Effects of puberty and diabetes on metabolism of insulin-sensitive fuels

Puberty Is Associated with a Rising Hemoglobin A1c, Even in Youth with Normal Weight

Our objective was to explore the longitudinal trajectory of hemoglobin A1c (HbA1c) in well-characterized youth (n = 84) with normal weight and obesity during puberty. HbA1c rose from early puberty to Tanner stage 5, even in healthy, normal weight youth, revealing important implications for defining normal glycemia and prediabetes in adolescents.

Effect of growth hormone on insulin signaling

Growth hormone (GH) is a pleiotropic hormone that coordinates an array of physiological processes, including effects on bone, muscle, and fat, ultimately resulting in growth. Metabolically, GH promotes anabolic action in most tissues except adipose, where its catabolic action causes the breakdown of stored triglycerides into free fatty acids (FFA). GH antagonizes insulin action via various molecular pathways. Chronic GH secretion suppresses the anti-lipolytic action of insulin and increases FFA flux into the systemic circulation; thus, promoting lipotoxicity, which causes pathophysiological problems, including insulin resistance. In this review, we will provide an update on GH-stimulated adipose lipolysis and its consequences on insulin signaling in liver, skeletal muscle, and adipose tissue. Furthermore, we will discuss the mechanisms that contribute to the diabetogenic action of GH.

Cross-Sectional and Longitudinal Examination of Insulin Sensitivity and Secretion across Puberty among Non-Hispanic Black and White Children

BACKGROUND

Few studies using criterion measures of insulin sensitivity (SI) and insulin secretory capacity (ISC) have been conducted across puberty to adulthood. We examined how SI and ISC change from pre-puberty through adulthood.

METHODS

Hyperglycemic clamp studies were performed in a convenience sample of non-Hispanic Black (NHB) and White children evaluated at age 6 to 12 years and at approximately 5-year intervals into adulthood (maximum age 27 years). SI and ISC (first-phase and steady-state insulin secretion) were determined cross-sectionally in 133 unique participants across puberty and in adulthood. Additionally, longitudinal changes in SI and ISC were compared at two timepoints among three groups defined by changes in pubertal development: pre-pubertal at baseline and late-pubertal at follow-up (n=27), early-pubertal at baseline and late-pubertal at follow-up (n=27), and late-pubertal at baseline and adult at follow-up (n=24).

RESULTS

Cross-sectionally, SI was highest in pre-puberty and early puberty and lowest in mid-puberty (analysis of covariance [ANCOVA] P=0.001). Longitudinally, SI decreased from pre-puberty to late puberty (P<0.001), then increased somewhat from late puberty to adulthood. Cross-sectionally, first-phase and steady-state ISC increased during puberty and decreased in adulthood (ANCOVA P<0.02). Longitudinally, steady-state and first-phase ISC increased from pre-puberty to late puberty (P<0.007), and steady-state ISC decreased from late puberty to adulthood. The NHB group had lower SI (P=0.003) and greater first-phase and steady-state ISC (P≤0.001), independent of pubertal development.

CONCLUSION

This study confirms that SI decreases and ISC increases transiently during puberty and shows that these changes largely resolve in adulthood.

Does oral glutamine improve insulin sensitivity in adolescents with type 1 diabetes?

OBJECTIVE

The decline in insulin sensitivity (S_I) associated with puberty increases the difficulty of achieving glycemic control in adolescents with type 1 diabetes (T1D). The aim of this study was to determine whether glutamine supplementation affects blood glucose by enhancing S_I in adolescents with T1D.

METHODS

Thirteen adolescents with T1D (HbA1C 8.2 ± 0.1%) were admitted to perform afternoon exercise (four 15-min treadmill/5-min rest cycles of exercise) on two occasions within a 4-wk period. They were randomized to receive a drink containing either glutamine (0.25 g/kg) or placebo before exercise, at bedtime, and early morning in a double-blind, crossover design. Blood glucose was monitored overnight, and a hyperinsulinemic-euglycemic clamp was performed the following morning.

RESULTS

Blood glucose concentration dropped comparably during exercise on both days. However, the total number of nocturnal hypoglycemic events (17 versus 7, P = 0.045) and the cumulative probability of overnight hypoglycemia (50% versus 33%, P = 0.02) were higher on the glutamine day than on the placebo day. During clamp, glucose infusion rate was not affected by glutamine supplementation (7.7 ± 1 mg • kg^-1 • min^-1 versus 7.0 ± 1; glutamine versus placebo; P = 0.4).

CONCLUSIONS

Oral glutamine supplementation decreases blood glucose in adolescents with T1D after exercise. Insulin sensitivity, however, was unaltered during the euglycemic clamp. Although the mechanisms involved remain to be elucidated, studies to explore the potential use of glutamine to improve blood glucose control are needed.

Metabolic syndrome burden in apparently healthy adolescents is adversely associated with cardiac autonomic modulation--Penn State Children Cohort

BACKGROUND

Reduced cardiac autonomic modulation (CAM) has been associated with metabolic syndrome (MetS) in adults. However, the association between MetS component cluster and CAM has not been examined in adolescents.

METHODS

We conducted a cross-sectional analysis using data from the Penn State Child Cohort follow-up examination. CAM was assessed by heart rate variability (HRV) analysis of 39-h RR intervals, including frequency (high frequency, HF; low frequency, LF; and LF/HF ratio) and time (SDNN, standard deviation of all RR intervals; RMSSD, square root of the mean of the sum of the squares of differences between adjacent RR intervals; and HR, heart rate) domain variables. To assess the MetS burden, we used continuous MetS score (cMetS)--sum of the age and sex-adjusted standardized residual (Z-score) of five established MetS components. Linear mixed-effect models were used to analyze the association between cMetS and CAM in the entire population and stratified by gender.

RESULTS

After adjusting for age, sex, and race, cMetS was significantly associated with reduced HRV and higher HR. With 1 standard deviation increase in cMetS, there was a significant decrease in HF (-0.10 (SE = 0.02)), LF (-0.07 (SE = 0.01)), SDNN (-1.97 (SE = 0.50)), and RMSSD (-1.70 (SE = 0.72)), and increase in LF/HF (0.08 (SE = 0.02)) and HR (1.40 (SE = 0.26)). All cMetS components, with the exception of high-density lipoprotein (HDL), were associated with significantly decreased HRV and increased HR. High blood pressure (MAP) and triglyceride (TG) levels were also associated with an increase in LF/HF and decrease in RMSSD. An increase in high-density lipoprotein was only associated with higher LF and SDNN. Moreover, cMetS and HRV associations were more pronounced in males than in females. The associations between HRV and. MAP, TG, and HDL were more pronounced in females.

CONCLUSIONS

cMetS score is associated with lower HRV, suggesting an adverse impact on CAM, even in apparently healthy adolescents.

Nutrition and pubertal development

Nutrition is one of the most important factors affecting pubertal development. Puberty entails a progressive nonlinear process starting from prepubescent to full sexual maturity through the interaction and cooperation of biological, physical, and psychological changes. Consuming an adequate and balanced healthy diet during all phases of growth (infancy, childhood and puberty) appears necessary both for proper growth and normal pubertal development. Girls begin puberty at an earlier age compared to past decades. Excessive eating of many processed, high-fat foods, may be the cause of this phenomenon. Overweight or obese children are more likely to enter puberty early. Some evidence suggests that obesity can accelerate the onset of puberty in girls and may delay the onset of puberty in boys. Moreover, the progression of puberty is affected by nutrition. On the other hand, puberty triggers a growth spurt, which increases nutritional needs including macro and micronutrients. Increased caloric, protein, iron, calcium, zinc and folate needs have to be provided during this critical period of rapid growth. Severe primary or secondary malnutrition also can delay the onset and progression of puberty. The higher incidence of anorexia nervosa and bulimia in adolescents imposes a nutritional risk on pubertal development. Moreover, many environmental endocrine disruptors (EDs) have been identified that can significantly impair the normal course of puberty. This mini-review sums up some important findings in this important complex that link nutrition and pubertal development.

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.

Insulin resistance determined by Homeostasis Model Assessment (HOMA) and associations with metabolic syndrome among Chinese children and teenagers

OBJECTIVE

The aim of this study is to assess the association between the degree of insulin resistance and the different components of the metabolic syndrome among Chinese children and adolescents. Moreover, to determine the cut-off values for homeostasis model assessment of insulin resistance (HOMA-IR) at MS risk.

METHODS

3203 Chinese children aged 6 to 18 years were recruited. Anthropometric and biochemical parameters were measured. Metabolic syndrome (MS) was identified by a modified Adult Treatment Panel III (ATP III) definition. HOMA-IR index was calculated and the normal reference ranges were defined from the healthy participants. Receiver operating characteristic (ROC) analysis was used to find the optimal cutoff of HOMA-IR for diagnosis of MS.

RESULTS

With the increase of insulin resistance (quintile of HOMA-IR value), the ORs of suffering MS or its related components were significantly increased. Participants in the highest quintile of HOMA-IR were about 60 times more likely to be classified with metabolic syndrome than those in the lowest quintile group. Similarly, the mean values of insulin and HOMA-IR increased with the number of MS components. The present HOMA-IR cutoff point corresponding to the 95th percentile of our healthy reference children was 3.0 for whole participants, 2.6 for children in prepubertal stage and 3.2 in pubertal period, respectively. The optimal point for diagnosis of MS was 2.3 in total participants, 1.7 in prepubertal children and 2.6 in pubertal adolescents, respectively, by ROC curve, which yielded high sensitivity and moderate specificity for a screening test. According to HOMA-IR > 3.0, the prevalence of insulin resistance in obese or MS children were 44.3% and 61.6% respectively.

CONCLUSIONS

Our data indicates insulin resistance is common among Chinese obese children and adolescents, and is strongly related to MS risk, therefore requiring consideration early in life. As a reliable measure of insulin resistance and assessment of MS risk, the optimal HOMA-IR cut-off points in this cohort were developed with variation regarding puberty. HOMA-IR may be useful for early evaluating insulin resistance in children and teenagers and could have a long-term benefit of preventive and diagnostic therapeutic intervention.

Impact of pubertal development on endothelial function and arterial elasticity

OBJECTIVES

Little is known about the relation of pubertal development on endothelial function and arterial elasticity in children and adolescents; therefore, we compared brachial artery flow-mediated dilation and carotid artery elasticity across Tanner (pubertal) stages in children and adolescents.

STUDY DESIGN

Blood pressure, fasting lipids, glucose and insulin, body fat, insulin sensitivity adjusted for lean body mass, brachial flow-mediated dilation (percent dilation and area under the curve), endothelium-independent dilation (peak dilation and area under the curve), and carotid artery elasticity were evaluated across pubertal stages (Tanner I vs Tanner II-IV vs Tanner V) in 344 children and adolescents (184 males, 160 females; ages 6 to 21 years).

RESULTS

One hundred twenty-four subjects (mean age 8.23 ± 0.15 years; 52 females) were Tanner stage I; 105 subjects (mean age 13.19 ± 0.17 years; 47 females) were Tanner stages II-IV; and 115 subjects (mean age 17.19 ± 0.16 years; 61 females) were Tanner stage V. There were no significant differences for any of the measures of vascular structure and function across pubertal stages.

CONCLUSION

Results of the current study indicate that smooth-muscle and endothelial function, as well as carotid artery elasticity, do not differ throughout pubertal development and that accounting for pubertal stage when reporting vascular data in children and adolescents may be unnecessary.

Obesity, metabolic syndrome, and insulin resistance in urban high school students of minority race/ethnicity

OBJECTIVES

To determine the point prevalences of metabolic syndrome (MetS) and its components among healthy weight, overweight, and obese inner-city public high school students, to compare the prevalences of MetS when using 2 different definitions (one with the impaired fasting glucose [IFG] level and the other with a homeostasis model assessment of insulin resistance [HOMA-IR] of 3.99 or higher to define the glucose regulation component), and to compare the degree to which HOMA-IR and fasting glucose level are associated with the other MetS components.

DESIGN

Cross-sectional analysis.

SETTING

Two New York City public high schools, from April 2008 through August 2011.

PARTICIPANTS

Convenience sample of 1185 high school youth, comprising predominantly Hispanic and African American students from low-income households, participating in The Banishing Obesity and Diabetes in Youth Project, a medical screening and education program.

MAIN OUTCOME MEASURES

Prevalences of the following individual MetS components: IFG threshold, HOMA-IR, hypertension, central adiposity, hypertriglyceridemia, and low high-density lipoprotein cholesterol. Rates of MetSIFG and MetSHOMA-IR were also assessed.

RESULTS

MetSIFG and MetSHOMA-IR point prevalences were both 0.3% in the healthy weight group; they were 2.6% and 5.9%, respectively, in the overweight group and were 22.9% and 35.1%, respectively, in the obese group (P < .05 for both). An IFG threshold of 100 mg/dL or higher was found in 1.0% of participants, whereas a HOMA-IR of 3.99 or higher was found in 19.5% of participants.

CONCLUSIONS

An elevated HOMA-IR is much more sensitive than an IFG threshold in identifying adolescents with metabolic dysregulation. Using a HOMA-IR threshold of 3.99 identifies more youth with MetS than using an IFG threshold of 100 mg/dL. In addition to increasing the sensitivity of MetS detection, HOMA-IR has a much higher association with the other MetS components than the IFG threshold and may better reflect a unified underlying pathologic process useful to identify youth at risk for disease.

Impaired growth and force production in skeletal muscles of young partially pancreatectomized rats: a model of adolescent type 1 diabetic myopathy?

This present study investigated the temporal effects of type 1 diabetes mellitus (T1DM) on adolescent skeletal muscle growth, morphology and contractile properties using a 90% partial pancreatecomy (Px) model of the disease. Four week-old male Sprague-Dawley rats were randomly assigned to Px (n = 25) or Sham (n = 24) surgery groups and euthanized at 4 or 8 weeks following an in situ assessment of muscle force production. Compared to Shams, Px were hyperglycemic (>15 mM) and displayed attenuated body mass gains by days 2 and 4, respectively (both P<0.05). Absolute maximal force production of the gastrocnemius plantaris soleus complex (GPS) was 30% and 50% lower in Px vs. Shams at 4 and 8 weeks, respectively (P<0.01). GP mass was 35% lower in Px vs Shams at 4 weeks (1.24±0.06 g vs. 1.93±0.03 g, P<0.05) and 45% lower at 8 weeks (1.57±0.12 vs. 2.80±0.06, P<0.05). GP fiber area was 15–20% lower in Px vs. Shams at 4 weeks in all fiber types. At 8 weeks, GP type I and II fiber areas were ∼25% and 40% less, respectively, in Px vs. Shams (group by fiber type interactions, P<0.05). Phosphorylation states of 4E-BP1 and S6K1 following leucine gavage increased 2.0- and 3.5-fold, respectively, in Shams but not in Px. Px rats also had impaired rates of muscle protein synthesis in the basal state and in response to gavage. Taken together, these data indicate that exposure of growing skeletal muscle to uncontrolled T1DM significantly impairs muscle growth and function largely as a result of impaired protein synthesis in type II fibers.

Insulin resistance in obese children and adolescents: HOMA-IR cut-off levels in the prepubertal and pubertal periods

OBJECTIVE

Childhood obesity is associated with an increased risk for insulin resistance. The underlying mechanism for the physiological increase in insulin levels in puberty is not clearly understood. The aim of the present study was to determine the cut-off values for homeostasis model assessment for insulin resistance (HOMA-IR) in obese children and adolescents according to gender and pubertal status.

METHODS

Two hundred and eight obese children and adolescents (141 girls, 127 boys) aged between 5 and 18 years were included in the study. The children were divided into prepubertal and pubertal groups. A standard oral glucose tolerance test (OGTT) was carried out in all children. A total insulin level exceeding 300 μU/mL in the blood samples, collected during the test period, was taken as the insulin resistance criterion. Cut-off values for HOMA-IR were calculated by receiver operating characteristic (ROC) analysis.

RESULTS

In the prepubertal period, the rate of insulin resistance was found to be 37% in boys and 27.8% in girls,while in the pubertal period, this rate was 61.7% in boys and 66.7% in girls. HOMA-IR cut-off values for insulin resistance in the prepubertal period were calculated to be 2.67 (sensitivity 88.2%, specificity 65.5%) in boys and 2.22 (sensitivity 100%, specificity 42.3%) in girls, and in the pubertal period, they were 5.22 (sensitivity 56%, specificity 93.3%) in boys and 3.82 (sensitivity 77.1%, specificity 71.4%) in girls.

CONCLUSIONS

Since gender, obesity and pubertal status are factors affecting insulin resistance, cut-off values which depend on gender and pubertal status, should be used in evaluation of insulin resistance.

The role of PAS kinase in PASsing the glucose signal

PAS kinase is an evolutionarily conserved nutrient responsive protein kinase that regulates glucose homeostasis. Mammalian PAS kinase is activated by glucose in pancreatic beta cells, and knockout mice are protected from obesity, liver triglyceride accumulation, and insulin resistance when fed a high-fat diet. Yeast PAS kinase is regulated by both carbon source and cell integrity stress and stimulates the partitioning of glucose toward structural carbohydrate biosynthesis. In our current model for PAS kinase regulation, a small molecule metabolite binds the sensory PAS domain and activates the enzyme. Although bona fide PAS kinase substrates are scarce, in vitro substrate searches provide putative targets for exploration.

Metformin added to insulin therapy for type 1 diabetes mellitus in adolescents

BACKGROUND

In adolescents with type 1 diabetes, insulin resistance likely plays a role in the deterioration of metabolic control. In type 1 diabetes, addition of metformin to insulin therapy, to improve insulin sensitivity, has been assessed in a few trials involving few patients or in uncontrolled studies of short duration. No systematic reviews are available up to date to summarize the evidence about metformin addition to insulin therapy in adolescents with type 1 diabetes.

OBJECTIVES

To assess the effects of metformin added to insulin therapy for type 1 diabetes mellitus in adolescents.

SEARCH STRATEGY

We searched The Cochrane Library, MEDLINE and EMBASE. We also searched databases of ongoing trials, reference lists of relevant reviews, and we contacted experts, authors and manufacturers.

SELECTION CRITERIA

Any randomised controlled trial (RCT) of at least three months duration of treatment comparing metformin added to insulin therapy versus insulin therapy alone in adolescents with type 1 diabetes was included. Cross-over and quasi-randomised controlled trials were excluded.

DATA COLLECTION AND ANALYSIS

Two reviewers read all abstracts, assessed quality and extracted data independently. Authors were contacted for missing data.

MAIN RESULTS

Only two trials (60 participants) investigating the effect of metformin added to insulin therapy for three months in adolescents with poorly controlled type 1 diabetes could be included. Meta-analysis was not possible due to the clinical and methodological heterogeneity of data. Both studies suggested that metformin treatment lowered glycosylated haemoglobin A1c (HbA1c) in adolescents with type 1 diabetes and poor metabolic control. Improvements in insulin sensitivity, body composition or serum lipids were not documented in either study, however, one study showed a decrease in insulin dosage by 10%. Adverse effects were mainly gastrointestinal in both studies and hypoglycaemia in one study. No data on health-related quality of life, all-cause mortality or morbidity are currently available.

AUTHORS' CONCLUSIONS

There is some evidence suggesting improvement of metabolic control in poorly controlled adolescents with type 1 diabetes, on addition of metformin to insulin therapy. Stronger evidence is required from larger studies, carried out over longer time periods to document the long-term effects on metabolic control, health-related quality of life as well as morbidity and mortality in those patients.

Prevalence and determinants of insulin resistance among U.S. adolescents: a population-based study

OBJECTIVE

We sought to examine the distribution of insulin and homeostasis model assessment of insulin resistance (HOMA-IR) and associations of HOMA-IR with sex, race/ethnicity, age, and weight status, as measured by BMI, among U.S. adolescents.

RESEARCH DESIGN AND METHODS

Of 4,902 adolescents aged 12-19 years who participated in the National Health and Nutrition Examination Survey 1999-2002, analysis was performed for a nationally representative subsample of 1,802 adolescents without diabetes who had fasting laboratory measurements. The main outcome measure was HOMA-IR, calculated from fasting insulin and glucose and log transformed for multiple linear regression analyses.

RESULTS

In adjusted regression models that included age and weight status, girls had higher HOMA-IR than boys and Mexican-American children had higher HOMA-IR levels than white children. There were no significant differences in adjusted HOMA-IR between black and white children. Obese children (BMI >/=95th percentile) had significantly higher levels of HOMA-IR compared with children of normal weight (BMI <85th percentile) in adjusted comparisons (mean HOMA-IR 4.93 [95% CI 4.56-5.35] vs. 2.30 [2.21-2.39], respectively). Weight status was by far the most important determinant of insulin resistance, accounting for 29.1% of the variance in HOMA-IR. The prevalence of insulin resistance in obese adolescents was 52.1% (95% CI 44.5-59.8).

CONCLUSIONS

Obesity in U.S. adolescents represents the most important risk factor for insulin resistance, independent of sex, age, or race/ethnicity. The prevalence of insulin resistance in obese children foreshadows a worrisome trend for the burden of type 2 diabetes in the U.S.

Insulin resistance and whole body energy homeostasis in obese adolescents with fatty liver disease

Obese adolescents are at risk of developing NAFLD and type 2 diabetes. We measured noninvasively the IHF content of obese adolescents to ascertain whether it is associated with insulin resistance and abnormal energy homeostasis. IHF content, whole body energy homeostasis, insulin sensitivity, and body composition were measured using localized hepatic (1)H-MRS, indirect calorimetry, fasting-derived and 3-h-OGTT-derived surrogate indexes (HOMA2 and WBISI), and DEXA, respectively, in 54 obese adolescents (24 female and 30 male, age 13 +/- 2 yr, BMI >99th percentile for their age and sex). NAFLD (defined as IHF content >5% wet weight) was found in 16 individuals (30%) in association with higher ALT (P < 0.006), Hb A(1c) (P = 0.021), trunk fat content (P < 0.03), and lower HDL cholesterol (P < 0.05). Individuals with NAFLD had higher fasting plasma glucose (89 +/- 8 vs. 83 +/- 9 mg/dl, P = 0.01) and impaired insulin sensitivity (HOMA2 and WBISI, P < 0.05). Meanwhile, parameters of insulin secretion were unaffected. Their reliance on fat oxidation in the fasting state was lower (RQ 0.83 +/- 0.08 vs. 0.77 +/- 0.05, P < 0.01), and their ability to suppress it during the oral glucose challenge was impaired (P < 0.05) vs. those with normal IHF content. When controlling for trunk fat content, the correlation between IHF content and insulin sensitivity was weakened, whereas the correlation with fasting lipid oxidation was maintained. In conclusion, NAFLD is common in childhood obesity, and insulin resistance is present in association with increased trunk fat content. In contrast, the rearrangement of whole body substrate oxidation in these youngsters appeared to be an independent feature.

Insulin resistance in children and adolescents

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

Longitudinal study on pubertal insulin resistance

Previous cross-sectional studies show that puberty is associated with a reduction in insulin sensitivity (S(I)), but no longitudinal studies have examined this change in detail. This study is a longitudinal study in 60 children (33 male and 27 female subjects; 32 Caucasian and 28 African-American) examined at Tanner stage I (age 9.2 +/- 1.4 years) and after 2.0 +/- 0.6 years of follow-up, by which time 29 children remained at Tanner stage I and 31 had progressed to Tanner stage III or IV. Tanner stage was assessed by physical examination. S(I), the acute insulin response (AIR), and the disposition index (DI) were determined by the tolbutamide-modified intravenous glucose tolerance test and minimal modeling, body fat mass was assessed by dual-energy X-ray absorptiometry, visceral fat was determined by computed tomography, and fasting blood was analyzed for hormone levels. In children progressing to Tanner stage III, S(I) fell significantly by 32% (4.4 +/- 3.0 to 3.0 +/- 1.7 x 10(-4)min(-1)/[microIU/ml]), AIR increased by 30%, DI fell by 27%, and there was a significant increase in fasting glucose (93.5 +/- 5.0 to 97.0 +/- 4.1 mg/dl) and insulin (14.3 +/- 8.1 to 18.6 +/- 11.0 microIU/ml). In children remaining at Tanner stage I, there was a slight increase in S(I) (6.4 +/- 3.1 to 7.4 +/- 3.5 x 10(-4)min(-1)/[microIU/ml]) with no significant change in AIR or fasting glucose and insulin. The pubertal fall in S(I) was more consistent in African-Americans; remained significant after controlling for age, sex, and change in fat mass, visceral fat, and fat-free mass; and was similar in children at low, medium, and high body fat. Change in S(I) was not significantly related to change in fasting hormone levels, but change in AIR was significantly related to change in androstendione (r = 0.39; P = 0.04). Pubertal transition from Tanner stage I to Tanner stage III was associated with a 32% reduction in S(I,) and increases in fasting glucose, insulin, and AIR. These changes were similar across sex, ethnicity, and obesity. The significant fall in DI suggests conservation in beta-cell function or an inadequate beta-cell response to the fall in S(I). The fall in S(I) was not associated with changes in body fat, visceral fat, IGF-I, androgens, or estradiol.