Mediators of energy homeostasis in hyperthyroidism

OBJECTIVE: The aim of this study was to assess the effect of hyperthyroidism and its treatment on body weight and composition, insulin resistance, and mediators of appetite and energy homeostasis, namely ghrelin, leptin, adiponectin, and fibroblast growth factor 21 (FGF21). SUBJECTS AND METHODS: Thirty-five adult patients (27 female and 8 male, aged 39.63 ± 9.70 years) with overt hyperthyroidism were evaluated for leptin, ghrelin, adiponectin, and FGF21 levels; insulin resistance; and body composition using DEXA both at baseline and a minimum of two months following normalization of serum thyroxin on carbimazole treatment. Comparison of means between the baseline and post treatment values was performed by the paired t test for normally distributed parameters and by the Wilcoxon signed-rank test for non-normally distributed data. RESULTS: Hyperthyroidism correction resulted in an increase in weight from 51.15 ± 8.50 kg to 55.74 ± 8.74 kg (P < 0.001), paradoxically accompanied by a decrease in insulin resistance as measured by HOMA-IR from 1.35 (1.02-1.72) to 0.73 (0.52-0.93) ( P < 0.001). Correction of hyperthyroidism was also associated with a decrease in FGF21 from 58 (55-64) to 52 (47-58) pg/mL ( P < 0.001) and in leptin levels from 17 (7-36) to 11 (4.6-28) ng/mL ( P = 0.03). CONCLUSION: Despite lower body weight, thyrotoxicosis is associated with insulin resistance. High levels of thermogenic hormones, leptin, and FGF21 were observed in thyrotoxicosis and may be partly responsible for the excessive heat production typical of this condition.