Bidirectional longitudinal associations between estimated muscle mass and self-reported chronic lung disease in middle-aged and older adults: findings from the China health and retirement longitudinal study

The bidirectional relationship between muscle mass and chronic lung diseases (CLD) in middle-aged and older adults remains inadequately explored. This study aims to investigate the bidirectional association between estimated muscle mass and self-reported chronic lung diseases while elucidating the mediating mechanisms underlying this relationship. This study utilized data from the nationally representative China Health and Retirement Longitudinal Study (2011-2018), focusing on individuals aged 45 years or older. Cox regression was used to investigate the bidirectional relationship between estimated muscle mass and self-reported CLD. Causal mediation analysis was employed to evaluate the role of 16 blood biomarkers as potential mediators. Sensitivity analysis using cross-lagged models was conducted to verify the robustness of the bidirectional association between estimated muscle mass and self-reported CLD. Among 10,591 participants, 1,742 (16%) self-reported CLD during a median follow-up of 4.4 years. Participants with low estimated muscle mass had a 27% higher risk of developing self-reported CLD compared to those with normal muscle mass (HR = 1.27, 95% CI: 1.12-1.44). In a separate analysis of 6,067 participants, 708 (12%) experienced new-onset estimated low muscle mass, with those reporting CLD showing a 26% increased risk of muscle loss during a median follow-up of 2.5 years (HR = 1.26, 95% CI: 1.06-1.49). Notably, individuals with insufficient physical activity exhibited a significantly higher risk of self-reported CLD compared to those who engaged in regular exercise (HR = 1.91; 95% CI: 1.37-2.66). Additionally, the negative impact of low estimated muscle mass was more pronounced in male participants than in females (HR = 1.65; 95% CI: 1.33-2.03) over the same follow-up period. Causal mediation analysis suggested that cystatin C may mediate 0.61% of the association between estimated muscle mass and self-reported CLD. There is a bidirectional relationship between self-reported CLD and low estimated muscle mass. Self-reported CLD may cause varying degrees of estimated muscle mass reduction across different population subgroups. Understanding this dynamic and its variations can enhance prevention and treatment strategies for both conditions.