Since about two-thirds of Americans with Alzheimer’s disease are women, experts have speculated on why women are at higher risk. Estrogen is thought to be one factor, as levels of this hormone drop after menopause. In a new study published in the journal Neurology, researchers studied the gray matter in the brains of almost 100 women. They found that menopause leads to a decline in estrogen levels, associated with lower gray matter volume in the regions of the brain vulnerable to Alzheimer’s. But, among women with higher estrogen levels, such as those who used hormone replacement or who had more children, they had greater gray matter volume in those brain regions. More research in this area is needed, but it suggests estrogen could preserve women’s brain health, countering the effects of menopause.