Starting hormone replacement therapy soon after Menopause begins may be better for brain health than taking it later, a study suggests. Researchers found women who experienced premature menopause, before the age of 40, were at higher risk of Alzheimer’s disease.

But those who started HRT around its onset had lower levels of toxic proteins in their brains, compared with women who waited at least five years.

Dr Rachel Buckley, of Massachusetts General Hospital in the US, said: “HRT is the most reliable way to ameliorate severe menopause symptoms, but over the last few decades, there has been a lack of clarity on how HRT affects the brain.

“We found the highest levels of tau, a protein involved in Alzheimer’s disease, were only observed in hormone therapy users who reported a long delay between age at Menopause Onset and their initiation of the therapy.”

Studies looking at HRT and dementia risk have produced conflicting results.

Some have suggested HRT could have a protective effect, while others indicated it could increase the danger.

Dr Gillian Coughlan, also of the MGH, said it was possible the drugs had negative effects on cognition, but only when started years after menopause.

She added in the journal JAMA Neurology: “Up to 10 percent of women experience premature or early menopause, and our findings ­suggest earlier age at ­menopause may be a risk ­factor for dementia.

“These observational findings support clinical guidelines that state HRT should be given close to menopause onset, but not several years after.”

Alzheimer’s UK urged women not to be put off taking HRT – and to talk to their GP with any concerns.