The creatinine-to-cystatin C ratio (a surrogate marker of muscle mass) as a predictor of lung function decline in older adults: A nationwide longitudinal study in China

•Higher CCR was associated with lower risk of severe airflow limitation in older community-dwelling adults.•The annual decline in PEF and PEF% pred was more likely to be slow in participants with higher baseline CCR levels.•CCR may be a potential marker to monitor and predict lung function decline in middle-aged and older adults.