Social isolation and lung function in middle-aged and older adults: identifying modifiable pathways across two...

Limited evidence exists on the relationship between social isolation and lung function, with few studies exploring underlying mechanisms. This study examined the association between social isolation and lung function decline, and the mediating roles of smoking, income, physical activity, and BMI in U.S. and Chinese populations.

This study utilized data from adults aged ≥ 45 years in NHANES (2007-2012, cross-sectional) and CHARLS (2011 and 2015, longitudinal). Lung function metrics from NHANES included Forced Vital Capacity (FVC), Forced Expiratory Volume in 1 s (FEV1), and Peak Expiratory Flow (PEF), while CHARLS provided PEF data. Social isolation was assessed using marital status, living alone, and social participation in both studies, with NHANES including daily life difficulties and CHARLS incorporating infrequent child contact. Weighted linear regression models were used to assess associations. A parallel mediation model was constructed using structural equation modeling, and statistical analysis was performed using the "lavaan" package in R version 4.3.2. Standardized coefficients with p-values and mediation proportions are presented.

A total of 3,575 individuals from NHANES (mean age 63.49 ± 8.27) and 3,752 from CHARLS (mean age 61.00 ± 9.23) were included. Social isolation was significantly associated with lower FVC, FEV1, and PEF in both datasets. In NHANES, mediation analysis revealed significant total indirect effects for: FVC (-0.0628, p < 0.001), 67.0% mediated by smoking, income, activity, and BMI; FEV1 (-0.0666, p < 0.001), 79.3% mediated by the same factors; and PEF (-0.0643, p < 0.001), 49.1% mediated by smoking, income, and activity. Across all three lung function metrics, income contributed the largest proportion of the mediated effect, accounting for 35.32% of FVC, 37.26% of FEV1, and 26.28% of PEF. In CHARLS, only BMI had a significant indirect effect on PEF (-0.0088, p = 0.004), mediating 6.37% of the association.

Social isolation is associated with poorer lung function in both U.S. and Chinese populations aged ≥ 45 years, with distinct mediating pathways. In the U.S., income, smoking, and physical activity play significant roles, while in China, BMI is the primary mediator. Cultural and societal contexts are crucial when addressing the impact of social isolation on respiratory health.