Women who have both ovaries removed double their risk of Parkinson's disease, research from the US has found.

It reinforces a growing belief that reduced oestrogen is a risk factor for Parkinson's and other neurological diseases, such as Alzheimer's. Men are at greater risk of Parkinson's than women, and postmenopausal women are at greater risk than other women.

Researchers at Mayo clinic in Rochester, Minnesota, looked for parkinsonism - diseases characterised by tremor, rigidity or stiffness, of which Parkinson's is the most common.

According to Walter Rocca, leading the research: "The risk is higher for women with both ovaries removed; however, it may also be somewhat increased when one ovary is removed ... there is a suggestion that for women with one ovary removed, removal of the uterus may also increase the risk.

"We conducted a previous study suggesting hysterectomy ... and younger age at menopause are related to an increased risk of Parkinson's disease. These findings suggested oestrogen produced normally by the ovaries is involved in protecting the brain during ageing." But he cautioned that for some women, for example those undergoing cancer treatment, risk from retaining the ovaries may far outweigh chances of Parkinson's.