Objective: Irisin, a newly discovered myokine, increases thermogenesis and energy consumption, especially after exercise. It has also been reported to stimulate the transformation of white fat cells into brown fat cells. Thus, it causes weight loss and increases the sensitivity to insulin. Nicotine affects the energy metabolism of the body through several mechanisms. Cigarette smokers are widely known to show decreased weight gain and increased weight loss. Since irisin and smoking/nicotine have similar effects on energy metabolism, this study proposed to determine the serum irisin levels in smokers. Material and Methods: Thirty-one healthy smokers aged 17-24 years and 31 agematched healthy non-smokers were included in this study. Serum irisin levels were determined using ELISA. Results: The smokers had been smoking for an average of 31±19 (2-84) months and smoked an average of 13.7±0.4 (5-25) cigarettes daily. The smokers had higher height and body weight and levels of serum creatinine and triglyceride and lower levels of HDL-C than non-smokers (p<0.05). Serum irisin levels and body mass index were not different between the two groups (p>0.05). The serum irisin level was correlated only with serum creatinine level in the entire group (r=-0.26, p<0.05). The serum irisin levels were not correlated with the duration and amount of cigarette smoking, as well as levels of serum glucose, insulin, total cholesterol, triglyceride, LDL-C, HDL-C, alanine aminotransferase, free T4, and TSH in the entire group (p>0.05). Conclusion: Serum irisin level in cigarette smokers is not different to that of non-smokers. It is not related to the duration and amount of cigarette smoking. Further prospective dose and time-controlled studies are needed to investigate whether similar effects of smoking/nicotine exposure on energy metabolism are related to irisin metabolism.

Keywords: Cigarette; smoking; irisin; body weight; body mass index