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Key points
- Two thirds of the people who suffer with dementia, including Alzheimer's Disease, are women.
- Part of this is the consequence of longevity, women live longer than men.
- But there may be other reasons, our hormones for a start.
Much of what piques my fear that I will develop the same illness that stole my mother (though develop seems to be the wrong word—this is the coming undone of cognition, of a life, after all), is the fact I share her gender.
Women are twice as likely as men to succumb to dementia. Nearly two-thirds of the 5 million Americans living with Alzheimer's are women. Is this because we live longer, and in our dotage is a window of sinister opportunity flung open to create a crack for this disease to slink through? Is it hormone-related? Is it because our neuro-protective oestrogen dries up at menopause so our brains begin to dry up, too? Or is it because our testosterone levels are far lower than in men?
I asked Christopher R. Beam, Ph.D., assistant professor of psychology and gerontology at the University of Southern California what he thinks. He published a study that showed that the incidence of dementia and Alzheimer's disease— the number of new cases of these at different ages in the lifespan—“were about the same in men as women until the mid-80s. Around 85 or so, rates of any type of dementia (Alzheimer's disease, vascular dementia, Lewy body dementia) begin to decline faster in men than women. For Alzheimer's disease, which constitutes close to 75 percent of dementia cases, incidence rates in women diverge earlier in the lifespan.”
We don't really know why almost 66 percent of all Alzheimer's disease cases in the United States are women, he says, "But because age is the greatest risk factor of Alzheimer's disease and women live longer than men, on average, longevity is one of the leading hypotheses as to why women are diagnosed with Alzheimer's disease more often than men.”
Age Is Not the Only Factor
Certainly, according to the Alzheimer’s Association, this has been the long-held view but “emerging evidence suggests it may not be the whole story.”
Says Beam, “We have looked into whether genetic variance underlying Alzheimer's disease differs between men and women.” Early research suggested that the APOE e4 genotype, which is the one responsible for dementia, was more prevalent in women with Alzheimer's disease than men. But Beam’s team found that genetic variance was the same in women as men. Another hypothesis that has been put forward as to the differential between the prevalence in women versus men, he continues, “Is that differences in sex hormones explain women's greater likelihood of AD diagnosis. We don't know yet whether oestrogen replacement therapy prevents AD onset, but in one of our twin studies of same-sex and opposite-sex fraternal twins, we found that female twins with a male co-twin were less likely to be diagnosed with dementia than female twins with a female co-twin." The idea was to test whether testosterone transfer in utero conferred a protective benefit to female twins from eventually being diagnosed with Alzheimer's. He continues, "The results were heartening because the effect of having a male co-twin for female twins held even after taking into account post-natal hormone exposure.”
Scientists continue to study the male-female disparity from varying angles; genetic contributions, brain structure, how cells use and metabolize energy, immune system and cardiovascular system differences, life-course hormonal changes, and other biological or social factors.
Because it may indeed be hormone-related, says Amy Johnston, associate director of media engagement at the Alzheimer’s Association, one area researchers are exploring is the female reproductive cycle. Some studies have found a link between the risk of dementia, age at first menstruation, age at menopause, and time between the two. This research, she says, “Suggests that a longer reproductive period across a life course may decrease one's risk for dementia.”
Sex-Specific Differences in the Brain
Researchers are also investigating sex-specific differences in the architecture of the brain. Scientists have found that differences in the structural and functional connections of a woman's brain may speed the spread of tau, the protein that clumps into the tell-tale tangles of dementia and which may contribute to cell damage and, ultimately, cell death.
Finally, women, she says, may be at a greater risk of developing the disease not only because of biological factors but also as a result of societal or cultural factors. “Some studies indicate that work and family patterns, which have changed drastically over the last 100 years, may play a role in a woman's memory decline. For example, research has found women who participated in the paid labour force between early adulthood and middle age experienced slower memory decline in late life, building on previous research that associates work and education with higher levels of cognitive engagement.”
Understanding what role these factors play in increasing a woman’s risk of Alzheimer’s is critically important as it would obviously help identify and customize strategies specific to women to prevent, detect, and treat Alzheimer’s and other dementia in the future.
What can women do to minimise their risk of dementia?
Dr. Rebecca M. Edelmayer senior director of scientific engagement for the Alzheimer’s Association says everyone can reduce their risk of cognitive decline by making key lifestyle changes, including regular exercise, staying socially engaged, and maintaining good heart health. She says, for women specifically, “Research is ongoing. This past year, new data presented at the Alzheimer's Association International Conference found strong connections between the experience of hypertensive disorders during pregnancy and cognition later in life. The key takeaway from these findings highlights the importance of prenatal care and monitoring the long-term health of pregnant people as it may impact cognition and dementia risk in later life.”
We have the power to affect cognitive health in age. But we need to start thinking about it whilst we’re young.
