Thyroid function tests in obese prepubertal children: correlations with insulin sensitivity and body fat distribution

Background/Aims: Elevated thyroid-stimulating hormone (TSH) concentrations in association with normal/slightly elevated free triiodothyronine (fT(3)) and/or free thyroxine (fT(4)) have been consistently found in obese children. To examine relationships between adiposity, insulin sensitivity, and TSH, fT(3) and fT(4). Methods: 240 overweight/obese prepubertal children were studied. Fasting TSH, fT(3), fT(4), glucose, insulin, C-peptide, lipids, leptin and adiponectin were evaluated. Insulin sensitivity and resistance were estimated [quantitative insulin check index (QUICKI), insulin sensitivity index (ISI), and hepatic insulin resistance index]. Body fat was measured by dual-energy X-ray absorptiometry. The central obesity index was calculated as the ratio of fat tissue in the trunk region to fat tissue in the leg region. Results: The multiple regression analysis with age, gender and measures of fatness as covariates showed that QUICKI was the only significant negative predictor of TSH and central obesity index the strongest positive predictor of fT(3), in association with either age or hepatic insulin resistance index, and that the only positive determinant of fT(4) was hepatic insulin resistance index. Conclusions: Reduced insulin sensitivity is associated with augmented TSH and fT(4), while progressive central fat accumulation is strictly related to a parallel increase in fT(3) levels, independently from total body fat. Further studies are needed to understand mechanisms linking thyroid function to insulin sensitivity and body composition in obese children.