Oophorectomy, hysterectomy, and risk of Alzheimer's disease: a nationwide case-control study.

Background: Association between oophorectomy and/or hysterectomy and dementia in context of hormone therapy (HT) use is ambiguous.

Objective: To assess whether oophorectomy, hysterectomy, and hysterectomy with bilateral oophorectomy are related to risk of Alzheimer's disease (AD), whether the possible indication for surgery plays a role, and if the associations are modified by HT.

Methods: Our nationwide register based case-control (1 : 1) study included all women with clinically-verified AD diagnoses, residing in Finland on December 31, 2005 (n of cases = 19,043, n of controls = 19,043). AD cases, diagnosed according to NINCS-ADRDA and the DSM-IV criteria, were identified from Special Reimbursement Register. Information on HT use was collected from national prescription register, and data on surgery and uterine/ovarian/cervical cancer were obtained from the hospital discharge register. Most of the women (91.8%) were over 51 years of age when the surgery was performed.

Results: Oophorectomy, hysterectomy, and hysterectomy with bilateral oophorectomy were associated with lower risk of AD (OR/95% CI: 0.85/0.75-0.97, 0.89/0.81-0.97 and 0.85/0.75-0.98, respectively) among women without the history of uterine/ovarian/cervical cancer, although the absolute risk difference was small. The association was not evident in women with uterine/ovarian/cervical cancer history (3.00/0.20-44.87 for all surgeries). The associations were not modified by HT use, which was independently associated with AD risk, with longer use showing protective association.

Conclusion: Our findings indicate that oophorectomy with or without hysterectomy after commencement of natural menopause is not an important determinant of AD risk in older age and support the critical window hypothesis for HT use.