WEDNESDAY, Aug. 29, 2007 (HealthDay News) -- Removing one or both ovaries before a woman reaches natural menopause increases the risk of both dementia and movement disorders such as Parkinson's disease.
But giving hormone-replacement therapy at least until the age of 50 blunts that risk, according to a study by Mayo Clinic researchers.
"It's the first study that shows that taking out the major source of endogenous estrogen, which is ovaries, will have this impact on movement disorders and one of the first with dementia," said Farida Sohrabji, an associate professor of neuroscience and experimental therapeutics at Texas A&M Health Science Center College of Medicine.
The study findings were published in the Aug. 29 online issue of Neurology.
A woman's ovaries are her main source of endogenous (produced by the body) estrogen.
There has been some evidence that estrogen can protect against cognitive decline, although the landmark Women's Health Initiative (WHI) study actually showed the opposite for women aged 65 and older.
The authors of the new study used the Rochester Epidemiology Project, a database of records dating from 1935 housed at the Mayo Clinic in Rochester, Minn, to identify all women in Olmsted County, Minn., who had had one or both ovaries removed between 1950 and 1987. These women were then compared to a control group. Each group consisted of about 1,500 women.
The researchers then interviewed women in both groups (or their relatives) to assess any degree of cognitive impairment or dementia, and compared the two groups. Women who were still alive also underwent a cognitive test over the phone.
Those women who had had one or both ovaries removed before menopause were almost twice as likely to develop cognitive problems or dementia, compared with women who did not have this surgery, known as oophorectomy.
Women who were younger when they underwent oophorectomy were more likely to develop dementia than women who were older at the time of the surgery. The removal of ovaries is often done to protect women at high risk of breast or ovarian cancer.
According to the study authors, women and doctors should think twice before going ahead with such a surgery.
There has also been some evidence that estrogen helps protect against movement disorders, although some studies have shown that the hormone might be detrimental.
To assess this risk, the same set of Mayo Clinic researchers looked at many of the same women involved in the dementia study. This group included more than 2,000 women who had had one or both ovaries removed, and a similar control group of women.
Women who had undergone a unilateral or bilateral oophorectomy (one or both ovaries, respectively) before the onset of menopause were again almost twice as likely to develop Parkinsonism, a syndrome involving movement and muscle problems, the most common form of which is Parkinson's disease.
Again, the younger the woman was when she had her ovary or ovaries removed, the greater the chance she would develop a movement disorder.
The findings do need to be replicated, the study authors cautioned.
With hormones, timing may be everything.
"What seemed to matter was the length of time that women were exposed to hormone therapy," Sohrabji said. "The shorter that duration, the more likely they were to show dementia and movement disorders, and that's consistent with the idea that there's a critical period for hormone therapy. It also goes very well with data that recently emerged from the WHI regarding cardiovascular risk being much less in women who took estrogen earlier."
"All of these studies seem to be definitely pointing that there is a critical window for hormone therapy," she continued. "It speaks both to a critical [time] window and a critical duration."
Learn more about ovary removal from the Mayo Clinic.