Importance: The association between smoking cessation and cardiovascular disease (CVD) risk in relation to cumulative smoking exposure remains poorly understood.
Objective: To evaluate the associations among smoking cessation, lifetime smoking burden, and CVD risk according to the number of years elapsed after smoking cessation.
Design, setting, and participants: This retrospective cohort study of the Korean National Health Insurance Service database investigated smoking duration and intensity between January 2006 and December 2008. Participants were categorized by self-reported smoking habits as current, ex-, or never-smokers. Smoking records were updated every 2 years until December 2019, with participants whose smoking status changed or whose smoking status was unclear excluded. Data analysis was performed between June and December 2022.
Exposures: Time-updated self-reported smoking status, years since quitting, and cumulative smoking amount (pack-years [PY]).
Main outcomes and measures: The primary outcome was incidence and hazard ratio of CVD (composite of cardiovascular death, myocardial infarction, stroke, and heart failure).
Results: Overall, 5 391 231 participants (39.9% male; mean [SD] age, 45.8 [14.7] years; 853 756 [15.8%] current smokers, 104 604 [1.9%] ex-smokers, and 4 432 871 [82.2%] never smokers) were followed up for a mean (SD) of 4.2 (4.4) years. The median (IQR) baseline cumulative smoking amounts were 14.0 (7.5-20.0) PY in current smokers and 10.5 (5.3-20.0) PY in ex-smokers. The median (IQR) duration of smoking cessation was 4 (2-8) years for ex-smokers. Regardless of continued smoking, a dose-dependent association was evident between smoking and incident CVD. Compared with current smokers, ex-smokers with a lifetime smoking burden of less than 8 PY (light ex-smokers) experienced a significant reduction in CVD risk within 10 years of cessation, with a CVD risk similar to that of never-smokers. Conversely, ex-smokers with at least 8 PY (heavy ex-smokers) exhibited a slower decline in CVD risk than light ex-smokers, requiring more than 25 years for the residual CVD risk to disappear.
Conclusions and relevance: In this cohort study, smoking and CVD risk exhibited a dose-dependent association, with light ex-smokers having a CVD risk similar to that of never-smokers relatively soon after smoking cessation. For heavy ex-smokers, greater than 25 years might be required for the residual CVD risk to align with that of never-smokers.