Why women are more likely to have dementia than men as they age, and how exercise and engagement can help lower your risk

This is the third instalment in a series on dementia, including the research into its causes and treatment, advice for carers, and stories of hope. I am constantly aware that I may develop dementia, the illness that now compromises my mother. One factor that fuels my fear is that I share her gender. Women are far more likely than men to succumb to dementia. Nearly two-thirds of the five million Americans living with Alzheimer’s – the most common form of dementia – 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 men’s? Christopher Beam, an assistant professor of psychology and gerontology at the University of Southern California, offers some insights. He recently published a study which showed that the incidence of dementia and Alzheimer’s disease – that is, the number of new cases at different ages in our lifespans – was about the same in men as women until we reach our mid-80s. At around 85, the rates of any type of dementia – Alzheimer’s disease, vascular dementia, dementia with Lewy bodies (a type of protein build-up in the brain) – begin to decline faster in men than women. For Alzheimer’s disease, which constitutes nearly 75 per cent of dementia cases, the incidence in women diverges earlier in the lifespan. No cure for Alzheimer’s, but we can narrow the odds of developing it We don’t really know why almost 66 per cent of all Alzheimer’s disease cases in the United States are in women, Beam 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.” The US-based Alzheimer’s Association says this view has been long held, but emerging evidence suggests it may not be the whole story. In Beam’s lab, researchers looked into whether genetic variance underlying Alzheimer’s disease differs between men and women. Early research suggested that a gene type known as APOE e4, 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 both. Another hypothesis is that differences in sex hormones explain women’s greater likelihood of an Alzheimer’s diagnosis, Beam says. “We don’t know yet whether oestrogen replacement therapy prevents Alzheimer’s 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 here was to test whether testosterone transfer in the womb helped protect female twins against eventually being diagnosed with Alzheimer’s. The results were heartening because the effect of having a male co-twin for female twins held even after taking into account postnatal hormone exposure. Scientists continue to study the male/female disparity from varying angles – genetic contributions, brain structure, how cells use and metabolise energy, immune system and cardiovascular system differences, life-course hormonal changes, and other biological or social factors. The disparity may indeed be hormone-related, says Dr Rebecca Edelmayer, senior director of scientific engagement for the Alzheimer’s Association. Researchers are exploring the role of the female reproductive cycle. Some studies have found a link between risk of dementia, age at first menstruation, age at menopause, and time between the two. This research, Edelmayer says, “suggests that a longer reproductive period across a life course may decrease one’s risk for dementia”. Researchers are also investigating sex-specific differences in the brain’s architecture. 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 telltale tangles of dementia which may contribute to cell damage and, ultimately, cell death. Women 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, Edelmayer says. “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 took part 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 critical, as it would obviously help identify and customise strategies specific to women to prevent, detect and treat Alzheimer’s and other dementia forms in the future. So what can women do to minimise their risk of dementia? Edelmayer says everyone can reduce their risk of cognitive decline by making key lifestyle changes, including taking regular exercise, staying socially engaged, and maintaining good heart health. For women specifically, she says, research is ongoing. Lisa Marie Presley’s death reminds us to keep hearts healthy – here’s how New data presented at the Alzheimer’s Association International Conference last year found strong connections between the experience of high blood pressure in pregnancy and cognition later in life. “These findings highlight 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,” Edelmayer says. This suggests that we do have the power to affect our cognitive health in older age. But we need to start thinking about it while we’re young. Like what you read? Follow SCMP Lifestyle on Facebook, Twitter and Instagram. You can also sign up for our eNewsletter here.