Abstract
BACKGROUND: Although the association between cigarette smoking and respiratory disorders is well established, the long-term impact of early initiation of smoking on overall health and respiratory diseases remains insufficiently characterized. METHODS: Using data from 157,699 participants in the UK Biobank (UKB) and 21,727 participants in the National Health and Nutrition Examination Survey (NHANES), we systematically evaluated the associations between early smoking initiation and a broad range of health outcomes. RESULTS: Participants who initiated smoking at an early age exhibited multiple adverse health outcomes. Early smoking was associated with a substantially increased risk of chronic lower respiratory diseases, accelerated decline in lung function, and elevated mortality. Further analyses highlighted the potential contribution of chemical pollutants in cigarette smoke to these detrimental effects. Notably, early smoking predominantly affected airway epithelial integrity and inflammatory pathways, and this association was partly mediated by cadmium exposure, a toxic metal commonly present in cigarette smoke. CONCLUSIONS: The observed associations between early smoking initiation and a spectrum of unfavorable health outcomes underscore the urgent need for increased attention from healthcare professionals and society as a whole. Strengthened efforts to prevent adolescent smoking may play a critical role in reducing the future burden of chronic obstructive pulmonary disease (COPD) and other smoking-related diseases. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12890-026-04229-8.