Researchers have zeroed in on the possible reason for this which could be loss of the female sex hormone estrogen that prevents ageing. Women who are in the risk category for ovarian cancer may also carry a potential risk of dementia.
The researchers monitored 1,209 women who had both ovaries removed, and 1,302 who had one removed, between 1950 and 1987. The analysis was compared with a similar number of women who had not undergone surgery. It was found that women who had been operated stood a 40% chance of suffering cognitive impairment or dementia as compared to those in the healthy control group.
Lead researcher Dr Walter Rocca confirmed that women who have both ovaries removed received estrogen replacement therapy (HRT). But there are chances the treatment would have been discontinued especially in cases where the patient was very young at the time of the surgery.
To quote Dr.Rocca, "Like any medical or surgical decision, there is a trade between risk and benefit. Our findings are important for situations where the removal of the ovaries is elective - that is, conducted to reduce the risk of ovarian cancer."
Henry Scowcroft, of the charity Cancer Research UK, said: "Removing the ovaries is only done when absolutely necessary. It is important to bear this in mind when considering the theoretical risk of possible future problems. These results have not yet been published in a peer-reviewed journal so it is difficult to comment on the relative risks involved."
Dr Susanne Sorensen, head of research at the Alzheimer's Society, said "These results again seem to indicate that there may be a link between the lack of estrogen and the development of dementia, although the researchers state that the link may be more complex than thought earlier."