Hysterectomy, ovary removal and dementia risk: what the research actually shows

Short answer: The widely repeated claim that removing your ovaries raises your dementia risk is based on real research — but the largest analysis ever done on the question, pooling 233,802 women, found no excess dementia risk from surgical menopause compared with natural menopause. What predicted risk in that analysis wasn't the surgery. It was how early menopause happened, by any route. Women whose menopause came before 40 had a higher rate of dementia whether it arrived naturally or surgically; women whose menopause came at a typical age had the same rate whether or not surgery caused it. That is a meaningfully different — and considerably less alarming — story than the one circulating, and it points at something you can actually do something about.

This is educational, not medical advice. Decisions about hysterectomy, ovary removal and hormone therapy belong with your gynaecologist or GP, who knows why the surgery was recommended and what your other risks are. Nothing here is a reason to delay or decline a procedure your doctor has advised.

Where the frightening version came from

The claim traces back to a genuinely important 2007 study from the Mayo Clinic. Researchers followed women in Olmsted County, Minnesota who had one or both ovaries removed before menopause for non-cancer reasons between 1950 and 1987 — 813 with one ovary removed, 676 with both — and compared them against 1,472 age-matched women who hadn't had the surgery.

They found that women who had an ovary removed before menopause had a 46% higher rate of cognitive impairment or dementia (hazard ratio 1.46, 95% CI 1.13–1.90). And crucially: the younger the surgery, the higher the risk, a trend so strong it was unlikely to be chance (p < 0.0001).

The proposed explanation was straightforward. The ovaries are the main source of oestrogen before menopause, oestrogen appears to have protective effects in the brain, and removing them in a woman's 30s means decades of oestrogen exposure she would otherwise have had simply doesn't happen.

(Rocca WA, Bower JH, Maraganore DM, et al., Neurology 2007)

That finding is where "ovary removal causes dementia" comes from. It was a careful study, cited for nearly two decades. But note what it compared: women who had surgery before menopause — often in their 30s and early 40s — against women of the same age who hadn't. It could not test whether the surgery was the problem, or whether losing ovarian hormones early was.

What the largest analysis found

In November 2024, researchers pooled five long-running cohorts from Australia, Sweden, England, the UK and the Netherlands: 233,802 women, 3,262 of whom developed dementia. It is by a wide margin the biggest attempt to separate those two explanations.

The results:

Type of menopause — essentially no difference.

A hazard ratio of 1.00 means no difference. Both of these sit on it.

Age at menopause — a clear gradient.

The authors' conclusion is one sentence, and it's the one worth carrying away: "Women who experience menopause before the age of 40 years have a higher risk of dementia irrespective of type of menopause."

(Dobson AJ, Xu Z, Wilson LF, et al., "Menopause age and type and dementia risk: a pooled analysis of 233,802 women," Age and Ageing, 19 November 2024)

A separate 2025 analysis of 147,119 women in UK Biobank pointed the same way. Bilateral oophorectomy (HR 0.87) and hysterectomy (HR 1.10) were not significantly associated with dementia — while natural menopause before 45 was (HR 1.31, p = 0.007), and every additional year before menopause was associated with slightly lower risk.

One honest limit on that second study, because it matters enormously to anyone reading this page while facing surgery: that analysis covered surgery at age 50 or older. It tells you nothing about oophorectomy in your 30s. Don't read it as reassurance about early surgery — read it as one more piece of evidence that surgery at a normal menopausal age doesn't appear to carry extra risk.

(Geraets A, Ford K, May P, Kidd E, Leist A, BMJ Public Health, 27 July 2025)

Both things can be true — and the age threshold is where they meet

It would be easy to read the 2024 pooled analysis as debunking the 2007 one. It doesn't. It reframes it.

A brain-imaging study published in December 2024 makes the point precisely. Mayo Clinic researchers scanned 231 women a median of 23 years after surgery, splitting them into those who had both ovaries removed before 46, those who had it at 46–49, and women who hadn't.

The early group showed measurable differences decades later: thinner entorhinal cortex — one of the first regions affected in Alzheimer's disease — plus higher amyloid levels at older ages and higher tau where amyloid was already elevated.

The group who had the same surgery at 46 to 49 showed no significant differences from women who hadn't had it at all.

(Kantarci K, Kapoor E, Geske JR, et al., Alzheimer's & Dementia, 23 December 2024)

That's a small, cross-sectional study measuring brain markers rather than dementia itself, so it isn't proof. But it lines up with the pooled data almost too neatly. Put the three studies together and a coherent picture emerges:

• Losing ovarian hormones well before the usual age — roughly, before the mid-40s — is associated with changes in the brain and with higher dementia rates decades later.
• The surgery itself is not the mechanism. Menopause arriving early is, whether surgery caused it or nothing did.
• Hysterectomy with the ovaries left in place — the more common operation — shows little or no association in the large datasets.

Which means the question that matters isn't "did I have surgery?" It's "at what age did my ovarian hormones stop?"

If your menopause came early — surgically or naturally

This is where the research turns into something actionable, and where you need a clinician rather than an article.

For premature menopause (before 40) or early menopause (before 45) — however it happened — professional guidance is generally to consider hormone therapy at least until around the average age of natural menopause, about 52, unless there's a reason you shouldn't take it. The Menopause Society's 2022 position statement is explicit that women with premature or early menopause face higher risks of bone loss and heart disease from prolonged oestrogen deficiency, and that hormone therapy is recommended in this group absent contraindications.

Two things must be kept apart here, because they get conflated constantly:

1. Hormone therapy after premature or early menopause is standard care — replacing hormones you'd normally still have, for bone, cardiovascular and symptom reasons. That is a real, mainstream recommendation, and if it applies to you it's worth a specific conversation with your doctor.
2. Hormone therapy is not a dementia-prevention treatment. The World Health Organization's 2026 risk-reduction guidelines recommend against hormone therapy taken solely to reduce dementia risk. The evidence doesn't support it for that purpose, and in the 2025 UK Biobank analysis lifetime hormone therapy use was associated with slightly higher dementia incidence (HR 1.13) — a borderline, confounding-prone observational finding that shouldn't frighten anyone, but certainly doesn't support taking it for your brain.

So: if you had early menopause, ask about hormone therapy. Ask about it for the reasons it's actually indicated. Don't ask for it as a dementia strategy, and be sceptical of anyone selling it that way. What the WHO now says about lowering dementia risk covers the broader list of things the evidence doesn't support.

What early menopause is actually a signal to do

Here's the part that gets lost in the anxiety. Even taking the largest number in the data — a 47% higher relative rate of dementia for menopause before 40 — that factor sits alongside a long list of others, and most of the others are ones you can change.

The 2024 Lancet Commission links around 45% of dementia cases worldwide to 14 modifiable risk factors. Age at menopause isn't on that list. High blood pressure, diabetes, smoking, hearing loss, physical inactivity, depression, social isolation, high LDL cholesterol and untreated vision loss are — and every one of them is open to intervention.

There's a specific connection worth knowing about too. The 2025 UK Biobank analysis found that a small share of the link between earlier menopause and dementia ran through blood-sugar control — HbA1c mediated up to 4.7% of the effect. That's a modest fraction, but it's a concrete, measurable, treatable pathway. The authors' own recommendation was that the metabolic profile of women who go through natural menopause early should be monitored. In practice: a conversation with your doctor about blood sugar, blood pressure and cholesterol, and regular checks.

The most useful reframe available: an early menopause isn't a verdict. It's a reason to be a bit more deliberate about blood pressure, blood sugar, cholesterol, hearing, activity and sleep than someone whose menopause arrived at 51 — starting earlier, rather than doing anything different.

And if what actually brought you here is brain fog in your 40s or after surgery, that's a different question with a much more reassuring answer: menopause brain fog vs. dementia.

Questions worth taking to your gynaecologist

If you're facing a hysterectomy or oophorectomy:

• Do my ovaries need to come out, or can they be conserved? (For non-cancer indications before menopause, this is often a genuine choice — and the large datasets suggest hysterectomy with ovaries conserved carries little dementia signal.)
• If they do need to come out and I'm under 45, what's the plan for hormone therapy afterwards, and until what age?
• What are we treating, and what happens if we don't?

If you've already had surgery, or went through menopause early naturally:

• Given my age at menopause, should I be on hormone therapy, and for how long?
• Should we be checking blood pressure, blood sugar and cholesterol more actively?
• Is there anything in my personal or family history that changes this picture?

Notice that none of those is a dementia question. That's deliberate: the evidence-based responses to early menopause are bone, heart and metabolic ones — which happen to be the same levers that show up in the dementia research anyway.

Check where you actually stand

If early menopause is part of your history, the useful next step isn't worrying about a number you can't change. It's finding out which of the changeable factors apply to you.

More on the broader picture: can you reduce your dementia risk? and check your dementia risk.

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This article is educational and is not medical advice, diagnosis, or treatment. The studies cited describe findings in general populations, not any individual. Solenna is not a medical device and does not diagnose, prevent, treat, or cure Alzheimer's disease or any other condition. Risk reduction means lowering probability, not eliminating it; individual results vary and no outcome is guaranteed. Decisions about gynaecological surgery, hormone therapy or menopause management should be made with a qualified clinician who knows your history.