New research suggests that premenopausal women who have their ovaries removed have an increased risk of developing neurological disorders such as dementia and Parkinsonism.
Two newly published say there is a critical age window for neuroprotection by estrogen and they raise questions about the protective benefits of estrogen on the brain and the long-term risks of removing the ovaries before menopause.
The surgical removal of the ovaries, known as oophorectomy, is 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.
Researchers at the Mayo Clinic in Rochester, Minnesota interviewed 1,489 women who had undergone ovarian surgery; 813 women had one ovary removed, and another 676 had both ovaries removed; they were matched to 1,471 other women by age who were used as the control group.
The women from Olmsted County, Minnesota, underwent the surgery between 1950 and 1987, for a benign ovarian condition before the onset of menopause and were tracked for an average of 27 years.
The study participants were interviewed by telephone in order to determine the rates of memory impairment, limitations in activities of daily living, and diagnosis of dementia, senility or Alzheimer's disease.
The investigators also factored in the possible affects of age, educational level and history of depression.
According to lead investigator Dr. Walter A. Rocca and his associates, of the subjects who had one or both ovaries removed, 150 had cognitive impairments or dementia, compared with 98 of the controls, which they say is a statistically significant difference.
Rocca and his colleagues also saw a significant trend for increased risk of neurological deficits with women of a younger age who had such surgery, unless the women received estrogen replacement therapy until at least 50 years of age.
For the second study using the same group of women, Rocca and colleagues also identified a significantly increased risk of Parkinsonism for women who had one or both ovaries removed if the surgery was conducted before 41 years of age.
The researchers found these women were 75 percent more likely to have Parkinsonism.
Parkinsonism includes any condition that causes the symptoms of Parkinson's disease which is one of the most common age-related neurological disorders.
Symptoms include tremor, stiffness of the arms, legs or trunk of the body, loss of facial expression, loss of control over movement, paralysis and impaired mental processes (cognitive dysfunction).
The researchers say as with cognitive impairment and dementia, the effect of surgery was age-dependent and the risk increased when the surgery was carried out at a younger age.
Rocca and his associates conclude that the neuroprotective effect of estrogen may be general and may involve multiple mechanisms and multiple types of brain cells.
The researchers say the studies are among the first to support the hypothesis of a critical age window for the protective effect of estrogen on the brain in humans.
In the past premenopausal women who were no longer concerned about preserving their fertility, had their ovaries removed when a hysterectomy was performed to remove the uterus.
Rocca says emerging evidence however suggests that adequate estrogen prior to menopause protects against heart disease, osteoporosis, and now also dementia later in life.
The studies are published in the current edition of Neurology.