Relationship Between Estimated Cardiorespiratory Fitness and Chronic Lung Disease in Older Adults: Results from Two National Cohort Studies

Background: The intensification of population aging has significantly elevated the risk of chronic lung disease (CLD) among the elderly. As a comprehensive indicator reflecting the synergistic functions of the cardiovascular and respiratory systems, cardiorespiratory fitness (CRF) requires further exploration regarding its association with CLD in this demographic. Methods: This study included 11,082 adults aged ≥50 years (3,269 from HRS, 4,869 from ELSA) with median follow-ups of 9.78 and 12.11 years. Estimated CRF (eCRF) was calculated via gender-specific algorithms using baseline data (age, BMI, waist circumference, etc.) and categorized into low/medium/high groups. Cox proportional hazards models, subgroup, and sensitivity analyses were performed. Results: The median eCRF was 8.97 METs, with 848 new CLD cases. After adjusting confounders, each 1-SD increase in eCRF reduced CLD risk by 16% (HR=0.84, 95%CI:0.74-0.95) in HRS, and 30% (HR=0.70, 95%CI:0.60-0.82) in ELSA. High vs. low eCRF lowered risk by 30% (HRS, HR=0.70, 95%CI:0.54-0.89) and 55% (ELSA, HR=0.45, 95%CI:0.34-0.62). Restricted cubic splines confirmed a significant dose-response relationship (P<0.05). Subgroup analyses showed consistent protective effects across gender, age, BMI, and smoking status (interaction P>0.05), validated by sensitivity analyses. Conclusions: Higher eCRF is significantly associated with a reduced CLD risk in older adults. Improving cardiorespiratory fitness may be a key strategy for CLD prevention.