Hormone replacement therapy (HRT) may help post-menopausal women ward off memory loss and Alzheimer's disease.
A study conducted at London's Institute of Psychiatry found that women's memories are affected when their bodies stop producing the hormone oestrogen and were recovered when hormone levels were upped.
Researchers studied 30 pre-menopausal women who were having surgery for benign womb growths.
The participants were given a drug which shuts down the ovaries – creating a state similar to menopause.
They were given memory tests before being given the medication, during the treatment and when its affects had worn off.
Average scores were similar before and after treatment, but dipped by about ten per cent while the women's ovaries were shut down.
"There is growing evidence to support a theory that there is a critical window when you hit the menopause," Dr Michael Craig, the study's leader, said.
"If you have HRT at the time of menopause, it may confer significant protection, but if you don't start it until ten years afterwards, the damage may be done."
According to the Alzheimer's Society, two thirds of people with dementia are women.
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