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Hormone fluctuations and effects on sleep may contribute to memory disorders in women, UCI researcher says

Hormone fluctuations and effects on sleep may contribute to memory disorders in women, UCI researcher says
Sara Mednick, a UC Irvine associate professor of psychology, is studying the effects of menstruation on sleep. She said the waxing and waning of sex hormones could be increasing women’s risk of memory-related diseases like Alzheimer’s. (Heather Ashbach / UC Irvine)

About two-thirds of people living with Alzheimer’s disease are women.

The Alzheimer’s Assn. reports there are “a number of biological and social reasons” that women are more likely than men to develop Alzheimer’s and other forms of dementia.

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Life expectancy is one of them.

But some studies, the organization said, indicate that the likelihood of developing a memory-related disorder may stem from biological and genetic variations or the life experiences of women.

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Sara Mednick, an associate professor of psychology at UC Irvine, said her research suggests that menstrual cycles and their effects on sleep might have something to do with it.

In a study published in November 2017, Mednick and her team tested the memories of men and women before they took a nap. Women were tested twice at different points in their menstrual cycles, when hormonal changes prepare the body for the possibility of pregnancy.

The subjects were monitored for their brain activity, blood oxygen levels, heart rate, breathing and any eye or leg movements that occurred in their sleep.

After waking up, the subjects were tested again.

“We gave people memory tests to see how much they forget across a period of sleep. Usually what you’d find is sleep is better for consolidating your memory,” Mednick said. “But what we found is … women during their menses … were really unable to benefit from sleep as compared to when that woman is in her non-menses period.

“[The study] showed women in general had better memories than men when it came to face-name recognition. But when we looked at their memory across sleep, women during their menses were not able to use sleep to benefit their performance.”

Mednick said that’s likely because of fluctuations of the sleep spindles — sudden bursts in brain wave activity that occur in the second stage of “light” sleep that are important to memory consolidation. But as the spindles fluctuate in the course of a menstrual cycle, long-term memory may be affected, contributing to the development of memory-related illnesses as women age.

Kate Simon, a postdoctoral researcher working with Mednick at UCI’s Sleep and Cognition Lab, said they are doing a new study looking at women at different points of the standard menstrual cycle — young women, perimenopausal and menopausal.

The researchers will observe the subjects four different times in their cycles to see whether they can observe where women are having the most trouble consolidating their memories.

Mednick and her team also will be observing men to compare data between men and women.

The study is funded by a five-year, $1.8-million grant from the National Institute of Aging.

“The most impactful scientific insights result from studies that consider the whole of human diversity,” said Bill Maurer, dean of UC Irvine’s School of Social Sciences. “Professor Mednick’s groundbreaking research reminds us that you can’t just draw scientific conclusions by focusing on men alone, like so much biomedical research does.”

Simon said “we are not in a place where we can understand the biological differences between men and women. It’s an area of research that’s just opening up that looks at how our hormones might affect our cognitive processes and, if they do, what’s important is how and why so we can create intensive treatments and understand what’s going on.”

The study focuses not just on brain activity but on the entire body and “how everything is working together,” she said.

The goal is to see whether sleep intervention can be done to identify where in the cycle women are having the most difficulty with consolidation of their long-term memories and, hopefully, Mednick said, whether intervention can increase sleep spindles to compensate for the waxing and waning during that time.

“Knowledge is power,” Mednick said. “If we can predict why any disease happens, we are in a much stronger position to prepare for it and potentially stop it.”

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