Does estrogen protect against dementia? And if so, who should take it?

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.

The 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.

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 .