Associations of Hysterectomy and Oophorectomy with Dementia Risk: A Systematic Review and Meta-Analysis of Observational Studies.

Objectives: The aim was to evaluate associations of hysterectomy and oophorectomy with dementia-related outcomes while distinguishing specific surgical procedures. Methods: PubMed, Embase, and the Cochrane Library were searched from inception and updated through 20 August 2026. Adjusted hazard ratios (HRs), risk ratios (RRs), and odds ratios (ORs) were synthesized on the log scale using generic inverse-variance random-effects models with restricted maximum likelihood. Quantitative pools were restricted to explicitly defined procedures; mild cognitive impairment (MCI) was kept separate from dementia and Alzheimer's disease (AD). Results: Nine reports involving 2,693,443 participants were included in the systematic review, of which five contributed to at least one procedure-specific meta-analysis. Hysterectomy without documented adnexal surgery was not clearly associated with dementia/AD (4 studies; pooled ratio 0.94, 95% confidence interval [CI] 0.84-1.05; I2 = 82.2%). Hysterectomy with bilateral salpingo-oophorectomy/oophorectomy also showed no clear association (2 studies; 1.04, 95% CI 0.67-1.62; I2 = 83.6%), nor did bilateral oophorectomy alone (4 studies; 0.99, 95% CI 0.88-1.12; I2 = 75.6%). No independently extractable study evaluated hysterectomy with bilateral salpingectomy. Conclusions: Procedure-specific analyses did not demonstrate a clear association with dementia or AD, but substantial heterogeneity, residual confounding, and exposure misclassification limit certainty and preclude causal interpretation.