For sarcopenia, both Sharp score (OR = 1.008, 95% CI 1.002–1.014; P = 0.013) and elevated myostatin levels (OR = 1.222, 95% CI 1.015–1.472; P = 0.034) were significant risk predictors, whereas higher irisin levels conferred protection (OR = 0.963, 95% CI 0.936–0.990; P = 0.007). Here, FNDC5 is linked to sarcopenia.