For many years, healthcare professionals have been intrigued by the fact that women are diagnosed with Alzheimer’s disease at nearly double the rate of men.

According to estimates, approximately seven million individuals in the U.S. suffer from Alzheimer’s disease, and this number is projected to rise to nearly 13 million by 2050. Notably, around two-thirds of these cases involve women.

Emerging research indicates that estrogen, the principal female hormone, may have a significant role, particularly during the transition from perimenopause to menopause when natural hormonal levels begin to decline.

Estrogen serves various functions in the body, including enhancing cardiovascular health and sustaining bone density. Moreover, it is crucial for brain health, exhibiting neuroprotective qualities that shield brain cells from inflammation, stress, and various forms of cellular damage.

Researchers focusing on Alzheimer’s disease are turning their attention to early perimenopause, which typically occurs in a woman’s early to mid-40s, as a key period for hormone replacement therapy aimed at sustaining estrogen levels and potentially preventing dementia in certain women decades later.

“This interest stems from many years of preclinical research, animal studies, and fundamental science showing that menopause represents a critical juncture in Alzheimer’s disease,” remarked Lisa Mosconi, head of the Alzheimer’s Disease Prevention Program at Weill Cornell Medicine.

Mosconi leads a new $50 million global initiative named CARE, aimed at minimizing women’s Alzheimer’s disease risk through endocrinology research. This venture will examine biomarkers in around 100 million women, promising to be the most extensive analysis of why women face a heightened risk of Alzheimer’s disease.

The relationship between estrogen and dementia has recently attracted renewed interest following the Food and Drug Administration’s decision to lift a long-standing black box warning on hormone replacement therapy, potentially encouraging more prescriptions for women in their 40s and 50s.

Healthcare providers believe that relaxing these regulations could help destigmatize hormone therapy. The FDA’s action may also facilitate further research into whether hormone replacement therapy offers additional advantages, such as dementia prevention.

Reduction of Reproductive Hormones

Menopause is defined by a gradual decline in the production of estrogen and progesterone by the ovaries, which are essential for regulating the menstrual cycle. These sex hormones are present in women and, to a lesser extent, in men, and they play vital roles in sexual and reproductive development.

Most women experience menopause between the ages of 45 and 55, according to Dr. Monica Christmas, a gynecologist and director of the Menopause Program at the University of Chicago Medicine. The transition may commence years earlier, during perimenopause, which usually starts in a woman’s mid-40s, often accompanied by symptoms such as hot flashes, night sweats, mood swings, and sleep disruptions.

It is believed that menopausal symptoms arise from the reduced levels of estrogen and progesterone. For instance, when estrogen levels drop, the thermostat in the body, governed by the hypothalamus, fails to work correctly. The brain senses an increase in body temperature and signals sweating to cool down, leading to hot flash experiences. Hormone therapy can restore these levels, helping to regulate body temperature.

What Role Does Estrogen Play?

Rachel Buckley, an associate professor of neurology at Massachusetts General Hospital, whose research investigates gender disparities in Alzheimer’s disease, notes that receptors for this sex hormone are distributed throughout the brain.

“Estrogen is an extremely potent hormone,” she said. “It resides in a region called the hippocampus,” which is closely linked to memory and learning.

Estrogen also facilitates healthy blood flow in the brain, allowing for more efficient energy utilization, she mentioned. However, during menopause, estrogen levels begin to decrease, potentially rendering the brain more vulnerable to damage.

“When the brain loses the protective benefits of estrogen and other sex hormones, this marks a critical phase where Alzheimer’s disease can begin to accumulate in the brain,” Mosconi explains.

Can Hormone Replacement Therapy Combat Dementia?

Hormone replacement therapy is available in numerous formats, including patches, creams, and tablets, which may contain estrogen, progesterone, or both. If estrogen aids in safeguarding the brain, it stands to reason that adjusting estrogen levels through hormone therapy could offer some advantages.

Nevertheless, experts indicate that the reality is more complex, as the evidence surrounding hormone replacement therapy remains varied and ongoing.

Dr. Kellyanne Niotis, a preventive neurologist in Florida and a faculty member at Weill Cornell Medical College, noted that research suggests the perimenopausal transition is a crucial window for treatments that may help some patients prevent dementia.

“The central idea is that during the perimenopause phase, hormones fluctuate significantly, leading to rapid drops in [estrogen] which can be detrimental to brain health,” Niotis stated.

“The goal is to maintain consistent hormone levels to ease those fluctuations.”

A comprehensive analysis led by Mosconi and her team is set to be published in Frontiers in Aging Neuroscience in 2023, indicating there might be an optimal moment to commence HRT for women facing cognitive decline.

Her research evaluated over 50 studies and found that individuals undergoing estrogen therapy in midlife, within ten years following their last menstrual period, experienced a notably reduced risk of dementia.

Conversely, initiating combination hormone therapy after age 65 correlated with an increased risk of dementia.

Another large-scale review of 50 studies presented recently at the American Academy of Neurology Annual Meeting revealed that women who began HRT within five years of menopause had up to a 32% lower risk of Alzheimer’s disease compared to those receiving a placebo or no treatment. This study has yet to undergo peer review or publication in a scientific journal.

This investigation, conducted by researchers in India, also indicated that women who delayed treatment until 65 or older exhibited a 38% increased risk of Alzheimer’s disease.

However, much of the existing research is observational and does not establish a direct cause-and-effect relationship, according to Christmas. More in-depth studies, including large clinical trials, are necessary, she emphasized.

It should also be noted that prescribed hormone therapy may not function identically to the naturally produced estrogen, necessitating further investigation, she added.

Why Timing of Hormone Therapy Matters

The notion that there is a critical period for initiating hormone replacement therapy is possibly linked to estrogen receptors in the brain, according to Mosconi. Her research indicates that during the transition to menopause, the density of estrogen receptors on brain cells gradually increases, a finding supported by her studies.

This increase occurs as the brain attempts to compensate for declining estrogen levels by boosting available receptors to utilize any remaining estrogen effectively, she explained.

However, there comes a point when estrogen levels fall permanently, leading the brain to stop trying and the estrogen receptors disappear, she added.

“Once the estrogen receptors are absent, administering estrogen becomes futile as there would be nothing to bind to; that’s when the window closes,” stated Mosconi.

Numerous questions remain unanswered, such as how long women should stay on hormone replacement therapy and whether estrogen provides more protection for those with a genetic susceptibility to Alzheimer’s disease. It remains unclear how the brain responds to natural estrogen versus that received through hormone replacement therapy.

Conversely, men possess biologically different brains with significantly fewer estrogen receptors, which diminishes their need for the hormone, according to Buckley.

It is also uncertain whether testosterone replacement therapy in men might have benefits in Alzheimer’s disease prevention, as Dr. Niotis pointed out. While some research suggests a correlation between low testosterone in men and dementia, further studies are necessary before definitive assertions can be made.

Experts caution that it’s premature to advocate for hormone replacement therapy as a preventive measure for Alzheimer’s disease.

“We currently do not utilize hormone therapy for Alzheimer’s disease prevention,” remarked Mosconi. “Current clinical guidelines do not endorse hormone therapy solely for this purpose.”

Instead, HRT should be primarily prescribed to alleviate moderate to severe menopausal symptoms that impact quality of life, such as hot flashes, night sweats, sleep disturbances, and mood changes.

According to Niotis, individuals with good sleep quality tend to feel better and think more clearly, suggesting that alleviating these symptoms could enhance cognitive function.

Nonetheless, she remains hopeful that future research will yield more conclusive insights.

“The aspiration is that with the removal of the black box warning, more women will opt for treatment without reservations, and physicians will feel more confident prescribing it,” Niotis expressed.