BACKGROUND: The apolipoprotein E (APOE) gene represents the strongest genetic determinant of sporadic Alzheimer's disease (AD), yet its interaction with sex-specific endocrine factors remains poorly understood. Lifetime estrogen exposure, estimated through reproductive lifespan, may modulate neurodegenerative risk, but findings are inconsistent. Previous studies have examined reproductive factors and APOE interactions in relation to cognitive outcomes, but dose-dependent effects across all APOE ...