Women with longer periods of fertility have higher risk of dementia, says study

Portrait of young pregnant woman standing by the window
Women who have longer reproductive periods are at increased risk for dementia later in life, according to a September 2020 study. (Photo: Getty Images)

Women who have longer periods of fertility have a higher risk of dementia late in life, according to a new study.

For the study, published in the journal Alzheimer’s and Dementia, researchers looked at more than 1,300 women in Sweden from 1968 to 2012. They calculated the participants’ fertile years by tracking “the time from menarche — age at first menstruation — to age at menopause, [or] one year without menstruation,” study co-author Jenna Najar tells Yahoo Life. Najar is a doctoral student at the University of Gothenburg’s Sahlgrenska Academy and AgeCap, the Center for Aging and Health, in Sweden.

Among women with a longer period of being fertile — namely, 38 years or more — 24 percent of them developed dementia after the age of 85, compared with 16 percent of women with a shorter reproductive period of 32.6 years or less, according to EurekAlert.

Surprisingly, the number of pregnancies — which are marked by major hormonal fluctuations — wasn’t a factor in this study. Najar tells Yahoo Life that she was surprised by this particular result. “Also because other studies have found a relation between the number of pregnancies and the risk of dementia,” she says. “We were included in another study where we found that women having five or more children had an increased risk of dementia compared to women having one to four children. One reason why we did not find any association in the present study could be due to the sample size — i.e., a larger sample size might have been needed to find any true association.”

In the press release, Najar said that the study results “may explain why women have a higher risk of developing dementia and Alzheimer’s disease than men after age 85, and provide further support for the hypothesis that estrogen affects the risk of dementia among women.”

This research is one of several ways scientists are trying to understand why almost two-thirds of Americans with Alzheimer’s are women, according to the Alzheimer’s Association.

Rebecca Edelmayer, the director of scientific engagement at the Alzheimer’s Association, tells Yahoo Life that “women really are at the epicenter of Alzheimer’s disease,” and that researchers need to continue to “unravel” what contributes to their risk “both biologically and socially.”

She adds that “a lot of the research is still in its early stages. At this time, there isn’t a consensus on what is truly driving the risk in women. It’s really important that we understand these sex differences.”

But Dr. Rawan Tarawneh, an assistant professor of neurology at the Ohio State University College of Medicine, wrote in a blog post about how estrogen may play an important role: “While estrogen protects the brain from Alzheimer’s changes in younger women, this benefit is lost in older women after menopause when estrogen levels drop. Other factors include lifestyle differences between men and women, such as higher rates of depression, and a different response to stress or sleep disturbance in women compared to men.”

This new study isn’t the first to explore the relationship between menopause and dementia. A three-year brain imaging study that ended in 2018 looked at 59 adults, including premenopausal, perimenopausal and postmenopausal women, between the ages of 40 and 60. The researchers found that women in the menopausal and perimenopausal groups showed declines in an “estrogen-dependent memory test as compared to men,” according to the Cure Alzheimer’s Fund, which supported the research.

The study also found that the menopausal group showed the “highest rate of loss in an area of the brain critical for memory known as the hippocampus,” according to the Cure Alzheimer’s Fund, along with higher rates of beta-amyloid deposits — a “sticky” protein fragment that “accumulates in the brain, disrupting communication between brain cells and eventually killing them,” according to the Alzheimer’s Association.

More research is needed to understand the complicated role of estrogen in dementia risk. “However, some basic research studies have reported that estrogen [may] act toxic [to] neurons when Alzheimer’s disease pathology is present,” Najar tells Yahoo Life. “Therefore, our hypothesis is that the effect of estrogen has a negative effect on neurons in older people where dementia and Alzheimer’s disease pathology has started to accumulate.”

Najar adds: “Results from our study could explain why women have an increased risk of dementia compared to men at older ages, and these results could contribute with more knowledge on how to identify people at increased risk of dementia and Alzheimer’s disease.”

Edelmayer says studies like these that seek to understand the role of biological differences — not only between the sexes but also across racial and ethnic populations — in dementia risk are important. “It will help with developing specific diagnostic tools and prevention strategies and drive a more patient-centered approach,” she says.

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