Removal of a woman's ovaries leads to an increased risk of mental decline in older age, a study has found.
The procedure, which triggers a "surgical menopause", is most often carried out on younger women because of cancer.
It usually accompanies removal of the womb, or hysterectomy.
Scientists studied 1,837 women aged between 53 and 100, a third of whom had experienced a surgical menopause.
The women were given tests to measure thinking skills and memory. They showed that having a surgical menopause at an earlier age was associated with faster declines in thinking ability and certain kinds of memory.
Long-term memory relating to concepts and ideas and episodic memory of events were both affected.
The findings were presented today at the American Academy of Neurology's annual meeting in San Diego, US.
Lead scientist Dr Riley Bove, from Harvard Medical School in Boston, said the results suggested a potential benefit from hormone replacement therapy.
"While we found a link between surgical menopause and thinking and memory decline, women on longer hormone replacement therapies had slower declines," said study author Riley Bove, MD, with Harvard Medical School in Boston and a member of the American Academy of Neurology.
"Since hormone replacement therapy is widely available, our research raises questions as to whether these therapies have a protective effect against cognitive decline and whether women who experience early surgical menopause should be taking hormone replacement therapies afterward."
A significant association was also seen between age at surgical menopause and the brain deposits linked to Alzheimer's disease.
"Our study warrants further research as the interest in this subject will continue to grow right along with our ageing population," said Dr Bove.