Abstract
INTRODUCTION: Smoking is a known risk factor for dementia, but the effects of changes in smoking behavior after a depression diagnosis remain unclear. METHODS: We conducted a nationwide cohort study of 1,290,530 individuals newly diagnosed with depression in South Korea between 2009 and 2012. Participants were categorized by smoking status before and after diagnosis. Incident dementia, including Alzheimer disease (AD) and vascular dementia (VD), was tracked through 2018. Adjusted hazard ratios (HRs) were estimated using Cox models. RESULTS: Continued smoking showed the highest dementia risk (HR 1.338 for all-cause; 1.323 for AD; and 1.524 for VD). Quitting reduced risk but remained higher than in persistent non-smokers. Middle age was a key risk period for AD. For VD, men had consistently higher risk, while women had increased risk only in the cessation group. CONCLUSIONS: Changes in smoking behavior after depression diagnosis influence dementia risk, underscoring the need for cessation strategies.