We examined 1010 children and adolescents, referred to our ward (Childhood Obesity Service, Department of Paediatrics, Second University of Naples) for obesity between 1999 and 2008. Subjects with known presence of diabetes or using medications altering blood pressure, glucose or lipid metabolism, with goitre or known thyroid disease were excluded (1 subject with type 2 diabetes, 9 with autoimmune thyroiditis). The ethical committee of the Second University of Study of Naples approved the study. Informed consent was obtained by parents and, where appropriate, by children.
Of the 1010 subjects enrolled, 485 were girls. Obesity was defined according to the body mass index (BMI) 95th percentile for age and sex using the definition of the International Task Force for Obesity in Childhood and the charts for Italian population [9]. Obesity degree was evaluated using the z-score BMI, calculated with the LMS method [10].
Anthropometric measures were assessed at the time of the first visit and in a subgroup of patients with TSH elevation after 6 months.
Waist circumference was measured by the same operator to the nearest centimetre with a flexible steel tape measure while the subjects were standing, after gently exhaling, as the minimal circumference measurable on the horizontal plane between the lowest portion of the rib cage and iliac crest. The intra-operator coefficient of variation was 1,3%.
Standard deviation (SD) scores for waist circumference have been calculated using normative values for Italian population [11].
Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured three times while the subjects were seated, and the two last measurements were averaged for the analysis and we calculated SD according to normative values [12].
The pubertal stage was assessed using Tanner criteria [13].
After an overnight fasting, blood sample were obtained for triglycerides, high density lipoprotein (HDL) cholesterol, insulin, serum glucose, thyroid hormones (TSH, fT3, fT4) and anti-tyreoglobulin (Tg-Ab) and anti-peroxidase anti-bodies (TPO-Ab).
Serum fasting glucose levels were measured with glucose oxidase method. Triglycerides and HDL cholesterol were measured by an Olympus AU 560 apparatus using an enzymatic colorimetric method.
Immunoreactive insulin was assayed by IMX (Abbott Diagnostics, Santa Clara, CA). The mean intra- and inter-assay coefficients of variations were 4.7% and 7.2%, respectively. The degree of insulin resistance was determined using a homeostasis model assessment (HOMA), [insulin (mU/L) × glucose level(mmol/L)/22.5] [14].
Thyroid hormones (TSH, fT3, and fT4) and TPO-Ab and Tg-Ab were determined by high-specific solid-phase technique-chemiluminescenceimmunoassays (Perkinelmer, Turku, Finland).
In a subgroup of 160 children we measured leptin plasma levels using double-antibody radioimmunoassay (Human Leptin RIA KIT, Linco-Research, St. Charles, MO). The sensitivity cut-off for the leptin assay was 0.5 ng/ml; the intra and inter-assay variation coefficients were 10.8% and 7%, respectively.
TPO-Ab and Tg-Ab levels higher than 60 UI/ml were considered positive, and autoimmune thyroiditis was diagnosed.
Isolated hyperthyrotropinemia was diagnosed when TSH was higher than 4.2 μUI/ml (97,5th for our assay), with normal fT3 and fT4 and no signs or symptoms of hypothyroidism.
All patients were submitted to a weight loss program. They consumed a nutritionally balanced (50% carbohydrate, 30% fat and 20% protein) self-selected diet of common foods (80% of the recommended dietary energy allowances for age and sex). All subjects underwent a lifestyle modification program. They followed a program based on physical exercise, and behavioral therapy, including individual psychological care of the child and his or her family. Thyroid hormones and lipids were reassessed after 6 months of the weight reduction program in patients with elevated TSH levels. Weight reduction was considered as at least a 0.5 decrease in BMI z-score [15].
All values are expressed as mean ± SD. Skewness and kurtosis tests were used to evaluate the normal distribution of the variables. The significance of changes in discrete variables was analyzed by the X2 test.
Mean differences were analyzed with one-way ANOVA for variables with a normal distribution, and with the Kruskal-walis test for variables with non Gaussian distribution. Obese children with isolated hyperthyrotropinemia, were compared to the obese children with normal TSH concentrations with respect to peripheral hormones, lipids, HOMA-index, blood pressure and anthropometric measures, and in a subgroup to leptin.
In the patients with hyperthyrotropinemia independent samples t-test for normal distribution and Mann-Whitney test for parameters with non-Gaussian distribution were used to compare the changes in the outcome variables between the group with decrease in BMI z-score >0.5 point, the one with decrease in BMI z-score between 0.2 and 0.5 points and the group with no changes in BMI z-score.
Linear regression model has been performed to investigate the correlation between TSH and BMI z-score, waist, lipids, blood pressure and HOMA index (and leptin in the subgroup in which it was tested).
Multiple linear regression analyses with lipids or blood pressure as dependent variables and age, gender, degree of overweight (BMI z-score) pubertal stage, HOMA index, and thyroid hormones as independent variables were performed.
Gender and pubertal stage were used as classified variables. A P < 0.05 was considered statistically significant. Stat-Graph 3.0 software for Windows was used for the statistical analysis.
