Women in a 30-year follow-up study who had ovaries surgically removed before menopause had nearly double the risk for developing age-related dementia later in life. But the increased risk was not seen in women who had both ovaries removed and were also treated with estrogen until at least age 50.
The study, published in the latest online issue of the journal Neurology, suggests there is a "critical age window" for the protective effect of estrogen on women's brains, says researcher Walter A Rocca, MD, MPH, of the Mayo Clinic in Rochester, Minn.
"It is possible that estrogen has a protective effect on the brain and that lack of estrogen due to ovary removal may increase a woman's risk of developing memory problems," Rocca says in a news release.
Estrogen Protects Brain
The study included roughly 1,500 women who had one or both ovaries surgically removed before age 50 and an equal number of women who did not have the surgery.
The women were followed for an average of 27 years, during which time they were interviewed to determine if they had developed memory problems and other age-related cognitive issues.
Rocca and colleagues found that the younger the women were when they had their ovaries removed, the more likely they were to develop dementia later in life unless they received treatment to replace the estrogen their bodies were no longer producing.
Of the 427 women in the study who had surgery to remove both ovaries prior to age 49, only one out of five was also treated with estrogen therapy until at least age 50.
These estrogen-treated women showed no increase in later dementia risk, compared to women who still had their ovaries.
The doubling in risk seen in women who had both ovaries removed but did not have estrogen replacement therapy until at least age 50 has important clinical implications for younger women facing choices about ovary removal and estrogen replacement following surgery, Rocca says.
A Shift in Thinking
Surgical removal of the ovaries, known as oophorectomy, can be performed as a treatment for conditions such as ovarian cysts and endometriosis. But the ovaries may also be removed to reduce a woman's risk of developing some cancers.
For premenopausal women no longer concerned about preserving their fertility, past thinking had been that there was little downside to removing the ovaries when a hysterectomy is performed to remove the uterus.
But that thinking is now changing, Rocca says, because of emerging evidence suggesting that adequate estrogen prior to menopause protects against heart disease, osteoporosis, and now dementia later in life.
"It is now clear that we need to weigh concerns about cancer against concerns about these other diseases in decisions about the preventive removal of the ovaries in women of this age," he tells WebMD.
Estrogen Therapy Revisited
Rocca is quick to point out that his findings do not address the controversial question of whether estrogen therapy is a good idea for women approaching menopause with their ovaries still intact.
But in a separate study, reported last spring, taking estrogen replacement therapy before the age of 65 did appear to protect women from developing dementia later on, whether or not they still had their ovaries.
Participants in the Women's Health Initiative (WHI) Memory Study who took estrogen alone or estrogen plus progestin before age 65 were about 50% less likely to develop Alzheimer's disease or another age-related dementia as women who did not take hormones before that age.
Stanford University professor of neurology Victor Henderson, MD, who led that study, says the clinical implications of all the new research remain somewhat puzzling.
"Despite very important knowledge gained in the WHI Memory Study there are still important unanswered questions concerning the relationship between estrogen and cognition, and the Mayo study offers one more piece of the puzzle," he says.