Her mother had Alzheimer's. So when, at 49, she started losing words mid-sentence and walking into rooms with no idea why, menopause didn't cross her mind. Her mother did. She spent months quietly running through the possibilities at 3am and told no one.
When she finally saw her GP, the pattern fitted perimenopause and her memory tests were normal. A couple of years later, on HRT and sleeping again, the fog had mostly lifted. The bigger question stayed with her, though: was menopause changing her long-term risk of dementia, and should HRT be part of protecting her brain?
Online, the answers range from "HRT protects your brain" to "HRT causes dementia". The evidence supports neither, and the truth is more useful than both.
This is usually the fear underneath the question, so it's worth dealing with first.
Problems with memory, word-finding and concentration are very common in perimenopause. They are real, they can be frightening, and in the large majority of women they are not a sign of dementia. The best long-term evidence comes from the American SWAN study, which followed thousands of women through the menopause transition with repeated memory tests. Performance on some tests dipped during perimenopause and then recovered after menopause. Dementia does the opposite: it gets steadily worse.
Brain fog is also driven by things that can be treated: broken sleep, night sweats, low mood and anxiety. Menopause brain fog covers that in detail.
The signs that are different, and worth seeing your GP about, include:
Dementia is now the leading cause of death in the UK, and more women than men live with it. Part of that is simply that women live longer. But researchers have long suspected that the fall in oestrogen at menopause might play a part too, because oestrogen acts on the brain in many ways, including on blood flow and how brain cells use energy.
There's some evidence for the idea. Women who go through menopause very early, especially after surgery to remove both ovaries before 45, appear to have a higher risk of dementia later. It's one of several reasons NICE recommends HRT for women with premature ovarian insufficiency, menopause before 40, until at least the usual age of menopause. The British Menopause Society advises the same for women whose menopause comes between 40 and 45. See early menopause before 45 and surgical menopause.
But "oestrogen matters to the brain" is not the same as "taking HRT prevents dementia". That is where the evidence gets complicated.
The only large randomised trial was in older women, and it found harm. The Women's Health Initiative Memory Study, published in 2003, gave women aged 65 and over either combined HRT, using an older oral oestrogen with a synthetic progestogen, or a placebo. Those on HRT were about twice as likely to be diagnosed with probable dementia, roughly 23 extra cases for every 10,000 women each year. These women started HRT on average around 71, long after menopause.
A large UK study, on the other hand, found no overall increase. Researchers at the University of Nottingham, led by Yana Vinogradova, compared more than 118,000 women with dementia with nearly 500,000 without, using GP records. After adjusting for other factors, they found no overall link between HRT and dementia. There was a small increase in Alzheimer's disease in women who had used combined HRT for five years or more.
A Danish study then found a link even in younger users. A nationwide study published in the BMJ in 2023 compared 5,589 women with dementia with 55,890 without. Women who had used combined HRT had a 24% higher rate of dementia, including those who started it at 55 or younger. The longer they had used it, the higher the rate.
The last two studies are observational. They show associations, not cause and effect. Women who take HRT differ from women who do not in many ways, including how severe their symptoms were, and severe symptoms themselves may be linked with later brain health. The editorial published alongside the Danish study warned that this kind of confounding could produce a false signal. Neither study can tell us what HRT does to an individual woman's risk.
Many researchers suspect that when HRT is started matters. The idea, known as the critical window hypothesis, is that oestrogen may help or be neutral when it is started around menopause, and may be unhelpful or harmful when started many years later in a brain that has already changed. It would explain why the trial in women over 65 found harm.
It is a plausible idea, and it may turn out to be right. But it has not been proven in a trial large enough or long enough to measure dementia, and the Danish study did not find the reassurance in younger women that the hypothesis would predict.
NICE's menopause guideline, updated in 2024 after a full review of the dementia evidence, tells doctors to explain to women that the likelihood of HRT affecting their risk of dementia is unknown.
In practice, that means two things. You should not start HRT in the hope of preventing dementia, because there is no good evidence that it does. And you should not stop or avoid HRT that is helping your symptoms purely out of fear of dementia, because the evidence does not show that either. The decision should rest on the benefits and risks that are better understood. The truth about HRT research sets those out.
This is where the evidence is much stronger, and much more useful.
In 2024, the Lancet Commission on dementia, an international group of leading researchers, concluded that around 45% of dementia cases could in theory be prevented or delayed by tackling 14 risk factors across life. Most of them matter most in midlife, which is exactly the age at which women go through menopause:
Most of these are the same things that protect your heart, because what's good for blood vessels is good for the brain.
Does menopause cause dementia?
No. Menopause is not a cause of dementia, and the memory problems of perimenopause usually improve afterwards. Very early menopause, especially after removal of both ovaries before 45, has been linked to higher dementia risk later.
Does HRT prevent dementia?
There's no good evidence that it does. NICE advises that the effect of HRT on dementia risk is unknown, and HRT should not be started to prevent dementia.
Does HRT increase dementia risk?
Combined HRT started at 65 or over increased dementia in one trial. Studies of women starting it around menopause are mixed and observational: a large UK study found no overall increase, while a Danish study found a higher rate. Neither proves cause and effect.
Is brain fog a sign of early dementia?
Usually not. Brain fog in perimenopause is common and tends to improve after menopause. See your GP if you get lost in familiar places, repeat yourself often, or others notice changes in your personality or judgement.
What can I do to lower my dementia risk?
Treat high blood pressure and cholesterol, protect your hearing and eyesight, stay active, avoid smoking, keep alcohol moderate and stay socially connected. Midlife is when these changes matter most.
Should I stop HRT because of dementia worries?
Not on that basis alone. Discuss your overall benefits and risks with your prescriber, including how long you have used HRT and what you are using it for.
Sources: Shumaker SA et al., Estrogen plus progestin and the incidence of dementia and mild cognitive impairment in postmenopausal women: the Women's Health Initiative Memory Study, JAMA 2003;289(20):2651-62 · Vinogradova Y et al., Use of menopausal hormone therapy and risk of dementia: nested case-control studies using QResearch and CPRD databases, BMJ 2021;374:n2182 · Pourhadi N et al., Menopausal hormone therapy and dementia: nationwide, nested case-control study, BMJ 2023;381:e072770 · Livingston G et al., Dementia prevention, intervention, and care: 2024 report of the Lancet standing Commission, Lancet 2024 · Greendale GA et al., Effects of the menopause transition and hormone use on cognitive performance in midlife women (SWAN), Neurology 2009 · National Institute for Health and Care Excellence, Menopause: identification and management (NG23), 2024 · Educational only, not medical advice.
Keep reading: Menopause brain fog · The truth about HRT research · Menopause and heart health · Menopause, hearing and tinnitus · When to start HRT · Take the free Hormone Quiz