A large new study is adding fresh evidence to one of the most debated questions in women’s health: does hormone replacement therapy (HRT) affect the risk of developing dementia later in life?
The research, published in the journal Alzheimer’s & Dementia in late August 2026, followed over 183,000 postmenopausal women from the UK Biobank for an average of 13 years. It found that women who used HRT had a modestly lower overall risk of dementia, but the size of that benefit varied considerably depending on who they were and when they started treatment.
Researchers tracked participants for more than 2.4 million person-years and identified nearly 4,000 new dementia diagnoses. Overall, women who had used HRT for at least a year were about 10% less likely to develop dementia of any kind compared with women who never used it. The protective association was stronger for Alzheimer’s disease specifically, with roughly a 16% lower risk, but there was no statistically meaningful link between HRT and non-Alzheimer’s forms of dementia.
The headline figure, a 10% overall risk reduction, masks much bigger effects in certain subgroups:
This aligns with a broader body of research that has produced conflicting results over the years. The Women’s Health Initiative Memory Study, the only randomised controlled trial to look directly at dementia as a primary outcome, actually found an increased dementia risk among women over 65 who used combined oestrogen plus progestin therapy. Other observational studies have found protective effects, and at least one earlier UK Biobank analysis with a shorter follow-up period found no effect at all.
The authors of the new study argue that these seemingly contradictory results may be explained by exactly the kind of subgroup differences they identified: the type of menopause a woman experienced, her genetic risk profile, how long she was naturally exposed to oestrogen, and, critically, how old she was when she started HRT. According to coverage of the study by News-Medical, further sensitivity analyses that excluded women diagnosed close to baseline and examined other possible modifiers supported the robustness of these findings.
Despite the promising numbers, both the study authors and outside experts urge caution. This was an observational study, meaning it can show an association but cannot prove that hormone therapy directly prevents dementia.
According to reporting in Women’s Health magazine, Lauren Streicher, MD, a clinical professor of obstetrics and gynaecology at Northwestern University’s Feinberg School of Medicine, points to “healthy user bias” as a likely contributor. Women who choose to use, and who have access to, hormone therapy tend to be healthier overall and may already carry a lower baseline risk of dementia for reasons unrelated to the hormones themselves.
Clifford Segil, DO, a neurologist at Providence Saint John’s Health Center, notes that women on HRT often simply feel better, which could translate into more brain-healthy habits like exercise and better sleep, behaviours that could account for some of the observed benefit.
The study itself also has real limitations. It didn’t have data on the specific type of hormone therapy used (oestrogen-only versus combined oestrogen-progestogen), the dose, or how it was administered (oral, topical or vaginal), all factors known to matter for both dementia and cardiovascular risk. As reported by EMJ Reviews, study author Professor David Llewellyn of the University of Exeter Medical School noted that rather than simply asking whether HRT affects dementia risk, the research helps identify which women are most likely to benefit, and when, laying groundwork for more personalised approaches to women’s brain health. The UK Biobank population also skews towards people of European descent and more socioeconomically advantaged backgrounds, which may limit how broadly the findings apply.
Hormone therapy remains, first and foremost, a treatment for menopause symptoms like hot flushes and sleep disruption. This study adds meaningful evidence that HRT, particularly when started in the mid-40s to mid-50s, and especially for women who’ve had surgical menopause or carry APOE ε4, is associated with a lower risk of later dementia.
But researchers stop short of recommending hormone therapy as a dementia-prevention strategy on its own. Confirmation in a randomised controlled trial is still needed before this translates into new clinical guidance.
If you’re weighing whether to start or continue hormone therapy, the current evidence suggests it’s worth a conversation with your doctor about your personal risk factors, including family history, genetic risk and type of menopause, rather than a decision based on dementia risk alone.
