Women get Alzheimer’s more often than men: Five things the science tells us – Stanford Medicine

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Alzheimer’s April 01, 2026
By Sarah Williams
Women develop Alzheimer’s disease at higher rates than men. Stanford Medicine neurologists explain what science knows about why and the many things it doesn’t yet know.
Two-thirds of Americans living with Alzheimer’s disease today are women. That sobering data point has been cited by the Alzheimer’s Association and others for years but it still tends to catch people off guard.
Why would the devastating degenerative brain disease that impacts 55 million people worldwide affect women differently than men? And are there things women should be doing to protect themselves from what seems to be a greater risk?
With hormone replacement therapy making a comeback — more women are taking estrogen after menopause to offset its effects than five years ago — many are also wondering what that means for their brain.
The answers are more complicated than you might hope, according to two Stanford Medicine experts who have dedicated much of their careers to Alzheimer’s research.
“I won’t have any easy answers as we talk about this,” warned neurologist Victor Henderson, MD.
To sort through what’s known and what still needs studying, we talked to Henderson, professor of epidemiology and population health and director of the NIH Stanford Alzheimer’s Disease Research Center, as well as neurologist Michael Greicius, MD, founding director of the Stanford Memory Disorders Center.
Here are the key takeaways.
The two-thirds statistic is real, but it can be misleading. Alzheimer’s is an age-associated disease, with rates drastically increasing as people hit their 70s and 80s. Studies have shown that nearly a third of people over age 85 have some form of dementia, as do up to half of all people in their 90s.
Because women outlive men, there are simply more women in the highest-risk age groups (there are more than twice as many women over age 90 than men, for instance).
“The main difference in prevalence, the actual numbers of women who develop Alzheimer’s compared with men, is mostly due to longevity differences,” Henderson said.
Still, studies that control for age have found some differences based on sex, though not the two-to-one ratio that the raw numbers suggest.
“I think women at any given age are a little bit more likely to get Alzheimer’s than men are,” Greicius said. “But it’s probably more like three women diagnosed with Alzheimer’s for every two men.”
Other dementias tell a different story, Greicius points out. Lewy body dementia — the second most common neurodegenerative dementia after Alzheimer’s — actually skews in the opposite direction, affecting roughly twice as many men as women.
APOE4 is the strongest known genetic risk factor for late-onset Alzheimer’s, but it turns out this increased risk is steeper for women.
Greicius and Henderson, working together, were among the first to document this difference in 2014. APOE4, they found, raised dementia risk 81% in women but only 27% in men. Greicius said this may help explain part of the overall sex disparity in Alzheimer’s rates.
His team is also exploring a possible explanation for why APOE4 may convey different risk based on sex. There is a stretch of DNA near the APOE gene where the hormone estrogen can directly bind, preliminary research has suggested. That means that the presence or absence of estrogen could impact how much of the APOE protein gets produced, although he notes more studies are needed to show whether this is the case.
Greicius said he makes sure to counsel women about their increased risk when they are carriers of the APOE4 gene.
“Increasingly, I make sure to weave that into my conversation, because we have a lot of data now supporting that differential risk with APOE4 in men and women,” he said.
The presence of the estrogen binding site near the APOE4 gene isn’t the only reason to think that estrogen might be involved in Alzheimer’s. There are receptors for the hormone scattered throughout the brain, and the period around menopause — when estrogen levels in women plummet — coincides with when Alzheimer’s-associated changes in the brain are thought to begin accumulating.
“This could all be coincidental,” said Henderson, who has spent much of his career looking at the interplay between estrogen and dementia. “But there is a fair amount of observational evidence that the loss of estrogen at menopause might be associated with Alzheimer’s disease several decades later.”
So, does hormone replacement therapy, which boosts levels of estrogen, prevent dementia?
When the Women’s Health Initiative results came out in the early 2000s, early data from a sub-study suggested that certain hormone therapies could do the reverse, raising dementia risk. But more recent trials — especially those in which estrogen replacement was started earlier — have not shown the same risk.
“Unfortunately, we’re not sure about the impacts of hormone replacement right now,” Henderson said. “By and large, most clinical trials don’t show much cognitive benefit or harm either way.”
Both Henderson and Greicius say dementia risk probably shouldn’t be driving the HRT decision, even in women at heightened risk of Alzheimer’s.
“I don’t recommend menopausal hormone therapy to prevent dementia, but if a woman is already taking it for other reasons, I don’t think the dementia risk should scare her off,” Henderson said.
For most of medical research history, animal model studies were conducted predominantly in males, and early human trials weren’t much better. Female hormone cycles were seen as a variable that made results harder to interpret.
“Ninety-nine percent of mouse studies in Alzheimer’s disease were conducted in male mice only,” Greicius said. “Which seems laughable now.”
Today, more women are included in Alzheimer’s research studies, but Henderson said most studies aren’t designed to analyze results by sex, making it hard to know whether drugs have a different impact. In part, that hesitation is because if a study clearly illustrated different effects in men and women, it might complicate how the drugs are advertised or prescribed, Henderson said.
“Pharmaceutical companies are supposed to do this, but some don’t because they don’t want it to affect their marketing down the road,” he said.
After clinical trial results are published, he adds, analysis sometimes reveals small differences, such as with lecanemab, the drug recently approved by the U.S. Food and Drug Administration for mild Alzheimer’s. The published data suggested women might benefit less than men do from the drug. More research is needed to show whether that is the case, since the trial wasn’t designed to answer that question.
For now, Henderson and Greicius say they will continue to treat Alzheimer’s the same in men and women — until a time comes when well-designed trials conclude they should do otherwise.
The good news is that most of what’s known about reducing Alzheimer’s risk applies equally to women and men: exercise regularly, manage blood pressure, stay socially and cognitively engaged, get enough sleep, and don’t smoke. None of that advice changes based on sex.
But Henderson notes that because men and women tend to live differently, the same risk factors often play out differently in practice. Where people work, what they eat, how much they exercise, how much air pollution they’re exposed to — all of these vary systematically between men and women, and all have been linked to dementia risk.
“It’s not just biological differences that could explain why women may get more Alzheimer’s,” he said, “but lifestyle differences too.”
That means that the gap in Alzheimer’s rates between women and men isn’t entirely in their DNA; it’s shaped by factors that can change. Women today are more educated and health-aware than previous generations, and there’s already evidence that’s making a difference: Dementia rates have been declining in recent decades.
“The modifiable risk factors for dementia — things like blood pressure, exercise, staying socially engaged — if we can move the needle on those, we should be able to reduce the burden of Alzheimer’s,” Henderson said. “And women stand to gain from that.”
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