Are women at higher risk of Alzheimer鈥檚 disease?
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Nearly two-thirds of Americans with Alzheimer鈥檚 disease are women, and now some scientists are questioning the long-held assumption that it鈥檚 just because they tend to live longer than men.
What else may put woman at extra risk? Could it be genetics? Biological differences in how women age? Maybe even lifestyle factors?
Finding out might affect treatments or preventive care.
One worrisome hint is that research shows a notorious Alzheimer鈥檚-related gene has a bigger impact on women than men.
鈥淭here are enough biological questions pointing to increased risk in women that we need to delve into that and find out why,鈥 said Maria Carrillo, chief science officer for the Alzheimer鈥檚 Association.
Last month, the association brought 15 leading scientists together to ask what鈥檚 known about women鈥檚 risk. Later this summer, Carrillo said it plans to begin funding research to address some of the gaps.
鈥淭here is a lot that is not understood and not known. It鈥檚 time we did something about it,鈥 she added.
A recent Alzheimer鈥檚 Association report estimates that at age 65, women have about a one in six chance of developing Alzheimer鈥檚 during the rest of their lives, compared with a 1 in 11 chance for men.
The tricky part is determining how much of the disparity is due to women鈥檚 longevity or other factors.
鈥淚t is true that age is the greatest risk factor for developing Alzheimer鈥檚 disease,鈥 said University of Southern California professor Roberta Diaz Brinton, who presented data on gender differences at a meeting of the National Institutes of Health this year.
But, she said, 鈥渙n average, women live four or five years longer than men, and we know that Alzheimer鈥檚 is a disease that starts 20 years before the diagnosis.鈥
That鈥檚 how early cellular damage can quietly begin.
Brinton researches if menopause can be a tipping point that leaves certain women vulnerable.
However it starts brewing, there鈥檚 some evidence that once Alzheimer鈥檚 is diagnosed, women may worsen faster; scans show more rapid shrinkage of certain brain areas.
But gene research offers the most startling evidence of a sex difference.
Stanford University researchers analyzed records of more than 8,000 people for a form of a gene named ApoE-4, long known to increase Alzheimer鈥檚 risk.
Women who carry a copy of that gene variant were about twice as likely to eventually develop Alzheimer鈥檚 as women without the gene, while men鈥檚 risk was only slightly increased, Stanford鈥檚 Dr Michael Greicius reported last year.
It鈥檚 not clear why. It may be in how the gene interacts with estrogen, Brinton said.
Amy Shives, 57, of Spokane, Washington state, recalls when her mother began showing symptoms of Alzheimer鈥檚. But it wasn鈥檛 until after her own diagnosis a few years ago that Shives looked up the gender statistics.
鈥淭hat was alarming,鈥 said Shives, who is in the early stages of Alzheimer鈥檚, which struck at a younger-than-usual age and forced her retirement as a college counselor.
鈥淭he impact on our lives and that of our families is extraordinary.鈥
She points to another disproportionate burden: About 60 percent of caregivers for Alzheimer鈥檚 patients are women.
鈥淢y daughters are in their 20s and I鈥檓 already ill,鈥 Shives worries. 鈥淚t鈥檚 very stressful for them to think about when their mother鈥檚 going to need their help.鈥
What drives the difference in Alzheimer鈥檚 cases isn鈥檛 clear, said Dr Susan Resnick of the National Institutes of Health, pointing to conflicting research.
鈥淲e really have had a tough time understanding whether or not women really are more affected by the disease, or it鈥檚 just that they live longer,鈥 Resnick said.
Data from the long-running Framingham, Massachusetts, health study suggests that because more men die from heart disease in middle age, those who survive past 65 may have healthier hearts that in turn provide some brain protection.
Many of the same factors 鈥 obesity, high cholesterol, diabetes 鈥 that damage arteries also are Alzheimer鈥檚 risks.
What about hormones? That鈥檚 been hard to pin down. Years ago, a major study found that estrogen therapy after 65 might increase risk of dementia, although later research showed hormone replacement around the onset of menopause wasn鈥檛 a problem.
Brinton studies how menopause changes the brain. Estrogen helps regulate the brain鈥檚 metabolism, how it produces the energy for proper cognitive function, and it must switch to a less efficient backup method as estrogen plummets, she explained.
鈥淚t鈥檚 like the brain is a little bit diabetic,鈥 said Brinton, who is studying whether that may relate to menopausal symptoms in women who later experience cognitive problems.
Carrillo notes that 40 years ago, heart disease was studied mainly in men, with little understanding of how women鈥檚 heart risks can differ.
鈥淗ow do we make sure we鈥檙e not making that mistake when it comes to Alzheimer鈥檚?鈥 she asked.
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