The brain is packed with estrogen receptors. That means that when estrogen is circulating in our blood, some of it is binding to those receptors and having effects on how our brain cells function. In some cases, we know exactly what the effects of estrogen are. In many more cases, we have only some sense that estrogen is playing a role, but we don’t know exactly what it is doing or why.

Throughout women’s lives, their estrogen levels rise and fall—both in the short term during the menstrual cycle, and longer term as girls and women move from puberty to the reproductive years, including pregnancy and breastfeeding, then on to perimenopause and menopause. Those rises and falls have effects on how we perceive the world, our moods, executive function and cognition. Much of what we know about the role of estrogen in women’s bodies is based on observations of what happens when we don’t have estrogen, both after pregnancy and in perimenopause.

During pregnancy, estrogen levels are higher than any other time. With delivery, estrogen levels plummet. Many physical changes accompany that drop, and women are very susceptible to changes in mood at that time when estrogen drops. Baby blues and postpartum depression are likely triggered by dropping estrogen levels. Some women experience mood changes each month before their menstrual period, when estrogen levels are dropping. There is a growing awareness that women with attention deficit hyperactivity disorder experience more symptoms at times in their menstrual cycle when estrogen levels are low. And irritability, depression, and anxiety are common symptoms of perimenopause. Again, symptoms crop up when estrogen levels drop.

Researchers theorize that estrogen affects dopamine activity in our brain (1). When estrogen levels are high, dopamine becomes more effective. When estrogen levels drop, dopamine may be less effective. This modulation of chemicals that affect the brain may explain why low estrogen levels are associated with mood changes.

During perimenopause, women often complain of brain fog and memory changes. The Study of Women’s Health Across the Nation (SWAN) is a large, multicenter longitudinal study that has been following participants for more than 20 years (2). They found that about 60% of women note cognitive changes during the perimenopausal transition. For a long time, these symptoms were attributed to poor sleep, another common complaint among midlife women. Essentially, night sweats disrupt sleep, and poor sleep is known to affect cognitive function. But it turns out this is only part of the story.

Some participants in SWAN performed a series of cognitive tests during each of their study visits. Those tests showed that women in perimenopause experienced a decrease in memory and the speed at which they could perform mental tasks, something we call processing speed.

However, researchers did not find an association between the severity or frequency with which the women were experiencing hot flushes and night sweats, or the degree of sleep disruption, and their performance on cognitive tests. This suggests that something else is acting in the brain. Given what we do know about estrogen in the brain, it makes sense that low estrogen levels may be the culprit.

The good news is that the cognitive changes associated with perimenopause are not early signs of dementia. In fact, after the perimenopausal transition is complete measures of cognitive function rebound. In perimenopause, estrogen levels can be volatile and unpredictable. Within a few years of a woman’s last menstrual period, estrogen levels stabilize—but they remain low. The data suggests that the brain can acclimate to these new low estrogen levels.

If the cognitive symptoms associated with perimenopause are not early signs of dementia, how are estrogen and dementia connected? We don’t know for sure. But estrogen has been shown to play a critical role in regulating metabolism in our brains at a cellular level. We think the drop in estrogen seen at menopause decreases our brain’s metabolism, leading to poor function and breakdown of brain cells. Given enough time, the breakdown of brain cells may lead to dementia (3).

Ultimately, there is still a lot of work to do to fully understand the role estrogen plays in women’s brains, and how the permanent drop in estrogen at menopause may lead to dementia is some women. That critical research could lead to breakthroughs in preventing and treating dementia.