Stanford Study Ties Estrogen to 35% Fewer Alzheimer's Signs
A Stanford Medicine study in Neurology compared autopsies of 258 women who took estrogen with 2,701 who did not. The odds of Alzheimer's pathology were 35% lower with estrogen therapy.
A team from Stanford University published a study on August 12, 2026, in the journal Neurology linking menopausal hormone therapy based on estrogen alone to fewer Alzheimer’s deposits in the brain. The finding comes from autopsies, the material considered the gold standard for diagnosing the disease. Among women who had taken estrogen only therapy, the odds of Alzheimer’s pathology showing up at autopsy were 35% lower than among women who had never used the therapy. The paper carries the identifier 10.1212/WNL.0000000000218413.
Until now, research into the link between menopausal hormone therapy and memory has relied mostly on cognitive tests and on biomarkers drawn from blood and cerebrospinal fluid. The results have been inconsistent. Some studies pointed to a protective effect, others found no benefit at all, and still others suggested an increased risk, particularly when therapy started after age 65.
The study’s lead author is Hadi Hoseini, associate professor of psychiatry and behavioral sciences at Stanford. Lead co-authorship is shared by Jennifer Bruno and former postdoctoral researcher Jacob Shaw.
Our study is unique in that we looked at all the standards for diagnosing Alzheimer’s disease, including the gold standard outcome, which is Alzheimer’s markers in autopsied brains.
That is how Hoseini described the difference from earlier literature, in a Stanford Medicine statement. The same author also explained why blood and spinal fluid are not enough on their own.
While great progress has been made with blood and cerebrospinal fluid biomarkers, they don’t tell you how much brain damage there is or exactly where it is located.
How the study was carried out
Researchers searched two existing databases holding a combined 21,462 participants, average age around 70, all over 50. From that pool they identified the women who had donated their brains for analysis after death.
The team compared 258 autopsies of women who reported having used estrogen only therapy with roughly 2,701 autopsies of women who had never used any form of hormone therapy. The tissue was examined for three markers: amyloid deposits, tau protein tangles and the density of neuritic plaques. The results were scored, and the analysis was adjusted for age, the APOE4 genetic variant, high blood pressure, education and race.
Alongside the 35% lower odds of pathology, women on the therapy also had 39% lower odds of receiving a clinical dementia diagnosis during their lifetime. Eighteen percent of women on hormone therapy showed no signs of Alzheimer’s disease at autopsy at all, compared with 10% of those who had not taken it. Measurements taken in living participants pointed the same way: less amyloid in blood and cerebrospinal fluid, better memory test scores and less decline in the ability to live independently.
Estrogen only therapy is prescribed to women who have had a hysterectomy, since estrogen without progestin carries a higher risk of endometrial cancer in women who still have a uterus. More than 30% of women undergo that surgery by age 60, so the finding applies to roughly a third of women of menopausal age. About two thirds of people living with Alzheimer’s disease are women.
Why the earlier guidance went the other way
A major shift in clinical practice followed the 2003 analysis of the Women’s Health Initiative Memory Study, which linked combined estrogen and progestin therapy to a higher risk of dementia when started later in life, along with a higher risk of breast cancer and heart disease. The U.S. Food and Drug Administration withdrew the black box warning that grew out of that finding in 2025, but use of the therapy had already declined by then. An estimate that around 27% of women had used menopausal hormone therapy at some point in their lives is now below 5%.
Bruno described the effect with caution.
Menopausal hormone therapy appears to have a modest but meaningful and statistically significant protective effect against the risk of developing Alzheimer’s pathology.
She also addressed how the result sits against the earlier clinical guidance: “For a long time, the recommendation was that menopausal hormone therapy shouldn’t be used because it weakens memory. This study runs counter to that recommendation.”
Gayatri Devi, a neurologist at the Zucker School of Medicine at Hofstra and Northwell Health in New York who was not involved in the research, told Science News that the paper fills in part of the picture: “This study adds an important piece to the growing body of evidence on menopausal hormone therapy and brain health.”
What the study does not prove
The study shows an association, not causation. It is an analysis of existing databases, not a clinical trial with randomized assignment of therapy, so it cannot be used to conclude that estrogen prevents Alzheimer’s disease.
The limitations run narrower than they might first appear. The finding applies only to estrogen alone, not to the combination with progestin, because the number of autopsies of women on that combination was too small to draw a conclusion. It also applies only to oral use, since women using local estrogen preparations were not included in the analysis. The women in the sample were older and had started therapy long ago, often decades earlier, when both the formulations available and the timing of starting therapy differed from current practice.
The research was funded by the U.S. National Institutes of Health (NIH) through seven grants. The authors are calling for the next step to be clinical trials that track biomarkers and memory from the start of menopause, with a separate analysis of combined therapy. Bruno also told Science News who that task falls to: “Women can advocate for future studies that would really clarify the causality of this.”
