Women represent about 67 percent of patients with Alzheimer’s disease, a statistic that has spurred interest in the biological differences between male and female brains. The sharp decline in estrogen levels during menopause is believed to be a primary factor that makes women more vulnerable to the disease. Early research using animal models suggests that estrogen may actually help prevent the formation of beta-amyloid plaques, reduce inflammation, and protect the blood-brain barrier. Despite these promising theoretical benefits, recent studies have produced conflicting results, with some finding no effect on dementia risk, others suggesting a reduction, and a few reporting potential harm. To resolve this uncertainty, researchers from Stanford University and Johns Hopkins University analyzed data from two large studies involving over 21,460 women.
The team examined data from the National Alzheimer’s Coordinating Center, which included autopsies for nearly 3,000 women. In this group, women who took hormone replacement therapy were less likely to have tau protein tangles, beta-amyloid plaques, or neuritic plaques in their brains. The difference was significant: 18 percent of HRT users showed no signs of Alzheimer’s disease in their brains, compared to just ten percent of those who did not take the therapy. Conversely, 40 percent of HRT users had all three signs of Alzheimer’s, versus 51 percent of non-users. After adjusting for age, race, education, genetics, and hypertension, the researchers calculated that women who took estrogen-only HRT had 35 percent lower odds of showing signs of Alzheimer’s at autopsy.
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While the autopsy data showed a clear protective effect, results from the second data set were mixed. This set, which included more than 720 participants from the Alzheimer’s Disease Neuroimaging Initiative, used brain scans and fluid tests. The researchers found that hormone replacement therapy was associated with higher levels of beta-amyloid protein in the blood and spinal fluid, which corresponds to less protein being deposited as plaques in the brain. When the data from both sets was analyzed together, the researchers concluded that receiving HRT was associated with a 39 percent lower chance of being diagnosed with dementia and a reduced risk of memory problems or functional decline.
It is important to note that many of the women in the earlier data sets had started taking HRT when they were over age 70. The current medical recommendation for treating menopausal symptoms is for women to start combined estrogen-progestin HRT in their late 40s or early 50s and stop taking it before they turn 60. This timing is critical because the relationship between hormone therapy and brain health appears to depend heavily on when the treatment begins. Women should talk to their doctor to see if they are a candidate for HRT and what kind of hormone replacement may be best. Estrogen-only HRT is prescribed only for women who have had their uterus removed, while the progestin in combined estrogen-progestin HRT protects those with a uterus against uterine cancer.
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Despite these findings, the study and a related editorial published in Neurology emphasize that this type of research cannot prove that HRT has a role in lowering that risk. Randomized clinical trials and observational studies will be needed to uncover what causes may underlie this association and to help women make more informed decisions about care. The evidence suggests a potential link, but it does not yet provide a definitive answer for medical guidance.
