Hormone replacement therapy to treat menopausal symptoms is not linked to an increased risk of developing dementia regardless of hormone type, dose or duration, a large UK study has concluded.

The researchers said the analysis of data from more than 110,000 women aged over 55 with a diagnosis of dementia and almost 500,000 controls would provide clarity where findings had been inconsistent.

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However, there was a slight increased association of developing Alzheimer’s disease in women who had used oestrogen-progestogen treatments for five years or more, the researchers reported in the BMJ.

Previous research had been conflicting. The Women’s Health Initiative Memory Study, a large HRT trial, reported an increased risk of dementia in those on oestrogen-progestogen prescriptions and a large Finnish study reporting increased risk of Alzheimer’s with both oestrogen-only and oestrogen-progestogen treatments.

In the latest research, teams from the Universities of Nottingham, Oxford and Southampton used two large primary care databases to look at HRT prescriptions in the previous three years in women diagnosed with dementia and controls matched by age and general practice.

The study – which also took into account family history, smoking, alcohol consumption, pre-existing conditions, and other prescribed drugs – found 14% of both women with dementia and controls had used HRT in the three years previously.

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In a subgroup analysis of those aged under 80 years who had been taking oestrogen-only therapy for 10 years or more, the researchers found a slightly decreased risk of dementia. 

For those with a specific diagnosis of Alzheimer’s disease, a slight increase in risk associated with oestrogen-progestogen therapy rose gradually with each year of exposure, reaching an average 11% between 5 and 9 years and 19% for use of 10 years or more – equivalent to five and seven extra cases per 10,000 woman years, respectively.

The analyses provide the most detailed estimates of risk for individual treatments to date and the findings are in line with existing concerns in guidelines about long-term exposure to combined HRT, the researchers said.

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‘The findings will be helpful to policy makers, doctors, and patients when making choices about hormone therapy,’ they concluded.

‘The primary indication for hormone therapy continues to be the treatment of vasomotor symptoms, and the current study should provide reassurance for women and their providers when treatment is prescribed for that reason,’ they added.