southern Europe (Portugal) that have different physical, economic, and cultural environments.

DESIGN

Cross sectional study.

PARTICIPANTS

3189 randomly selected schoolchildren aged 9 and 15 years from Denmark (n = 933), Estonia (n = 1103), and Portugal (n = 1153).

MAIN OUTCOME MEASURE

Insulin resistance (homoeostasis model assessment).

RESULTS

Family income and parental education were inversely associated with insulin resistance in Danish children but were positively associated with insulin resistance in Estonian and Portuguese children. Among Danish children, insulin resistance was 24% lower (95% confidence interval -38% to -10%) in those whose fathers had the most education compared with those with the least education. The equivalent results were 15% (2% to 28%) higher for Estonia and 19% (2% to 36%) higher for Portugal. These associations remained after adjustment for a range of covariates: -20% (-36% to -5%) for Denmark, 10% (-4% to 24%) for Estonia, and 18% (-1% to 31%) for Portugal. Strong statistical evidence supported differences between the associations in Denmark and those in the other two countries in both unadjusted and adjusted models (all P < 0.03).

CONCLUSIONS

Among Danish children, those with the most educated and highest earning parents had least insulin resistance, whereas the opposite was true for children from Estonia and Portugal.