Relationship of thyroid function with body mass index and insulin-resistance in euthyroid obese subjects

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Abstract
Background and aims: It is recognized that overt thyroid dysfunction is associated with weight changes, but the influence of a minor alteration of thyroid function remains unclear. This study aimed to further investigate the relationship between obesity and thyroid function and to examine the possible role of insulin resistance on the hypothalamic-pituitary-thyroid axis. Methods and results: Serum TSH and free T4 (FT4) levels, anthropometric and metabolic parameters were evaluated in 581 obese patients. In all patients TSH values progressively increased according to the severity of obesity and were positively correlated with body mass index (p=0.001, r=0.13) and waist circumference (p=0.02, r=0.11). Patients with insulin resistance showed higher TSH (1.8±1.0 vs 1.6±0.9 μUI/l; p=0.03) and lower FT4 levels (13.8±2.3 vs 15.0±2.2 pmol/l; pppp4 was negatively associated with fasting insulin (pppConclusions: A relationship between thyroid function and overweight/obesity condition seems to exist, mainly influenced by insulin resistance. Whether variations in TSH and/or thyroid hormones, within a normal range, can influence body weight or whether obesity per se can alter thyroid function cannot be stated so far. Further studies are needed to assess the link between thyroid function and body weight, by considering not only changes in thyroid hormones, but also body fat distribution, obesity duration and low-grade inflammation.

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