Women who have their ovaries removed before they reach menopause are at an increased risk of later developing dementia and Parkinson's disease.
However, women who had both their ovaries removed but were treated with estrogen until at least age 50 did not have any increased risk, find two studies published in Neurology.
The studies are among the first to provide significant evidence about the benefits of ovarian preservation in young women and the brain-protecting role of estrogen.
The study on dementia involved almost 1,500 women who had either one or both ovaries removed for non-cancer-related reasons, such as ovarian cysts or endometriosis.
The women were compared to an equal number of women who still had both ovaries at the beginning of the study. All participants were followed for a median of 27 years and were interviewed about their memory.
Researchers found that women who had one or both ovaries removed before menopause were nearly twice as likely to develop cognitive problems or dementia compared to women who did not have the surgery. In addition, those who were younger when their ovaries were removed were more likely to develop dementia than women who were older when their ovaries were removed.
"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," said study author Dr. Walter A. Rocca, with the Mayo Clinic in Rochester, Minn.
Many of the women involved in the dementia study were also included in a larger study that found women who had one or more ovaries removed before menopause were nearly twice as likely to develop Parkinsonism, a syndrome that includes Parkinson's disease. The risk for Parkinsonism also increased with younger age at ovary removal.
"Similar to the findings for dementia, these findings may be explained by a premature loss of estrogen and decreased neuroprotection," said Rocca.
Rocca says these findings have important clinical implications and should prompt physicians to reassess removing ovaries before menopause and the use of estrogen treatment following such surgery.
"Although almost 60 per cent of women received some estrogen treatment after both of their ovaries were removed, only 20 per cent of them received estrogen treatment until at least age 50. Age 50 is the median age when women reach natural menopause."
