Thyroid hormones in the pathogenesis and treatment of obesity

Thyroid hormones (TH) are potent modulators of adaptive thermogenesis and can potentially contribute to development of obesity. The decrease of T₃ in association with reduction of calorie intake is centrally regulated via decreases in leptin and melanocortin concentrations and peripherally via a decrease in deiodinase activity, all aimed at protein and energy sparing. The use of TH in the treatment of obesity is hardly justified except in cases of elevated thyrotropin (TSH) with low/normal T₃ and T₄ and/or a low T₃ or T′₃/T₄ or a high TSH/T₃ ratio. TH treatment with small doses of T₃ can also be exceptionally applied in obese patients resistant to dietary therapy who are taking β-adrenergic blockers or with obesity developed after cessation of cigarette smoking and with hyperlipidemia and a concomitant high thryrotropin/T₃ ratio. Supplementation with Se²⁺ and Zn²⁺ may be tried along with more severe calorie restriction to prevent decline of T₃.