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In women's reproductive years, their brains are exposed to high levels of sex hormones, and their neurons may come to depend on those hormones to function optimally. But leading up to and after menopause, the ovaries produce far less estrogen and progesterone, raising concerns that this drop in hormones may contribute to women's dementia risk."We think that the loss of those hormones at menopause renders those neurons more vulnerable to age-related cellular decline and pathologies like Alzheimer's," said Karyn Frick, a neuroscientist and professor of psychological and brain sciences at the University of Wisconsin-Milwaukee.So, if falling hormone levels are a risk factor for dementia, could replacing those hormones help stave off the disease?While the idea sounds logical on its face, studies that have looked at hormone replacement therapy (HRT) for dementia prevention have had mixed results. There are early hints that restoring estrogen during early menopause may protect brain health, but ultimately, more gold-standard clinical trials are needed to know for sure, experts told Live Science.Support for estrogen protecting the brainThe idea that estrogen could help ward off dementia is plausible. Women are more likely to develop Alzheimer's disease than men are, and scientists think the loss of estrogen during menopause may be partly to blame, said Jennifer Bruno, an instructor of psychiatry and behavioral sciences at Stanford University.Lab and animal studies buttress the idea that estrogen could protect brain health.In the brain, estrogens act as neuromodulators, or chemical messengers that alter how neurons behave. Estrogen also helps neurons keep their shape. Estrogen loss in female mice triggers a drop in the number of dendritic spines ‪—‬ the small, bud-like bumps on neurons that receive chemical messages.An estrogen molecule. The body's levels of estrogen fluctuate in perimenopause, and they then dramatically decline and level off during and after menopause. (Image credit: theasis via Getty Images)Researchers think that estrogen may help prevent the formation of the abnormal proteins — including one called amyloid beta — that accumulate, disrupt communication between neurons and ultimately kill cells in Alzheimer's disease. Amyloid beta is produced when a larger protein is cut the "wrong" way by an enzyme, Frick explained. Estrogen promotes the "normal" cutting of this protein, thus reducing amyloid beta, studies in lab mice show. And estrogen may limit the buildup of a second Alzheimer's-related protein, called tau, by preventing the chemical processes that cause the tau proteins to clump together. This helps prevent the formation of tau tangles, a hallmark of Alzheimer's disease.The hormone may also support brain health indirectly by improving sleep quality. "It's well documented that menopausal women have difficulty sleeping, whether it's due to hot flashes or insomnia," Frick said. Estrogen can ease those nighttime hot flashes, thus helping menopausal women get more, less-fragmented sleep. Deep rest may help the brain clean out toxic proteins, while research shows sleep deficiency is linked to Alzheimer's disease.Mixed results with estrogen-only HRTHRT for menopause comes in two main forms: treatments that include only estrogen, and combined therapies with both estrogen and progesterone. The treatment has a complicated history. HRT was popular in the 1990s but fell out of favor after results from the Women's Health Initiative study were published in 2002. That study identified various risks tied to both estrogen-only and combined HRT options, some of which have since been overturned by newer data.That said, the Women's Health Initiative study found that estrogen-only HRT came with an increased risk of endometrial cancers, and later analyses have backed up this idea. That's why today, clinical guidelines recommend that women who have not gotten a hysterectomy take combined HRT, while estrogen-only options are reserved for those who have had their uterus removed. (The added progesterone counteracts estrogen's thickening effect on the uterine lining.)For the subset of women who take estrogen-only HRT, observational data published in August showed that this form of the treatment was linked to a reduced risk of dementia. The study, published in the journal Neurology, found that women who took estrogen-only HRT were less likely to show Alzheimer's-related changes in the brain than women who didn't take any HRT.Laboratory data suggest that estrogen may help prevent the formation and accumulation of abnormal proteins that are related to Alzheimer's. (Image credit: KATERYNA KON/SCIENCE PHOTO LIBRARY via Getty Images)Estrogen-only HRT was also tied to better clinical outcomes: Treated women were less likely to be diagnosed with dementia, were less likely to show clinical and functional cognitive decline, and had better scores on memory tests, on average, compared with untreated women. These findings drew on two large, separate groups of older women, reporting data from 21,400 people in total, but they didn't include data on when each woman started HRT. Whereas earlier studies of HRT and dementia risk relied on doctors' ratings of patients' symptoms, the Neurology study measured levels of Alzheimer's-related proteins in the brain after death. That's a more "definitive" marker of disease, said Bruno, a co-author of the study. However, the research was observational, so it can't say whether estrogen-only HRT directly causes the better brain outcomes the team observed, she stressed.Although the Neurology study's findings are promising, they don't necessarily match the results of other studies of estrogen-only HRT and dementia. For example, a slightly larger observational study, published in 2023, found that estrogen-only HRT was associated with an increased dementia rate. In that research, most of the women took a type of estrogen called estradiol, while Bruno's study included a greater variety of estrogens. That may have been the difference in the two studies' results, but teasing that out would require further study. Meanwhile, the conflicting findings muddy the waters of what estrogen-only HRT can do for brain health.Does timing matter?One big finding from the Women's Health Initiative study was that starting HRT — either estrogen-only or combined — after age 65 was associated with worse cognitive function and increased dementia risk, said Yuko Hara, director of aging and Alzheimer's prevention at the Alzheimer's Drug Discovery Foundation.The same may not be true for people who start HRT earlier. For context, menopause starts around age 51 to 52, on average, and it's preceded by perimenopause, a transitional period when hormone levels begin to drop, typically around the mid-40s.An observational study published in August in the journal Alzheimer's & Dementia found that starting HRT between ages 46 and 56 was linked to a reduced risk of dementia. That study did not differentiate between estrogen-only and combined treatment; it lumped all of the data together.Patches (pictured) are one form of systemic HRT. They deliver hormones through the skin and into the bloodstream. (Image credit: SVPhilon via Getty Images)The protective link was especially strong in three groups: women with "surgical menopause," triggered by the removal of one or both ovaries; carriers of a certain variant of a gene called APOE that raises Alzheimer's risk; and women who had a relatively short time between their first period and menopause. A 2024 meta-analysis of randomized controlled trials also found that HRT had a cognitive benefit for women with surgical menopause; that finding was tied mostly to estrogen-only therapies. However, outside of that specific group, the idea of early HRT protecting brain health is far from settled.Who might benefit, if anyone?Related storiesCould we prevent dementia? A new trial may point the way.As cervical cancer rates fall, HPV is causing more throat and mouth cancers in men — why?Military's testosterone screening program could lead to overtreatment and side effects, including impaired T productionWhen it comes to using hormone replacement to protect brain health, the evidence isn't yet strong enough to recommend any kind of HRT as a way to protect the brain in all women, Hara said. Women who had one or both of their ovaries surgically removed are the exception to this rule."This is a distinct clinical population because the procedure can cause an abrupt, early loss of estrogen, rather than the gradual hormonal decline that occurs with natural menopause," Hara said. For most women who have gone through natural menopause, "there is not enough evidence to recommend [HRT] specifically for preventing cognitive decline or dementia," she said.HRT is not currently prescribed to prevent dementia — it is prescribed to ease menopause symptoms, such as hot flashes, night sweats and sleep disturbances. To settle the science on HRT and the brain, what's really needed is a well-designed clinical trial that follows women from perimenopause to postmenopause, Bruno said. That would reveal the effects of HRT on brain health and dementia risk more reliably than the studies done so far.This article is for informational purposes only and is not meant to offer medical advice.Help us improve Live Science Pro: We're always trying to make our content better. Leave us feedback about Pro here.

This brass head depicts an "oba," or ruler of the Kingdom of Benin. (Image credit: Cleveland Museum of Art (Public Domain))Quick factsName: Ancestral commemorative headWhat it is: A copper-alloy sculpture of an African ruler's headWhere it is from: Edo, NigeriaWhen it was made: Mid-1500sIn the Kingdom of Benin, one of the oldest monarchies in West Africa, a traditional ruler known as an oba would commission a brass or bronze bust of their predecessor upon taking the throne. The bust of the past oba would then be set on an ancestral altar in the palace. But when the British Empire annexed the Kingdom of Benin into colonial Nigeria in 1897, the British looted thousands of African artifacts spanning the kingdom's seven-century history, and the country of Nigeria has asked that they be returned.This particular bust is in the collection of the Cleveland Museum of Art (CMA), which acquired it from prominent French art dealer Louis Carré, who sold many of the artifacts looted from Benin to Western museums in the 1930s. This head of an oba ancestor, also known as "uhunmwun-elao" in the Edo language spoken in the historic Kingdom of Benin, is roughly 1 foot (30 centimeters) tall and was made from a copper alloy, using a lost-wax casting process that would produce one unique bust, then-CMA curator William Milliken wrote in a 1937 study.Initially, CMA experts thought the ancestral head represented a princess, due to the layers of coral necklaces around the oba's neck and the thin braids hanging from the individual's temples. But the coral necklaces and the lattice-pattern beaded caps were actually potent representations of a ruler's power. The top of the bust is partly open, and it would have supported an intricately carved elephant tusk that recorded the oba's accomplishments and major life events.Many of the surviving ancestral commemorative heads were created in the 15th and 16th centuries by the Igun Eronmwon, a hereditary guild of brass and bronze artisans that made objects for royalty in the Kingdom of Benin. According to the CMA, Benin royalty prized brass because it does not corrode. Much of the African brass was imported from as far away as Germany. When British forces invaded the Benin royal palace in 1897, they looted thousands of metal plaques, sculptures of humans and animal figures, and royal and personal ornaments that have come to be known as the Benin Bronzes, even though most of the objects are technically brass, an alloy of copper and zinc. The British Museum holds the world's largest collection of Benin brass artifacts — over 900 objects — which Nigeria formally requested be returned in 2021. Some institutions have begun repatriating this historic royal art back to its homeland. A group of German museums that collectively held over 1,100 of these objects transferred ownership of them to Nigeria in 2022. That same year, the Smithsonian's National Museum of African Art transferred ownership of 29 Benin Bronzes to Nigeria. And, in 2025, the Netherlands returned 119 Benin Bronzes to Nigeria. To date, however, the British Museum has not officially returned any of the Benin Bronzes in its collection. There is also controversy about who should have ownership of these artifacts. In 2025, the Museum of Fine Arts, Boston returned two Benin Bronzes to Oba Ewuare II, the great-great-grandson of the last oba before the 1897 British invasion. Oba Ewuare II is the Oba of Benin and custodian of Benin culture.A full catalog of royal artifacts looted from Benin in the late 19th century can be found on the Digital Benin project website.For more stunning archaeological discoveries, check out our Astonishing Artifacts archives. Kerch Crown Lady K'abel Stela Fire Flame Vessel Can you put together last week's Astonishing Artifact?

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