Introduction: Irisin, a cleaved and secreted part of the transmembrane protein FNDC5, is a recently discovered adipo-myokine that is said to have a significant influence on body metabolism. Changes in thyrometabolic state may also alter the serum irisin level. Since already reported data are not fully consistent, the aim of the present research is to evaluate the time-dependent changes in serum irisin level in patients affected by overt hypothyroidism.

Material and methods: The study involved 36 subjects — two groups of 12 patients with long-lasting (AITD) and short-term (TC) overt hypothyroidism, and a control group (CG) of 12 subjects, matched for age and gender. Serum irisin level, thyrometabolic state, creatine kinase (CK — muscle damage marker), glucose, and insulin concentration were assessed and compared between groups.

Results: The irisin level was significantly lower in AITD than in TC and CG (p = 0.02; p < 0.01; respectively) patients, with no statistical difference between TC and CG (p > 0.05). There was no significant difference between free triiodothyronine and free thyroxine levels in AITD and TC patients (p > 0.05). CK concentration was significantly higher in AITD than in CG patients (p < 0.01) with no difference between AITD and TC patients (p > 0.05) as well as TC and CG patients (p > 0.05). Additionally, the CK level negatively correlated with the irisin level (r = –0.58; p < 0.01).

Conclusions: In conclusion, the irisin concentration changes during thyroid function impairment may be time-dependent. Patients with prolonged hypothyroidism have lower irisin levels that those with short-term disorder. (Endokrynol Pol 2016; 67 (5): 476–480)