HRT Could Lower Dementia Risk - But Timing and Biology Decide Who Benefits Most

New research from the University of East Anglia and the University of Exeter offers some of the strongest evidence yet that hormone replacement therapy (HRT) may help protect the brain - though the benefit isn't spread evenly across all women.

The study, the largest of its kind, followed more than 183,000 postmenopausal women in the UK Biobank over an average of 13.3 years, during which almost 4,000 developed dementia. Overall, HRT users were around 10% less likely to develop dementia and 16% less likely to develop Alzheimer's specifically, compared with women who had never used it.

The effect was far more pronounced in certain groups. Women who had undergone surgical menopause - typically after ovary removal - saw a 26% lower risk of any dementia if they used HRT. Women with naturally lower lifetime oestrogen exposure, whether from late-starting periods or early menopause, also saw a stronger benefit, at around 16% lower risk. Genetics mattered too: the protective association was stronger among carriers of the APOE4 gene variant, the best-known genetic risk factor for Alzheimer's - a group that typically has few established prevention options.

"Dementia affects millions of people worldwide, with women making up almost two thirds of Alzheimer's disease cases," said Professor Anne-Marie Minihane of UEA's Norwich Medical School, who led the study. She points to menopause's effects on brain metabolism, and APOE4's outsized impact in women, as likely explanations for that imbalance - and the motivation for asking whether HRT could help, and for whom.

Timing emerged as a critical factor. Women who started HRT between ages 46 and 56 saw the greatest reduction in dementia risk, lending support to the "critical window" hypothesis - the idea that hormone therapy is more protective when started around the menopausal transition rather than years later. Starting outside that window didn't show the same benefit.

Researchers controlled for age, socioeconomic factors, other health conditions and medication use, to isolate the relationship between HRT and dementia risk from other explanations.

The findings build on earlier UEA research linking HRT use to better memory, cognition and larger brain volumes later in life among APOE4 carriers - adding weight to the idea that hormone therapy's role may extend well beyond managing hot flushes and night sweats.

"Rather than asking simply whether HRT affects dementia risk, we've been able to identify which women are most likely to benefit, and when," said Professor David Llewellyn of the University of Exeter Medical School. "That's the foundation on which genuinely personalised approaches to women's brain health can be built."

Dr Amanda Collis of the BBSRC, which funded the research, echoed that shift toward personalisation: "The findings suggest that HRT could have greater protective benefits for some groups, highlighting the potential for more personalised approaches to prevention."

The study - 'Hormone replacement therapy and dementia risk among postmenopausal women: identifying responsive subgroups in the UK Biobank' - is published in Alzheimer's & Dementia, and points toward a future where HRT prescribing accounts for menopause type, genetic risk, lifetime hormone exposure and age at initiation, rather than a one-size-fits-all approach.