Smoking cessation duration and risk of acute myocardial infarction: A nationwide cohort study in Korea

BACKGROUND AND AIMS: While smoking cessation reduces cardiovascular risk, the precise timeline and temporal dynamics of risk reduction using granular time intervals remain poorly characterized. We aimed to estimate the association between smoking cessation duration and cardiovascular risk using 2-year intervals in a large Asian cohort. DESIGN: Population-based retrospective cohort study. SETTING: South Korea, using the nationwide National Health Insurance Service database (2002-2023). PARTICIPANTS: 1 349 545 adults without prior acute myocardial infarction (AMI) or AMI requiring percutaneous coronary intervention (PCI) who underwent at least four biennial health examinations, comprising 1 059 469 never smokers, 60 927 quitters and 229 149 current smokers. MEASUREMENTS: Smoking status was classified from repeated self-reported examinations; quitters were grouped by cessation duration in 2-year intervals up to ≥8 years. Outcomes were incident AMI and AMI requiring PCI, over a mean follow-up of 10.6 years. Hazard ratios (HRs) were estimated using Cox proportional hazards models adjusted for demographic, clinical and lifestyle covariates including pack-years, with current smokers and never smokers as reference groups. RESULTS: Using current smokers as reference, adjusted HRs decreased progressively with longer cessation duration. Statistically significant risk reduction was evident within 2-3 years [AMI: HR = 0.475, 95% confidence interval (CI) = 0.403-0.559; AMI requiring PCI: HR = 0.437, 95% CI = 0.359-0.532]. Quitters who maintained cessation for ≥8 years achieved risk levels comparable to never smokers (AMI: HR = 0.396, 95% CI = 0.284-0.552 vs. HR = 0.407, 95% CI = 0.386-0.429; AMI requiring PCI: HR = 0.321, 95% CI = 0.209-0.493 vs. HR = 0.366, 95% CI = 0.343-0.389). SUMMARY: In a nationwide Korean cohort, the risk of acute myocardial infarction or acute myocardial infarction requiring percutaneous coronary intervention declined progressively with longer smoking cessation; after 8 or more years of sustained abstinence, risk was no longer distinguishable from that of never-smokers.