The study on dementia involved approximately 1,500 women who underwent the removal of one or both ovaries for non-cancer-related reasons, such as ovarian cysts, endometriosis, or for the prevention of ovarian cancer. 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. If the women could not be interviewed directly, the investigators interviewed a family member.
Researchers found that women who had one or both ovaries removed before menopause were nearly two times more likely to develop cognitive problems or dementia compared to women who did not have the surgery. In addition, those women 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 Walter A. Rocca, MD, MPH, with the Mayo Clinic in Rochester, MN, and member of the American Academy of Neurology.
Rocca says this is one of the first studies to show there may be a critical age window for the protective effect of estrogen on the brain in women. Before this study, knowledge was based almost exclusively on animal experiments. 'For example, the study found 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 of developing memory problems. These findings suggest that estrogen is protective for these women in this age window. By contrast, past studies from the Women's Health Initiative have shown that estrogen use started at age 65 years or later may have a negative effect on memory and may increase the risk of developing dementia,' 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 percent of women received some estrogen treatment after both of their ovaries were removed, only 20 percent of them received estrogen treatment until at least age 50. Age 50 is the median age when women reach natural menopause.'
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 two times more likely to develop Parkinsonism, a syndrome involving tremor at rest, muscle rigidity, and slowness of movements. The most common form of this syndrome is Parkinson's disease. The risk for Parkinsonism 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.