HORMONE replacement therapy (HRT) may help prevent Alzheimer’s disease in women at risk of developing the condition, researchers have suggested.

A team said the use of HRT, which helps control symptoms of the menopause, is associated with better memory, cognitive function and larger brain volumes in later life in women carrying a gene called APOE4.

About a quarter of women in the UK are thought to carry the APOE4 gene and Alzheimer’s is more common in women than men.

APOE4 is the strongest risk factor gene for Alzheimer’s disease, although inheriting APOE4 does not mean someone will definitely develop the condition.

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In a new study, researchers found that HRT was most effective when given during perimenopause - where symptoms build up months or years before periods actually stop - and could lead to brains that appear several years younger.

The research was co-led by Craig Ritchie, a professor of the psychiatry of ageing at Edinburgh University.

Prof Ritchie said the study “highlights the need to challenge many assumptions about early Alzheimer’s disease and its treatment, especially when considering women’s brain health”.

He said: “An effect on both cognition and brain changes on MRI supports the notion that HRT has tangible benefit. These initial findings need replication, however, in other populations.”

Alzheimer’s disease is most common in people over the age of 65.

The risk of Alzheimer’s and other types of dementia increases with age, affecting an estimated one in 14 people over the age of 65 and one in every six over the age of 80.

Co-author Professor Anne-Marie Minihane, from the University of East Anglia’s Norwich Medical School, said: “We know that 25 per cent of women in the UK are carriers of the APOE4 gene and that almost two thirds of Alzheimer’s patients are women.

“In addition to living longer, the reason behind the higher female prevalence is thought to be related to the effects of menopause and the impact of the APOE4 genetic risk factor being greater in women.

“We wanted to find out whether HRT could prevent cognitive decline in at-risk APOE4 carriers.”

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The experts studied data from 1,178 women taking part in the European Prevention of Alzheimer’s Dementia initiative, which was set up to study participants’ brain health over time.

The project, which involved 10 countries, tracked the brains of 1,906 people over 50, who did not have dementia at the start of the study.

For the latest research, experts looked at the results of cognitive tests and brain volumes as recorded by MRI scans.

The results showed that APOE4 carriers who also used HRT had better cognition and higher brain volumes than people not on HRT and non-APOE4 carriers.

Dr Rasha Saleh, from UEA’s Norwich Medical School, said: “We found that HRT use is associated with better memory and larger brain volumes among at-risk APOE4 gene carriers.

“The associations were particularly evident when HRT was introduced early - during the transition to menopause, known as perimenopause.

“This is really important because there have been very limited drug options for Alzheimer’s disease for 20 years and there is an urgent need for new treatments.

“The effects of HRT in this observation study, if confirmed in an intervention trial, would equate to a brain age that is several years younger.”

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Prof Minihane said the team did not look at dementia cases, but that cognitive performance and lower brain volumes are predictive of future dementia risk.

Prof Michael Hornberger, from UEA’s Norwich Medical School, said: “It’s too early to say for sure that HRT reduces dementia risk in women, but our results highlight the potential importance of HRT and personalised medicine in reducing Alzheimer’s risk.

“The next stage of this research will be to carry out an intervention trial to confirm the impact of starting HRT early on cognition and brain health.

“It will also be important to analyse which types of HRT are most beneficial.”

The discovery comes days after US Food and Drug Administration (FDA) granted accelerated approval for the use of the Alzheimer’s drug, lecanemab, in patients with mild cognitive impairment.

It is not yet available on the NHS but, if approved by UK regulators, it would be the first new drug Alzheimer’s drug in 20 years and the first to treat the underlying cause of the disease.

Lecanemab, a monoclonal antibody which is given by infusions every two weeks, clears amyloid plaques from the brain - protein deposits which are believed to set off a chain reaction that damages brain function.

Clinical trials showed that lecanemab slowed the onset of symptoms such as memory decline by around 18 months if administered in the early stages of the disease.