Women who have had ovarian surgery before menopause are much more likely to develop dementia or parkinsonism years later without estrogen therapy, according to a pair of observational analyses.

“It’s possible that estrogen has a protective effect on the brain and that a lack of estrogen due to ovary removal may increase a woman’s risk” of developing memory problems or parkinsonism, says lead study author Walter A. Rocca, MD, MPH. The dementia study enrolled 1,489 women who had undergone single or double oophorectomy between 1950 and 1987.

Dr. Rocca’s team at the Mayo Clinic in Rochester, Minn., compared these patients with women of similar age and background whose ovaries were intact. They found that after 27 years, women who had had surgery had a 46% higher risk of cognitive impairment or dementia than those who hadn’t and a 68% higher risk of parkinsonism.

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The younger a woman was at the time of her oophorectomy, the higher her risk for developing either condition. The pattern held up whether a woman lost one ovary or both and no matter why she had her surgery (Neurology. 2007;69:1074-1083).

Women who had both ovaries removed before age 49 but were given estrogen treatment until at least age 50 did not have an increased risk. These findings suggest that estrogen is protective for these women in this age window. Fifty is the median age for the natural onset of menopause.