FNDC5 and hypothyroidism: Table 1 displays the clinical characteristics of all subjects. No difference was observed in HR and HDL-C levels between the two groups (Table 1). People with severe hypothyroidism had significantly higher BMI, TC, TG, LDL-C, CK, and TSH concentrations, while free T3 (FT3) and free T4 (FT4) levels were significantly reduced compared with controls (all P < 0.01). Of note, irisin concentrations were significantly lower in the severe hypothyroidism group than in controls (P=0.014).