A groundbreaking study published in Neurology, the medical journal of the American Academy of Neurology, has revealed a significant association between women using hormone therapy later in life and a reduced risk of developing dementia.

The study, led by Jennifer Bruno, PhD, of Stanford Medicine in Stanford, California, analyzed medical information from two large data sets that included 21,462 female participants who underwent clinical testing while they were alive. In one data set, 728 participants received brain scans or biomarker testing during life, while in the other, 2,959 participants underwent autopsies after death, at an average age of 82, allowing researchers to examine the presence of Alzheimer’s disease in their brains.

Among all participants, 1,953 used hormone therapy, and 19,509 did not. Notably, the women who received hormone therapy began using it after age 70, which is different from the current standard practice of starting hormone therapy in the late 40s to early 50s and stopping treatment before age 60.

The analysis focused solely on estrogen-only therapy, as earlier studies had suggested that treatment combining estrogen with progestin may raise dementia risk. Under current medical practice, estrogen-only therapy is prescribed only to people who have undergone a hysterectomy due to the risk of endometrial cancer.

The researchers evaluated three major features associated with Alzheimer’s disease: amyloid-beta plaques, tau tangles, and neuritic plaques, which are amyloid plaques surrounded by damaged nerve cells. These findings were combined into a single score used to assess the amount of Alzheimer’s-related pathology in the brain.

Among women who had used hormone therapy, 18% showed no signs of Alzheimer’s disease at autopsy, compared to 10% of women who had not used the therapy. Conversely, 40% of hormone therapy users showed all three signs of Alzheimer’s disease, whereas 51% of women who had not used hormone therapy displayed the same signs.

After accounting for factors such as age, education, genetics, race, and hypertension, hormone therapy use was associated with a 35% lower odds of showing signs of Alzheimer’s disease at autopsy. Furthermore, biomarker tests collected while participants were alive revealed that women who had used hormone therapy had amyloid biomarker levels in their blood and spinal fluid consistent with less amyloid accumulating in the brain than women who did not use hormone therapy.

The study’s findings suggest that estrogen-only hormone therapy may have a protective effect against Alzheimer’s disease, particularly when used later in life. However, researchers emphasized that the results show an association and do not demonstrate that hormone therapy can prevent dementia.

While the study’s limitations, such as the different timing and type of hormone therapy use compared to current practice, are acknowledged, the findings provide valuable insights into the relationship between hormone therapy and dementia risk. Further research is needed to confirm these results and to explore the potential benefits and risks of hormone therapy in relation to brain health.