Smoking cessation duration and risk of ischemic stroke: A nationwide cohort study in Korea.

OBJECTIVES: Smoking cessation is a cornerstone of stroke prevention, but the temporal pattern of risk attenuation remains insufficiently characterized. We evaluated the association between the duration of sustained smoking cessation and incident ischemic stroke using granular 2-year categories to determine the abstinence duration required for quitters to approach the risk level of never smokers. STUDY DESIGN: This population-based retrospective cohort study used the Korean National Health Insurance Service database from 2002 to 2023. We included adults with at least four health examinations between 2002 and the index date (2009-2013), and excluded those with prior cerebrovascular disease or major cardioembolic conditions. Smoking status was classified as never smokers, sustained quitters, and current smokers. MAIN OUTCOME MEASURES: The primary outcome was incident ischemic stroke identified from claims records after the index date. Cox proportional hazards models were used to estimate hazard ratios and 95% confidence intervals adjusted for demographic and cardiometabolic factors, and cumulative smoking exposure. RESULTS: The cohort comprised 1,326,718 participants (1,038,850 never smokers, 60,198 sustained quitters; 227,670 current smokers) with 24,791 incident strokes over 14,072,175 person-years. Compared with current smokers, ischemic stroke risk generally decreased with increasing cessation duration, with the lowest hazards observed in the 6-7-year cessation group. When never smokers were used as the reference group, estimates among quitters with 2-3 years of sustained abstinence were close to those observed among never smokers. CONCLUSIONS: Sustained smoking cessation was associated with progressively lower ischemic stroke risk overall, with substantial risk attenuation observed after prolonged abstinence.