Women who used hormone replacement therapy (HRT) for at least a year had about a 10% lower risk of developing dementia during follow-up, according to a UK Biobank study of 183,450 postmenopausal women published in the journal Alzheimer's & Dementia on 27 August 2026. Researchers led by S. Squires tracked participants for a mean of 13.3 years and found the association was strongest in women who had undergone surgical menopause, those carrying the APOE e4 genetic variant linked to Alzheimer's risk, and those who started HRT between the ages of 46 and 56. Women with natural menopause did not show a statistically significant association. The study is observational, comparing outcomes between women who did and did not use HRT rather than assigning treatment at random, so it cannot show that HRT itself caused the lower dementia rates seen in the data.
Why this is not proof of cause and effect
The authors were explicit that reverse causation or confounding could not be excluded, particularly among older women, since healthier women may be more likely to be prescribed or to continue HRT in the first place. The study relied on broad categories of HRT rather than detailed drug and dose records, may have missed some milder dementia cases, and drew on a UK Biobank cohort that is not fully representative of the UK population by ethnicity or socioeconomic background. A separate, smaller study of donated brain tissue, reported in the journal Neurology, found an association between oestrogen-only therapy and fewer Alzheimer's-related changes in the brain, but it also could not establish cause and effect.
What this means for women weighing up HRT
Dementia prevention is not a licensed or established indication for menopausal hormone therapy in the UK, and the study's authors do not suggest starting or continuing HRT on this basis. The findings may help researchers design the larger, longer trials needed to test cause and effect, and may eventually help clinicians judge which patients are most likely to see a protective association, but they do not change NICE guidance on menopause, which weighs HRT's benefits and risks for managing menopausal symptoms rather than preventing dementia. Anyone already using or considering HRT should discuss the current evidence with their GP or a menopause specialist, rather than drawing conclusions from this single observational study.
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