Could estrogen use in older women be connected with a healthier brain?
A study of more than 21,000 women found that those who had used estrogen-only hormone therapy later in life had fewer signs of Alzheimer’s disease and were less likely to be diagnosed with dementia.
The result is intriguing, but researchers say it should not change how women use hormone therapy today.
Alzheimer’s disease develops slowly. Long before serious memory loss appears, abnormal proteins can begin accumulating in the brain. Amyloid forms plaques between nerve cells, while tau can form tangles inside cells and is closely linked to nerve damage as the disease advances.
Scientists are interested in factors that might influence this long process. Estrogen has attracted attention because it affects much more than reproduction. The hormone also interacts with the brain, blood vessels, bones, and many other tissues, and estrogen levels fall sharply during the menopausal transition.
Hormone therapy can replace estrogen and is an effective treatment for troublesome menopausal symptoms in appropriately selected women. There are different forms of treatment. Women who have had a hysterectomy may be prescribed estrogen alone, while women with a uterus generally need a progestogen as well to protect the uterine lining.
The relationship between hormone therapy and dementia has been difficult to understand. Past studies have sometimes reached different conclusions, partly because they studied different hormone combinations, doses, ages, and treatment schedules. The age at which therapy begins may be especially important.
In the new study, researchers led by Jennifer Bruno of Stanford Medicine looked specifically at estrogen-only therapy. They analyzed two large datasets that together included 21,462 female participants who had received clinical testing while alive. Follow-up lasted about three to five years and began when participants were approximately 71 years old on average.
Only 1,953 women had used hormone therapy, while 19,509 had not. Importantly, users had started treatment after age 70 on average. This is very different from current practice, in which menopausal hormone therapy is usually started much closer to menopause and generally is not first begun at such an advanced age.
The study went beyond asking whether women eventually received a dementia diagnosis. Researchers also examined evidence of Alzheimer’s disease in the brain itself. A subgroup of 2,959 participants underwent autopsy after death at an average age of 82.
At autopsy, researchers evaluated amyloid-beta plaques, tau tangles, and neuritic plaques. These are important physical signs of Alzheimer’s disease, although the relationship between brain pathology and a person’s symptoms can vary. The team used a combined measure to compare the amount of Alzheimer’s-related pathology between hormone users and nonusers.
The differences were substantial. Among women who had used estrogen-only therapy, 18% showed none of the three Alzheimer’s signs, compared with 10% of women who had not used it. Meanwhile, 40% of hormone users had all three signs, compared with 51% of nonusers.
When the researchers adjusted for age, education, race, genetic factors, and high blood pressure, women who had used hormone therapy had 35% lower odds of Alzheimer’s disease pathology at autopsy. Adjusting for these factors helps make the groups more comparable, but it cannot eliminate every possible source of bias in an observational study.
A smaller group of 728 women also had brain scans or biomarker tests while alive. In hormone therapy users, measurements of amyloid-related proteins in blood and cerebrospinal fluid suggested that less amyloid was being trapped in brain plaques. This biological evidence was broadly consistent with the autopsy findings.
The researchers then examined what happened clinically. Women who had used estrogen-only hormone therapy had 39% lower odds of receiving a dementia diagnosis. They were also less likely to develop signs of memory decline or difficulty carrying out normal daily activities.
The research was published in Neurology. Taken together, the results create a notable pattern: hormone therapy use was associated with better outcomes in clinical assessments, biological markers, and brain tissue. Using several independent measures is valuable because dementia is complex and no single test tells the entire story.
Yet the study cannot answer the most important question: did estrogen cause these differences? The researchers looked back at existing medical information rather than randomly assigning women to take estrogen. Women who received hormone therapy may have been different from nonusers in health, socioeconomic circumstances, medical care, or other ways that also influence dementia risk.
There is also a major gap between the women studied and women considering hormone therapy today. The participants had used treatment under medical practices from earlier decades, and the average starting age was unusually late. Modern recommendations generally focus on treating menopausal symptoms near the time menopause occurs, using an individualized dose and duration.
This means the results should not be read as evidence that a 70-year-old woman should start estrogen to prevent Alzheimer’s disease. Starting hormone therapy later in life may have different effects on the heart, blood vessels, blood clots, cancer risk, and other health outcomes. The balance of risks and benefits must be considered for each patient.
The study also examined estrogen alone, so the findings cannot automatically be applied to combined estrogen and progestogen therapy. Previous research has raised different questions about combined treatment and dementia. The type of hormone, dose, route of delivery, timing, and duration may all matter.
The most useful interpretation is that the findings provide another reason to investigate how estrogen interacts with the aging brain. The association with lower dementia odds and less Alzheimer’s pathology is strong enough to deserve further study, particularly with modern treatment patterns. Future research could help determine whether there is a particular period in life when estrogen has different effects on brain health.
For now, the study is an interesting piece of the Alzheimer’s puzzle rather than a new prevention strategy. It suggests a possible relationship between later-life estrogen exposure and healthier brain outcomes, but it cannot prove protection.
Women should not start, stop, or change hormone therapy because of these findings without discussing their individual medical situation with a healthcare professional.
If you care about brain health, please read studies that eating apples and tea could keep dementia at bay, and Olive oil: a daily dose for better brain health.
For more health information, please see recent studies what you eat together may affect your dementia risk, and time-restricted eating: a simple way to fight aging and cancer.
Source: Stanford Medicine.
