NOEL KING, HOST:
Alzheimer's disease affects about twice as many women as men. And now scientists are beginning to understand why. This week at the Alzheimer's Association International Conference in Los Angeles, some new research was presented, and NPR's Jon Hamilton tells us about it.
JON HAMILTON, BYLINE: One hallmark of Alzheimer's is a toxic protein called tau. And Sepideh Shokouhi of Vanderbilt University says once tau shows up in the brain, it begins to spread.
SEPIDEH SHOKOUHI: We think it goes from neuron to neuron and moves from one part of the brain to the next part.
HAMILTON: Shokouhi was part of a team that used brain scans to compare this process in more than 400 men and women. Some had mild cognitive impairment, a memory problem that often precedes Alzheimer's. And Shokouhi says in this group, a person's sex affected where tau appeared in the brain.
SHOKOUHI: We saw a more spread out pattern in women with mild cognitive impairments than men with mild cognitive impairments.
HAMILTON: Shokouhi says in women, tau appears to move more easily from one brain area to another.
SHOKOUHI: We think it affects the way that tau spreads in the brain, and we think it accelerates it.
HAMILTON: Another study looked at how work and family experience affected women's risk of memory problems in later life. Elizabeth Rose Mayeda of the University of California, Los Angeles was part of a team that studied more than 6,000 women born from 1935 to 1956. She says the team found that working outside the home is good for the brain.
ELIZABETH ROSE MAYEDA: After age 60, women who had previously participated in the paid labor force when working age experienced slower memory decline than women who had not engaged in the paid labor force.
HAMILTON: The benefit from working held whether or not women were married or had children. It also held for women who left the workforce temporarily for family reasons. The study didn't try to show why work made a difference, but Mayeda says there are lots of possibilities.
MAYEDA: Cognitive stimulation, social benefits of working, as well as financial benefits, for example, financial independence for women who engaged in the paid labor force.
HAMILTON: Poverty is a known risk factor for mental decline in later life. Heather Snyder, a scientist at the Alzheimer's Association, says in the past, researchers thought more women got Alzheimer's because they lived longer than men. She says a few years ago that thinking began to change.
HEATHER SNYDER: As we started to look at the science and what the science was showing, it did start to suggest that there were differences in the brains of women and men that may contribute to why more women are living with this disease than men.
HAMILTON: Snyder says now, lots of Alzheimer's researchers are studying sex differences.
SNYDER: There's different biology that contributes to an individual's risk - changes in hormonal systems throughout life, our immune system. Women and men have different immune systems, and that's no different in our brain.
HAMILTON: At the conference, one team reported that women's brains maintain a higher metabolism than men's as Alzheimer's develops. Another team found that the risk of Alzheimer's is influenced by different genes in men and women. Dallas Anderson, a neuroepidemiologist at the National Institute on Aging, says it's remarkable that scientists are only now beginning to understand sex differences in Alzheimer's.
DALLAS ANDERSON: Sex is such a basic variable. It's one of the key variables that we look at in population studies. And you'd think that we really would have nailed things down by now, but no.
HAMILTON: Anderson says the National Institutes of Health is working to change that by funding more studies that look for sex differences in the brain. Jon Hamilton, NPR News.
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