FNDC5 and chronic obstructive pulmonary disease: Nevertheless, investigations dealing with other populations showed comparable irisin levels: 26.3 (IQR: 22.6, 32.4) ng/ml, 53.7 (IQR: 46.7, 62.8) ng/ml, 58.5 (42.8, 78.9) ng/ml in smokers with and without COPD, and in non-smoking individuals, respectively (Kureya et al., 2016).