Ovary removal and the risk of dementia

Removal of one or both ovaries before the menopause can almost double a woman’s risk of dementia in old age, reported The Guardian . In addition, “the younger the woman was when she had the operation, the higher her risk of dementia”, the newspaper stated.

The story is based on a study involving about 1,500 women who had one or both ovaries removed between 1950 and 1987. A doubling of the risk of dementia was only apparent for a younger group of women. The total number of women who developed dementia, or cognitive impairment, is small (248) compared to the total number recruited to the study (3000).

Where did the story come from?

Walter Rocca and colleagues from the Department of Health Sciences Research at the Mayo Clinic College of Medicine in Rochester, US, conducted this research. The study was funded by the National Institute of Neurological Disorders and Stroke and the National Institute of Arthritis and Musculoskeletal and Skin Diseases and was published in the peer-reviewed medical journal: Neurology .

What kind of scientific study was this?

The study was a retrospective cohort study of women who had one or both of their ovaries removed for a variety of reasons, including cysts, inflammation, and endometriosis before the menopause. This group was then compared with women of the same age who had not had ovary removal. All of these women were originally enrolled in a larger study – the Mayo Clinic cohort Study of Oophorectomy and Aging.

Women who had ovaries removed as a treatment for ovarian or other cancers were not included in the study. At some point after their surgery (believed to be around 2002), the researchers attempted to contact the women to determine their cognitive and dementia status. They interviewed women by telephone, if the women were not available for interview (due to disability or death), someone in the family answered questions on their behalf. Participants who could not be contacted by telephone were not included in this study.

What were the results of the study?

The researchers found that the women who had undergone removal of either one or both of their ovaries before menopause had a 46% greater risk of cognitive impairment or dementia after the age of 40 compared with women who had not had the surgery. The researchers also found that a younger age at the time of surgery appeared to increase this risk.

What interpretations did the researchers draw from these results?

The researchers concluded that removal of the ovaries before menopause is associated with an increased risk of cognitive impairment or dementia and that this risk is age-dependent.

What does the NHS Knowledge Service make of this study?

Though this is a well conducted, relatively large study, some factors need to be considered when interpreting the results:

• Cognitive impairment and dementia were relatively rare in these populations and the overall increased risk of 46% represents an absolute change from 7 women in 100 to 10 women in 100. 
• Only 62% of the total number of women available participated in the interviews for this study. 
• Though the authors tried to capture some of the characteristics that could be responsible for both increased risk of ovarian removal and increased risk of dementia (e.g. age, indication for ovary removal), there may be other factors that predispose a woman to both that they were unable to control for.
• As the authors acknowledge, assessment of dementia using telephone interviews is ‘imperfect’. 
• The eight-part questionnaire that the researchers used to assess dementia had only previously been tested by them in a single separate study.
• The study examined the effects of surgery that was carried out, in some cases, over 50 years ago. Medical practice has changed over the 27 years since the most recent surgery included in this study; an up-to-date study could provide more relevant findings for medical practice.