Associations of smoking cessation duration with all-cause and selected cause-specific mortality among older adults in Shenzhen, China: a prospective cohort study of 501,932 participants

Smoking poses a major global health threat, and although cessation can reduce mortality risk, the health effects of smoking cessation in older adults with long-term smoking history warrant further investigation. The study included Chinese older adults from the Shenzhen Healthy Ageing Research cohort, a community-based prospective study conducted between 2018 and 2021. We estimated the hazard ratios with 95% confidence intervals for all-cause or cause-specific mortality using Cox proportional hazards models and restricted cubic spline (RCS). Compared with current smokers, participants who had quit more recently had higher subsequent mortality, with the highest risk observed among those who had quit 2–4 years before baseline. Compared to current smokers, the hazard ratio for all-cause mortality was 0.87 (0.81–0.94) for never smokers, 1.70 (1.40–2.07) for transient quitters (< 2 consecutive years since smoking cessation), 1.13 (0.97–1.31) for recent quitters (2–6 consecutive years since smoking cessation), and 0.89 (0.80–0.99) for long-term quitters (> 6 consecutive years since smoking cessation). Subgroup analyses indicated that among recent quitters, those who were younger, had a shorter smoking history, and maintained a healthier lifestyle, including regular exercise, had lower mortality than those who were older, had a longer smoking history, or did not exercise. Among older adults with long-term smoking histories, recent smoking cessation was associated with higher subsequent all-cause and cancer mortality compared with continued smoking. While reverse causation remains the most plausible explanation, this association highlights a potentially vulnerable period in which older quitters may benefit from enhanced clinical surveillance and support.