Levothyroxine treatment restored the decreased circulating fibroblast growth factor 21 levels in patients with hypothyroidism

• FGF21 is an important endogenous regulator for energy metabolism.
• Hypothyroid patients had reduced plasma FGF21 levels.
• Levothyroxine treatment restored the decreased FGF21 levels in hypothyroid patients.

Background and aimsFibroblast growth factor 21 (FGF21) is an important endogenous regulator of energy metabolism. Thyroid hormone has been shown to regulate hepatic FGF21 expression in rodents. The goal of this study was to evaluate the plasma FGF21 levels in participants with normal thyroid function, subclinical hypothyroidism, or overt hypothyroidism and to investigate the change of plasma FGF21 levels in patients with overt hypothyroidism after levothyroxine treatment.MethodsA total of 473 drug-naive participants were recruited, including 250 healthy control subjects, 116 patients with subclinical hypothyroidism, and 107 patients with overt hypothyroidism. Thirty-eight patients with overt hypothyroidism were assigned to receive levothyroxine treatment.ResultsThe overt hypothyroidism group had decreased FGF21 levels compared with the control and subclinical hypothyroidism groups (P < 0.01). Levothyroxine treatment markedly attenuated the increased circulating levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), high-sensitivity C-reactive protein (hsCRP), and homeostasis model assessment index of insulin resistance (HOMA-IR) in patients with overt hypothyroidism. A significant increase in plasma FGF21 levels was observed after levothyroxine treatment (P < 0.01). The change in FGF21 levels was correlated with the increase of FT3 and FT4 after levothyroxine treatment (FT3: r = 0.44; FT4: r = 0.53; all P < 0.05).ConclusionsLevothyroxine treatment ameliorated metabolic disorders and restored the decreased circulating FGF21 levels in patients with overt hypothyroidism. The increase in FGF21 levels after levothyroxine treatment might be partly associated with the amelioration of metabolic disorders in patients with hypothyroidism.