Background: Irisin, an exercise-induced myokine and adiponectin, an adipocyte-derived hormone, are involved in energy metabolism and musculoskeletal health. However, their associations with obesity, abdominal obesity, sarcopenia and sarcopenic obesity remain unclear, and longitudinal evidence is limited. This study investigated the cross-sectional and longitudinal associations of these biomarkers with obesity- and sarcopenia-related outcomes.

Methods: We used data from the Hallym Aging Study, a cohort of Korean adults aged ≥ 45 years (45-64 years: 30%, ≥65 years: 70%). The cross-sectional analysis used the third wave (2010), while the longitudinal analysis included the second (2007, baseline) and third waves. In both analyses, sex-specific tertile groups (T1, T2 and T3) were defined based on baseline levels and changes in irisin and adiponectin over 3 years. Lean soft tissue and fat mass were assessed using dual-energy x-ray absorptiometry. Obesity was defined as body fat percentages > 29.7% for males and > 37.2% for females. For individuals without obesity, low ALST was defined as appendicular lean soft tissue (ALST)/height2 < 7.0 kg/m2 for males and < 5.4 kg/m2 for females. For individuals with obesity, low ALST was defined as an ALST/body weight < 26.8% for males and < 21.0% for females. Multivariable logistic regression was performed to examine the associations between circulating irisin and adiponectin and obesity- and sarcopenia-related outcomes.

Results: A total of 357 and 360 participants were included in the cross-sectional analyses of irisin and adiponectin, respectively, and 351 were included in the longitudinal analysis (baseline 2007; median age: 70 years; 54% female). In cross-sectional analysis, irisin was not significantly associated with obesity- and sarcopenia-related outcomes after adjustment for confounding variables. Longitudinally, the greatest irisin increase group (T3) over 3 years had higher odds of obesity [odds ratio (OR) 2.39, 95% confidence interval (CI) 1.24-4.71], abdominal obesity (OR 2.19, 95% CI 1.04-4.72), sarcopenia (OR 2.11, 95% CI 1.14-3.97), sarcopenic obesity (OR 3.40, 95% CI 1.43-8.61) and low ALST (OR 2.21, 95% CI 1.24-3.99) at the follow-up than the T1 group. In contrast, adiponectin levels showed inverse associations with obesity (OR 0.47, 95% CI 0.24-0.93) and abdominal obesity (OR 0.48, 95% CI 0.25-0.90) only in cross-sectional analysis.

Conclusions: Despite irisin's proposed protective role against obesity and sarcopenia, our findings suggest that greater 3-year increases in irisin were associated with increased odds of obesity, abdominal obesity, sarcopenia and sarcopenic obesity at the follow-up. Conversely, adiponectin showed an inverse cross-sectional association with obesity and abdominal obesity.