Estrogen has long been thought to be protective against the effects of dementia. Yet so many more women have dementia than men. Today at the International Conference on Alzheimer’s Disease Dr Walter Rocca of Mayo Clinic Minnesota, reviewed the results of the Mayo Clinic Cohort Study of Oophorectomy and Aging.
I found it startling to hear him say that estrogen may be protective against dementia until older age when it may become toxic to the older woman and make her more vulnerable to the effects of dementia.
His study followed a large cohort of women who had had their ovaries removed prior to menopause (before 50 years) and a group of women who had not had this surgery and who had normal reproductive function into menopause, and followed them up an average of 27 years later. What he found was that those who has their ovaries removed prior to the onset of menopause and who had not had estrogen replacement therapy had a significant increase in their risk of dementia compared to the reference group. It was just as true for removal one ovary as for two.
He was reluctant to say that the removal of the ovaries and subsequent drop in estrogen levels caused the dementia as the link between these two events is not clear.
His group also found that older age women who had not had their ovaries removed and those who had estrogen therapy 10-15 years after the removal of their ovaries had an increased risk of dementia.
One hypothesis is that the removal of the ovaries also caused a drop in progesterone and testosterone levels, Genetic factors and some lifestyle factors such as smoking and obesity could also be important. However, he was reluctant to come to a firm conclusion just yet. One of his hypotheses is that estrogen is protective in the early years and becomes neurotoxic in later years although he was unable to explain why this would be so.
This study has significant implications for the post-operative treatment choices that are offered to women so that they are given the information about neuroprotectivity and offered the choice of estrogen therapy in a timely way.
The implications for later life are unclear at this stage.