For years, women have heard conflicting messages about hormone replacement therapy. It helps hot flashes. It may affect heart health. Risks depend on age, timing and medical history.
Now there’s another question on the table: Could hormone therapy also influence dementia risk?
A major new study involving more than 183,000 women suggests the answer may depend partly on when treatment begins.
HRT users had a lower dementia risk
Researchers analyzed data from 183,450 postmenopausal women participating in the UK Biobank and followed them for an average of more than 13 years.
During that time, 3,948 women were diagnosed with dementia, including 1,993 cases of Alzheimer’s disease.
According to the study published in Alzheimer’s & Dementia, women who had used hormone replacement therapy for at least one year had a 10% lower risk of developing dementia from any cause compared with women who had not used HRT.
The association wasn’t identical for everyone.
And that’s where the research gets especially interesting.
Timing appeared to matter
The strongest association was seen among women who started HRT between ages 46 and 56.
That finding adds to growing interest in the idea that when hormone therapy begins may be just as important as whether a woman uses it at all.
Menopause produces a dramatic decline in estrogen, and estrogen affects far more than the reproductive system.
Estrogen receptors are found throughout the brain, and the hormone has been studied for its possible effects on inflammation, blood vessels, glucose metabolism and nerve cells.
Researchers have long wondered whether losing estrogen during menopause could help explain at least part of the difference in dementia rates between men and women.
But previous research into HRT and dementia has produced conflicting results.
The new findings suggest one reason may be that women shouldn’t necessarily be studied as one enormous group. Age at treatment, type of menopause, genetics and lifetime estrogen exposure may all matter.
Women with surgical menopause saw an even larger association
One group stood out.
Women who had undergone surgical menopause and used HRT had a 26% lower risk of dementia compared with nonusers.
Surgical menopause can occur when both ovaries are removed, causing estrogen levels to drop abruptly rather than gradually.
Women with lower lifetime exposure to their own estrogen also appeared to experience a stronger association between HRT and lower dementia risk.
Researchers additionally found stronger associations among women carrying the APOE4 gene variant, one of the most important known genetic risk factors for Alzheimer’s disease.
As coverage of the study explained, these differences could eventually help researchers identify which women are most likely to experience long-term cognitive benefits—or risks—from hormone therapy.
This does not mean HRT prevents Alzheimer’s
This is the most important caveat in the entire story.
The study found an association. It did not prove that hormone therapy prevented dementia.
This was an observational study, not a randomized clinical trial.
Women who use HRT can differ from women who don’t use it in ways that are difficult to completely account for.
For example, HRT users in the study had higher average education levels than nonusers. Education itself has been associated with dementia risk.
Researchers adjusted for numerous factors, including age, education, smoking, blood pressure, BMI, cholesterol and diabetes, but observational research can never completely eliminate the possibility that other differences influenced the results.
Save this article
Enter your email address and we'll send it straight to your inbox.
That’s why the findings shouldn’t be interpreted as a reason to start HRT specifically to prevent dementia.
You May Want to Read: Alzheimer’s or Dementia? These Powerful Distinctions Matter The Most
The history of HRT has been complicated
Millions of women used hormone therapy before concerns about breast cancer, cardiovascular disease and other health risks led to a dramatic decline in prescribing in the early 2000s.
The conversation has evolved considerably since then.
Researchers now understand that the risks and benefits of hormone therapy aren’t necessarily the same for a 50-year-old experiencing new menopausal symptoms and a woman beginning treatment decades after menopause.
Type of hormone, dose, route of administration, age, medical history and timing can all influence the equation.
That’s one reason sweeping statements declaring HRT either “good” or “bad” are increasingly giving way to more individualized discussions.
The new dementia research fits squarely into that shift.
Your genes may eventually become part of the conversation
The APOE4 finding is particularly intriguing.
Having one or two copies of the APOE4 variant increases the risk of developing Alzheimer’s disease, although carrying the gene certainly doesn’t mean someone will develop dementia.
In this study, the association between HRT and reduced dementia risk was stronger among APOE4 carriers.
That raises the possibility that future menopause treatment could become more personalized based on genetics and hormonal history.
We’re not there yet.
The study’s authors say additional research is needed to determine whether HRT itself is responsible for the differences they observed and which forms of hormone therapy might matter.
What should women do with this information?
For women already considering HRT to manage hot flashes, night sweats, sleep disruption or other menopausal symptoms, dementia risk may eventually become another piece of a much larger conversation.
For now, however, this study isn’t enough to recommend hormone therapy as a dementia-prevention strategy.
HRT has potential benefits and risks that vary significantly from one person to another.
Women shouldn’t start, stop or change hormone therapy because of one study. A healthcare professional who knows a patient’s age, menopause history, family history and cardiovascular and breast cancer risk can help evaluate the bigger picture.
Final word
Perhaps the most important message from this research isn’t that HRT prevents dementia. We don’t know that.
It’s that the relationship between menopause, estrogen and the aging brain may be far more individualized than researchers once believed.
A woman who experiences surgical menopause at 45 may not have the same biological circumstances as someone who reaches natural menopause at 53. A woman carrying APOE4 may not respond exactly like someone who doesn’t. And beginning hormone therapy near menopause may be fundamentally different from beginning it many years later.
The new study doesn’t settle the debate over HRT and dementia.
But it does suggest we may have been asking too simple a question. Instead of asking whether HRT is good or bad for the brain, researchers may need to ask: For whom—and when?
