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The findings come from two separate studies carried out by the Mayo Clinic in Minnesota. Both involved women who had oophorectomies because of ovarian cysts, endometriosis or a high risk of ovarian cancer and were followed up for 27 years.

One study involved 813 women who had one ovary removed and 676 who had both removed.

They were followed up along with almost 1,500 women who had not undergone oophorectomy.

This showed that women who underwent unilateral or bilateral oophorectomy were 50 per cent more likely to develop cognitive impairment or dementia, compared with controls.

The risk was highest for women who had oophorectomy when younger. But indication for ovary removal had no impact.

Similar findings were noted for parkinsonism in the second study. This involved a cohort of 1,252 women with unilateral oophorectomy and 2,368 controls.

During follow-up, women who underwent any form of oophorectomy were 68 per cent more likely to develop parkinsonism than controls. Women who underwent the surgery at a younger age were most likely to develop a movement disorder.

Low oestrogen levels following oophorectomy may be to blame, suggested the researchers.

Given the apparent age-dependent nature of the associations, it may be that there is a 'critical window for neuroprotection', they added.

Oestrogen therapy until the age of 50 could help reduce this risk, suggests the team.