Does MHT Protect Your Brain? What the Science Actually Says

You have probably seen the headlines: hormone therapy protects the ageing brain, or hormone therapy raises dementia risk. Here is where the evidence genuinely stands right now, and why the honest answer is less dramatic.

One of the largest, most comprehensive studies to date found no clear answer either way

A systematic review and meta-analysis published in The Lancet Healthy Longevity in December 2025, one of the largest and most comprehensive analyses on this question so far, pooled data from over one million women across ten studies, led by an international team including Professor Martha Hickey from the University of Melbourne.¹ It found no clear evidence that MHT either raises or lowers dementia risk.¹ The researchers specifically looked for a "right time to start" window and did not find one.¹ Their conclusion is take MHT for your symptoms and quality of life if it is right for you, but do not take it, or avoid it, because of dementia.

Why other studies have found different things

A separate meta-analysis by Dr Lisa Mosconi and colleagues, published earlier in 2025, found that women who used MHT had an approximately 11 percent lower risk of Alzheimer's or dementia overall in pooled observational data, with the benefit appearing strongest for oestrogen-only therapy started in midlife.² This is a credentialled finding, but it comes entirely from observational studies, which cannot rule out the possibility that women who choose to take MHT differ from women who do not in ways that lower dementia risk; healthcare access, education, income, exercise habits, smoking rates and cardiovascular health can all differ between the two groups and independently influence dementia risk, which is one of the central challenges in this kind of research.²

A third source, a large conference presentation not yet published in a peer-reviewed journal, reported a more specific pattern; roughly 22 to 32 percent lower Alzheimer's risk when MHT was started around the time of menopause, but a 38 percent higher risk when started at 65 or older.³ This is what is sometimes called the "timing hypothesis," however, it needs to be treated with caution, even the researcher behind it was direct that this should not be read as a reason to take MHT specifically to prevent Alzheimer's.³

These three sources genuinely disagree, and the disagreement reflects real differences in study design. The Lancet review is newer, pre-registered, and includes formal bias assessment, but it is also honest that the certainty of its underlying evidence ranges from only moderate to very low.¹

Why oestrogen and the brain are connected

Oestrogen receptors are widely distributed throughout the brain, including regions involved in memory, learning and emotional regulation such as the hippocampus and prefrontal cortex. Oestrogen influences communication between brain cells, synaptic plasticity, the brain's ability to adapt and form new connections, glucose metabolism in brain cells, inflammatory pathways, and vascular health. These are well-established biological effects, and they are exactly why researchers continue to investigate whether the timing of oestrogen exposure influences brain ageing. Unfortunately a biological explanation is not the same as clinical proof, the fact that oestrogen affects the brain does not automatically mean MHT prevents dementia.

What about women with early or surgical menopause?

This is an important distinction that deserves its own mention. Women who experience premature ovarian insufficiency before age 40, early menopause before age 45, or surgical removal of the ovaries, face a longer period without ovarian hormones, and this carries different health considerations. Current guidance supports considering MHT until around the average age of natural menopause for these women, unless there is a specific reason it is unsuitable, because early loss of ovarian hormones has broader health consequences beyond brain health alone.

A word on older research you may have heard about

Some of the caution around MHT and dementia traces back to the Women's Health Initiative Memory Study, a large trial from the early 2000s. It is worth knowing that this study looked specifically at women aged 65 and older starting hormone therapy well after menopause, it was never designed to test safety or effects for women entering perimenopause or early menopause.¹ Applying its findings directly to a 48-year-old considering MHT for hot flushes and sleep disruption is a genuine mismatch in the population being studied, and this distinction matters when you are weighing up what you read.

What this means for you

The science here is not yet settled, it is simply where high-quality research currently sits. What is settled is this, MHT remains a legitimate, well-evidenced option for managing menopausal symptoms and quality of life, and that decision can be made on its own genuine merits, separate from any promise about future brain protection that the evidence does not yet support. Do not start MHT solely to prevent dementia, and equally, do not avoid appropriate MHT out of fear that it will cause dementia, the current evidence supports neither position.

Three takeaways

1. The largest, most comprehensive study to date found no clear evidence that MHT either raises or lowers dementia risk, and found no specific "right time" window either.

2. Other studies have found different results, but they rely more heavily on observational data or have not yet been peer-reviewed, the Lancet review carries the most weight of the three.

3. MHT is a legitimate choice for managing menopausal symptoms, that decision does not need to hinge on an unproven promise of dementia prevention, and women with early or surgical menopause have their own distinct considerations worth discussing directly with their GP.

This is not your body failing you. It is your body changing, and asking for a different kind of support.

This information is educational only and does not constitute personal medical advice. Always consult a qualified health professional about your individual circumstances. © Menopause Hub 2026.

REFERENCES

1. Melville M, He L, Desai R, et al. Menopause hormone therapy and risk of mild cognitive impairment or dementia: a systematic review and meta-analysis. The Lancet Healthy Longevity. 2025 Dec 22:100803.

2. Mosconi L, Andy C, Nerattini M, et al. Systematic Review and Meta-analysis of MHT and the Risk of Alzheimer's Disease and All-cause Dementia: Effects of MHT Characteristics, Location, and APOE-4 Status. Current Obstetrics and Gynecology Reports. 2025;14(1):6.

3. Vaibhav FNU, et al. Timing-dependent effects of estrogen therapy on Alzheimer's disease risk in postmenopausal women: a comprehensive meta-analysis. Presented at the American Neurological Association Annual Meeting 2025.