Long-Term Determinants of Lean Mass in Ageing Adults: A 17-Year Longitudinal Cohort Study With Repeated Measures

OBJECTIVE: Age-related loss of lean mass is a hallmark of sarcopenia and a contributor to functional decline and morbidity in ageing populations. This study aimed to identify long-term determinants of lean mass during ageing. METHODS: Data from 3033 participants (ages 20-96 years; 49% women) in the Geelong Osteoporosis Study were analysed using linear mixed effect models with random intercepts. Appendicular lean mass (ALM) was derived from arm and leg lean mass measured using dual-energy X-ray absorptiometry. Time-varying covariates were included; missing data were imputed using predictive mean matching. RESULTS: Over 16.7 years (IQR 9.7-23.2), women and older participants had lower ALM (β = -8.36; 95% CI -8.58, -8.15; β = -0.07; 95% CI -0.08, -0.06). Higher ALM was associated with socio-economic status (0.33; 0.14, 0.51), dietary calcium intake (0.46; 0.20, 0.67), femoral neck BMD (0.38; 0.29, 0.47) and thyroid hormone therapy (0.52; 0.04, 0.99). Physical inactivity (-0.48; -0.65, -0.31), smoking (-0.24; -0.46, -0.06) and stroke history (-0.51; -0.96, -0.07) were associated with lower ALM. Non-linear associations were observed for follow-up duration (fu: β = -0.16; fu²: β = 0.01; -p < 0.001), body mass index (BMI: β = 0.55; BMI²: β = -0.00; p < 0.001), systolic blood pressure (SBP: β = 0.06; SBP²: β = -0.00; p < 0.001), serum C-terminal telopeptide of type I collagen (CTx: β = 0.14, p < 0.001; CTx²: β = -0.01, p = 0.03) and high-sensitivity Creactive protein (hsCRP: β = -10.38; hsCRP²: β = 11.70; -p < 0.001). In fat-mass-adjusted models, low-density lipoprotein cholesterol (0.14; 0.04, 0.24) and triglycerides (0.22; 0.11, 0.33) were positively associated with ALM, whereas high-density lipoprotein cholesterol (-0.53; -0.81, -0.25) was inversely associated with ALM. CONCLUSIONS: Sociodemographic, lifestyle, anthropometric, clinical, biochemical and treatment-related factors show independent associations with longitudinal changes in ALM.