Association between Circadian Syndrome and Incident Chronic Lung Disease: A Dual-Cohort Prospective Study

Background Circadian syndrome (CircS) is a novel clinical issue integrating systemic circadian disruption with cardiometabolic risk factors. Although isolated rhythm disturbances are associated with respiratory pathology, the longitudinal effect of CircS on the incidence of chronic lung disease (CLD) remains undescribed. We investigated this association and validated its universality across distinct genetic and environmental contexts. Methods We conducted a prospective dual-cohort study using data from the China Health and Retirement Longitudinal Study (CHARLS, n = 7,553) as the discovery cohort and data from the English Longitudinal Study of Ageing (ELSA, n = 4,957) as the validation cohort. CircS was defined by the clustering of at least four of the seven circadian-metabolic components, including central obesity, high blood pressure, glucose, and triglycerides, low HDL-C levels, short duration of sleep, and depression. Multivariate Cox proportional hazards models were constructed to estimate hazard ratios (HRs) for incident CLD over a follow-up of seven years, adjusting for sociodemographic and lifestyle confounders. Results We found that in the discovery cohort (CHARLS), CircS was independently associated with an increased risk of incident CLD (fully adjusted HR  = 1.16, 95% CI  = 1.01–1.33). This association was confirmed in the validation cohort (ELSA), with a stronger effect size ( HR  = 1.53, 95% CI  = 1.20–1.95). Phenotypic comparison revealed that while the association was consistent across subgroups in the Chinese population, it was significantly modulated by alcohol consumption in the British population ( P  < 0.05). The risk was disproportionately higher among drinkers, supporting a synergistic “double hit” mechanism between circadian misalignment and lifestyle stressors. Conclusion Circadian syndrome serves as a robust and independent predictor of respiratory decline across various populations. These findings challenge traditional organ-centric prevention models and emphasize that circadian integrity is a reliable indicator of respiratory vulnerability. Public health strategies that integrate holistic chronomedicine approaches, focusing on sleep hygiene and moderate alcohol consumption, may reveal novel pathways to mitigate the global burden of CLD.