Risk of dementia according to the smoking habit change after ischemic stroke: a nationwide population-based cohort study.

There is a paucity of research regarding the association between the risk of incident dementia and changes in smoking habits in the acute ischemic stroke population. We aimed to investigate the effects of smoking habit change on the risk of incident dementia in an ischemic stroke population using data from the Korean National Health Insurance Services Database. This nationwide population-based cohort study included 197,853 patients with ischemic stroke. The patients were divided into never smokers, former smokers, smoking quitters, sustained smokers, and new smokers, based on the 2-year change in smoking status between the two consecutive health examinations before and after the index stroke. The patients were followed up from the index date to 2018 to assess the development of dementia. Dementia was further categorized into Alzheimer's, vascular, and other types of dementia according to the International Classification of Diseases, Tenth Revision diagnosis. Multivariable Cox proportional hazards models were used to assess the association between changes in smoking habits and the risk of dementia. After a median of 4.04 years of follow-up, 19,595 (9.9%) dementia cases were observed. Among them, 15,189 (7.7%) were diagnosed with Alzheimer's disease dementia and 2719 (1.4%) were diagnosed with vascular dementia. After adjusting for covariates, including age, sex, alcohol intake habits, cigarette pack-year, regular physical activity, income, history of hypertension, diabetes mellitus, dyslipidemia, and chronic kidney disease, new smokers, sustained smokers, and smoking quitters were significantly associated with a higher risk of all-cause dementia than never smokers (adjusted hazard ratio [aHR] 1.395, 95% confidence interval [CI] 1.254-1.552; aHR 1.324, 95% CI 1.236-1.418; and aHR 1.170, 95% CI 1.074-1.275, respectively). Similar trends were observed for both Alzheimer's dementia and vascular dementia, but the association between new smokers and vascular dementia was not significant. The impact of smoking habit change was more prominent in the 40-65-year-old group. New and sustained smokers had a substantially higher risk of incident dementia after ischemic stroke than never smokers. Smoking quitters also had an elevated risk of incident dementia, but the detrimental effects were lower than those in new and sustained smokers.