Hormone replacement therapy may be linked to a lower risk of dementia in some women after menopause, according to a large UK study.
Researchers from the University of East Anglia and the University of Exeter found that the association was strongest in certain groups, including women who experienced surgical menopause. The findings suggest that the effects of hormone therapy on the brain may depend on a woman’s biology, genetics and the age when treatment begins.
Dementia affects memory, thinking and the ability to manage everyday life, and Alzheimer’s disease is its most common form. Women account for almost two-thirds of Alzheimer’s cases worldwide. Longer female life expectancy explains part of this difference, but researchers are also studying whether hormonal changes around menopause affect the aging brain.
During menopause, levels of estrogen fall sharply. Estrogen is best known for its role in the reproductive system, but it also affects the brain, blood vessels, bones and metabolism. Scientists have therefore questioned whether replacing some of this lost hormone could influence dementia risk later in life.
Hormone replacement therapy, usually called HRT, is mainly used to relieve menopausal symptoms such as hot flashes, night sweats and vaginal dryness. Depending on a woman’s circumstances, treatment may contain estrogen alone or estrogen combined with another hormone. HRT has known benefits and risks, so decisions about treatment are normally based on an individual’s symptoms, age and medical history.
For the new research, the team analyzed information from 183,450 postmenopausal women in the UK Biobank. The women were followed for an average of 13.3 years, making this the largest study of its kind so far. Nearly 4,000 participants developed dementia during the follow-up period.
The researchers compared women who had used HRT for at least one year with women who had never used it. They also considered factors that could affect both HRT use and dementia risk, including age, socioeconomic circumstances, other medical conditions and medication use. Overall, women who had used HRT were about 10% less likely to develop any form of dementia.
The difference was larger for Alzheimer’s disease. Previous HRT users had a 16% lower risk of developing Alzheimer’s than women who had never used hormone therapy. However, the researchers found that the association varied considerably between different groups of women.
One of the strongest findings involved surgical menopause, which can occur when both ovaries are removed. Unlike natural menopause, where hormone levels usually change over time, removal of the ovaries can cause a sudden and substantial fall in estrogen. Women with surgical menopause who used HRT had about a 26% lower risk of dementia than comparable women who did not use it.
Women with naturally lower lifetime exposure to estrogen also appeared to benefit more. This group included women who started menstruating later or reached menopause earlier, giving them fewer reproductive years with naturally produced estrogen. Among these women, HRT use was associated with about a 16% lower risk of dementia.
Genetic differences also appeared to matter. The protective association was stronger among women carrying APOE4, a gene variant that is one of the most important known genetic risk factors for Alzheimer’s disease. APOE4 does not guarantee that someone will develop dementia, but carrying the variant increases the likelihood.
Timing may be another important piece of the puzzle. Women who started HRT between ages 46 and 56 showed the greatest reduction in dementia risk. This supports the idea of a possible ‘critical window’ in which hormone therapy may have different effects when started around the menopausal transition than when begun much later.
Professor Anne-Marie Minihane of UEA’s Norwich Medical School, who led the research, said the findings show that the relationship between HRT and dementia is not the same for every woman. Professor David Llewellyn of the University of Exeter said identifying who may benefit and when could eventually support more personalized approaches to women’s brain health.
The research was published in the journal Alzheimer’s & Dementia. It builds on earlier work from UEA linking HRT with better memory, thinking ability and larger brain volumes in later life among women carrying APOE4. Together, the studies raise important questions about whether hormone history should be considered more carefully when researchers study dementia prevention.
The results are encouraging, but they should not be interpreted as proof that HRT prevents dementia. This was an observational study, so women were not randomly assigned to receive hormone therapy, and differences between HRT users and nonusers could partly explain the results.
The number of dementia cases was also much smaller than the overall study population, making further confirmation important.
The most valuable part of the study may be its finding that there is no single HRT effect that applies equally to all women. Surgical menopause, lifetime estrogen exposure, APOE4 status and the timing of treatment all appeared to influence the association.
Future clinical studies will be needed before HRT could be recommended specifically for dementia prevention, but the research provides a useful foundation for studying more individualized approaches to menopause and long-term brain health.
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Source: University of East Anglia and University of Exeter.
