Objective: There is increasing laboratory evidence for a neuroprotective effect of estrogen; however, the clinical and epidemiologic evidence remains limited and conflicting. We studied the association of oophorectomy performed before the onset of menopause with the risk of subsequent cognitive impairment or dementia. Methods: We included all women who underwent unilateral or bilateral oophorectomy before the onset of menopause for a non-cancer indication while residing in Olmsted County, MN, from 1950 through 1987. Each member of the oophorectomy cohort was matched by age to a referent woman from the same population who had not undergone oophorectomy. In total, we studied 813 women with unilateral oophorectomy, 676 women with bilateral oophorectomy, and 1,472 referent women. Women were followed through death or end of study using either direct or proxy interviews. Results: Women who underwent either unilateral or bilateral oophorectomy before the onset of menopause had an increased risk of cognitive impairment or dementia compared to referent women (hazard ratio [HR] = 1.46; 95% CI 1.13 to 1.90; adjusted for education, type of interview, and history of depression). The risk increased with younger age at oophorectomy (test for linear trend; adjusted p < 0.0001). These associations were similar regardless of the indication for the oophorectomy, and for women who underwent unilateral or bilateral oophorectomy considered separately. Conclusions: Both unilateral and bilateral oophorectomy preceding the onset of menopause are associated with an increased risk of cognitive impairment or dementia. The effect is age-dependent and suggests a critical age window for neuroprotection.

The Rochester Epidemiology Project (REP) is a unique research infrastructure in which the medical records of virtually all persons residing in Olmsted County, Minnesota, for over 40 years have been linked and archived. In the present article, the authors describe how the REP links medical records from multiple health care institutions to specific individuals and how residency is confirmed over time. Additionally, the authors provide evidence for the validity of the REP Census enumeration. Between 1966 and 2008, 1,145,856 medical records were linked to 486,564 individuals in the REP. The REP Census was found to be valid when compared with a list of residents obtained from random digit dialing, a list of residents of nursing homes and senior citizen complexes, a commercial list of residents, and a manual review of records. In addition, the REP Census counts were comparable to those of 4 decennial US censuses (e.g., it included 104.1% of 1970 and 102.7% of 2000 census counts). The duration for which each person was captured in the system varied greatly by age and calendar year; however, the duration was typically substantial. Comprehensive medical records linkage systems like the REP can be used to maintain a continuously updated census and to provide an optimal sampling framework for epidemiologic studies.

The Rochester Epidemiology Project (REP) medical records-linkage system was established in 1966 to capture health care information for the entire population of Olmsted County, MN, USA. The REP includes a dynamic cohort of 502 820 unique individuals who resided in Olmsted County at some point between 1966 and 2010, and received health care for any reason at a health care provider within the system. The data available electronically (electronic REP indexes) include demographic characteristics, medical diagnostic codes, surgical procedure codes and death information (including causes of death). In addition, for each resident, the system keeps a complete list of all paper records, electronic records and scanned documents that are available in full text for in-depth review and abstraction. The REP serves as the research infrastructure for studies of virtually all diseases that come to medical attention, and has supported over 2000 peer-reviewed publications since 1966. The system covers residents of all ages and both sexes, regardless of socio-economic status, ethnicity or insurance status. For further information regarding the use of the REP for a specific study, please visit our website at www.rochesterproject.org or contact us at info@rochesterproject.org. Our website also provides access to an introductory video in English and Spanish.