Could HRT Lower Dementia Risk? New Research Suggests Timing May Matter

New Research: HRT use was linked to lower dementia risk, but timing and individual factors may matter

HRT, also known as hormone replacement therapy, is used by many women to help manage symptoms during the menopause transition. Some begin treatment during perimenopause, often in their 40s, while others may consider starting it much later, after menopause.

For many women, HRT can be a highly effective treatment, particularly for symptoms such as hot flashes and night sweats. But, like any medication, it isn’t a universal treatment. Whether it is appropriate depends on the individual, including their symptoms, age, medical history, and the type of hormone therapy being considered.

HRT has also been surrounded by decades of debate, particularly around its safety and possible long-term effects. 

Over the years, advice around HRT has changed considerably, particularly when it comes to when women should start treatment, how long they should take it, and how the balance of benefits and risks may change with age. It’s no wonder many women are left unsure about what HRT could mean for their long-term health.

What is HRT and What Does It Do?

Hormone replacement therapy (HRT) is a treatment used to replace hormones that fall to lower levels as women approach and go through menopause.

There are two main types of HRT: estrogen-only HRT and combined HRT, which contains estrogen and a progestogen. Which type is generally recommended depends on whether a woman still has her uterus. Women who have had a hysterectomy can usually take estrogen-only HRT, while women who still have their uterus generally need combined HRT because the progestogen helps protect the lining of the uterus.

HRT can be highly effective at relieving menopause symptoms, including hot flashes, night sweats, sleep problems, and vaginal symptoms. It can also help protect against the bone loss that accelerates after menopause.

What Did the Researchers Investigate?

Previous research into HRT and dementia has produced conflicting results, leaving questions about whether hormone therapy might influence dementia risk and, importantly, whether the timing of treatment makes a difference.

The researchers wanted to look beyond HRT use alone. They wanted to investigate whether the relationship between HRT and dementia differed depending on when a woman started treatment and whether she experienced natural or surgical menopause. They also looked at whether lifetime estrogen exposure and APOE ε4 status, a genetic factor associated with Alzheimer’s disease, influenced the results.

To do this, they analyzed data from 183,450 postmenopausal women in the UK Biobank, following them for an average of 13.3 years.

What Did the Study Find?

Over the course of the study, 3,948 women developed dementia—about half (1,993) with Alzheimer’s and the other half (1,955) with other or unspecified types of dementia. Overall, women who used HRT for at least a year were 10% less likely to develop dementia than those who took it for less than a year or not at all.

However, the picture became much clearer when researchers looked at specific groups of women.

The Type of Menopause Appeared to Matter

The lower risk associated with HRT was most noticeable in women who had undergone surgical menopause (such as having their ovaries removed), who had a 26% lower risk of dementia. For women who went through menopause naturally, HRT was linked to only a slight 6% risk reduction—a difference small enough that it could have been down to chance.

Timing was Another Major Factor

The study found that starting age appeared to make a difference. Overall, starting HRT between the ages of 46 and 50 was linked to a 13% lower risk of dementia, while starting between 51 and 56 was linked to a 23% lower risk. However, this age pattern shifted depending on whether a woman went through natural or surgical menopause, suggesting that age is only part of the puzzle.

Lifetime Estrogen Exposure also Played a Role

Researchers also measured each woman’s total lifetime estrogen exposure—the years between her first period and menopause. They found that women with under 37 years of natural estrogen exposure had a 16% lower risk of dementia with HRT, a noticeably stronger association than in women with longer natural estrogen exposure.

The Role of Genetics

Genetics was another factor researchers explored. The team checked whether carrying APOE ε4 (a known Alzheimer’s risk gene) altered the results. They found that women with the gene who used HRT had a 13% lower risk of dementia.

However, the numbers weren’t strong enough to confirm that the gene itself makes HRT more effective. It’s a noteworthy clue, but not enough to show that women with APOE ε4 experience a greater reduction in dementia risk with HRT.

Alzheimer’s Disease Showed a Stronger Association

When the researchers looked specifically at Alzheimer’s disease, HRT use was associated with a 16% lower risk overall.

Again, the association differed depending on the type of menopause. Women who experienced natural menopause had an 11% lower risk of Alzheimer’s, while those who had surgical menopause had a 32% lower risk.

For other or unspecified forms of dementia, however, HRT was not associated with a significant risk reduction overall.

What Does This Mean for You?

These findings show that the link between HRT and dementia is not as simple as it may sound. The timing of HRT, whether a woman experienced natural or surgical menopause, and her lifetime estrogen exposure all appeared to shape the results.

While the study found an association between HRT and lower dementia risk, it does not prove that HRT caused the reduction—so women should not start HRT specifically to prevent dementia. Instead, the findings highlight the importance of a personalized approach rather than treating HRT as a one-size-fits-all therapy.

Study Limitations

Despite the large number of women included and the long follow-up period, there are some important limitations to consider.

Most importantly, this was an observational study, which means it can identify associations but cannot prove that HRT caused the lower dementia risk. Other differences between women who chose to use HRT and those who did not may have influenced the results.

The data lacked detailed information on doses, delivery methods (patches vs. pills), or hormone combinations. This matters because estrogen-only and combined HRT, as well as oral and transdermal treatments, may not have the same effects.

The UK Biobank participants were also predominantly White and generally healthier and more affluent than the wider population, so the findings may not apply equally to all women.

Finally, although the overall study was large, dividing women into smaller groups—for example, by menopause type, HRT starting age, or genetic status—means some of those individual findings are less certain.

The Lillepin Takeaway

This research adds another piece to the complicated relationship between HRT and long-term brain health. While HRT use was associated with a lower risk of dementia overall, the results suggest that when a woman starts HRT, how she experiences menopause, and her lifetime exposure to estrogen may all matter.

Perhaps most importantly, the findings show why HRT and dementia shouldn’t be viewed as a simple question of whether HRT is “good” or “bad” for the brain.

For now, this study does not provide evidence that women should take HRT to prevent dementia.

It does, however, offer valuable clues about which factors may need to be considered in future studies—and why a more individualized approach to HRT research matters.