Women make up two-thirds of the people living with Alzheimer’s disease. Given the general population is about half women, that means women are disproportionately affected. Why? For a long time, researchers attributed the disparity to the fact that women live longer than men on average, and since Alzheimer’s becomes more frequent in older men and women, it seemed to make sense that it would affect more women. However, living longer isn’t the only risk factor for developing Alzheimer’s. According to a report published by the Alzheimer’s Association titled Alzheimer’s Disease Facts and Figures, of all Americans who are 71 and older, 16 percent of all women have Alzheimer’s disease and other forms of dementia, and only 11 percent of men have some form of dementia.
Many studies have been done about what makes women more susceptible to Alzheimer’s disease. We will briefly touch on a few studies related to gender differences in Alzheimer’s risk. One study, the Alzheimer’s Disease Neuroimaging Initiative, looked at how cognitive abilities of study participants with mild cognitive impairment changed over the course of their study (about 8 years). They found that women with cognitive impairment decline at a rate that’s almost twice as fast as men who had similar impairment at the beginning of the study.
There are also studies that show women tend to accumulate more amyloid beta in their brains than men to, and beta-amyloid build up is one of the main factors in the development of Alzheimer’s disease.
The big question is, why does this happen? Why are women apparently more susceptible to developing Alzheimer’s disease than men? Some researchers believe it’s because women’s cells all carry two X chromosomes, and men’s cells carry one X and one Y, and the two X chromosomes could be putting women at higher risk. A study done at Mayo Clinic and published in Nature Genetics in 2009, titled Variants in Gene on X Chromosome Associated with Increased Susceptibility to Alzheimer’s, found that having two copies of a variant in the PCDH11X gene, which is found only on the X chromosome, put women at a much higher risk of developing Alzheimer’s disease. Women and men who only had one affected X chromosome also had an increased risk.
According to Steven Younki, senior investigator of the study, the PCDH11X variant is a common genetic variant, and not everyone in the study who had the variant – even women with a variant in each X chromosome – had Alzheimer’s disease at the time of the study. But there were significantly higher odds that study participants with Alzheimer’s disease were female patients with two copies of the genetic variant.
Other researchers believe women have a higher risk because of the effects of menopause. A professor at the School of Pharmacy at the University of Southern California, Roberta Diaz Brinton, says her research shows that women are at higher risk because of the role estrogen plays in regulating energy supply to the brain. She says the changes women’s bodies undergo during menopause can alter the brain’s ability to convert glucose into energy. And at least one recent study has shown that lower brain metabolism is present in those who develop Alzheimer’s disease – even before other signs and symptoms appear.
Using data from the Oregon Brain Aging Study and the Intelligent Systems for Assessing Aging Changes project, researchers at the Oregon Health & Science University in Portland looked at people who experienced cognitive decline after having surgery with general anesthesia. They found that the combination of surgery and anesthesia may speed up cognitive decline in elderly people – and elderly women decline faster than elderly men. The same study showed that women with more surgeries and anesthesia declined faster.
While it’s still not clear why women are more susceptible to Alzheimer’s than men, there is plenty of evidence that they are, and many studies are now focusing on gender differences in Alzheimer’s disease and other forms of dementia. Hopefully, with time, researchers will uncover the mysteries behind Alzheimer’s that may lead to successful treatments and even a cure.
To learn more, feel free to check out our recent blogs on how to care for a parent with Alzheimer’s or another form of dementia at home and how to communicate with a loved one who has dementia.