As shown in a similar study on Chinese middle-aged and older adults with CO and MetS, irisin levels were negatively associated with waist-to-hip ratio, and our findings were quite in line with this observation that albeit only tending to achieve statistical significance (P = 0.12), serum irisin levels were also negatively correlated with waist circumference (R = −0.15). The gene discussed is FNDC5; the disease is metabolic syndrome.