Weight instability and risk of incident dementia among older stroke survivors: A nationwide cohort study.

BackgroundWeight loss, weight gain, and body mass index (BMI) instability have been linked to dementia risk in older adults. Stroke survivors may be particularly vulnerable to accelerated cognitive decline due to impaired physiological reserve and nutrition-related challenges. However, evidence on BMI change and dementia in this high-risk population remains limited.ObjectiveTo investigate the association between annual BMI change and incident dementia in a nationwide cohort of older stroke survivors.MethodsUsing KNHIS data, we identified adults aged ≥65 years with a history of stroke who underwent repeated health examinations. Annual BMI change was categorized as decreased (≤-1 kg/m2/year), stable (-1 to <1), or increased (≥1). Incident dementia (2013-2022) was defined using ICD-10 diagnostic codes combined with anti-dementia medication prescriptions. Multivariable Cox proportional hazards models and stratified analyses were conducted.ResultsAmong 26,174 older stroke survivors, 6727 developed dementia over a mean follow-up of 5.40 ± 2.73 years. Compared with stable BMI, both BMI decrease (HR 1.19; 95% CI 1.13-1.26) and BMI increase (HR 1.13; 95% CI 1.06-1.20) were associated with elevated dementia risk. The association for BMI decrease was consistent across sex and baseline BMI strata, whereas the association for BMI increase was primarily observed in men and those with normal baseline BMI.ConclusionsBoth BMI decreases and increases were associated with elevated dementia risk, with BMI decline showing the most consistent associations across subgroups. These findings suggest that monitoring weight trajectories may help identify older stroke survivors at heightened dementia risk in routine clinical practice.