Mendelian randomization analysis of UK and Danish cohorts establishes that each standard deviation increase in BMI raises vascular dementia risk by 63%, with blood pressure changes mediating only 18-25% of this effect. The genetic analysis, which removes confounding variables that plague observational studies, demonstrates a direct causal pathway from excess weight to cognitive decline through vascular mechanisms. This finding distinguishes vascular dementia from Alzheimer's disease, where obesity's role remains less clear. The research strengthens the case for midlife weight management as dementia prevention, particularly given that vascular dementia accounts for roughly 20% of all dementia cases. However, the study's limitation lies in examining only four metabolic mediators—blood pressure, cholesterol, glucose, and inflammation—leaving other potential pathways unexplored. The relatively modest mediation by blood pressure suggests obesity triggers vascular brain damage through multiple mechanisms beyond hypertension alone. For health-conscious adults, this provides compelling evidence that maintaining healthy weight isn't just about cardiovascular health or diabetes prevention, but represents a crucial strategy for preserving cognitive function decades later.