Though dementia affects around 50 million people globally, a number that is tipped to triple in the next 30 years, it affects more women than men.
It is the leading cause of death for women in Australia, so understanding why women are more at risk and how it can be prevented is an important focus of research.
Menstruation, pregnancy and menopause can all affect a woman’s risk of dementia, according to new research.Credit:Getty
Women typically live longer than men, and age is the main risk factor, but it’s more than that. Of the number of people living with dementia globally, women are about 1.7 times more likely to have it than men.
“One of the unique experiences women have to go through is the reproductive lifespan… and fluctuation in female hormones depending on these reproductive events,” says Jessica Gong from The George Institute for Global Health.
Previous research has found that the hormone oestrogen may be neuroprotective and affects the brain regions that are crucial to higher cognitive functions (like memory). But its levels vary depending on reproductive events like menstruation, pregnancy and menopause.
So, for a new study, a research team led by Gong, wanted to examine how the timing of these events might influence the risk of dementia.
The research, published today in PLOS Medicine, looked at the data of 273,240 women without dementia who were part of the large-scale health database UK Biobank.
After adjusting for other factors, including socioeconomic status, ethnicity, smoking, blood pressure, and BMI, they analysed the relationship between the life events that influence oestrogen levels and the risk of dementia over 11 years.
Early menopause and hysterectomy, where internal oestrogen production is cut short, heightened the risk.
“In comparison to 50, which is the average age of menopause, if you have it before the age of 47 [the risk] is 1.32 times higher,” Gong explained. “Having your uterus removed versus not having your uterus removed is 1.12 times higher.”
Starting your first period before the age of 12 increased the risk of dementia later in life by 1.2 times, compared with starting your first period at 13, which is about the average age girls in Australia start menstruation.
But, the strongest risk factor was a younger age at the first live birth. “If you had birth before the age of 21 compared with 25 or 26 it’s about 1.436 times higher [risk],” Gong says.
During pregnancy, the primary form of oestrogen is estriol, not estradiol, which is the form typically known to be neuroprotective. But, Gong says, oestrogen levels may not explain the risk associated with giving birth at a younger age: “It may be possible that having children at a younger age (where the association with dementia risk is the strongest) are linked to other socioeconomic factors and behavioural changes.”
Associate professor Fiona Kumfor, clinical neuropsychologist from the University of Sydney, says that although the role of oestrogen levels in the development of dementia is increasingly being considered by researchers, it is still early days.
“Acknowledging and investigating sex differences is important as we still understand little about what causes dementia, but it is likely to be complex and multifactorial,” says Kumfor, who was not involved with the study.
What that means is that just because you get your first period before 12, had a hysterectomy or early menopause doesn’t mean you will get dementia later in life, explains associate professor Genevieve Steiner-Lim, a NHMRC Emerging Leadership Fellow at the NICM Health Research Institute.
Gong stresses that it is an observational study and some aspects were self-reported, meaning people may have forgotten exact timings or other influencing factors: “We always talk about nature versus nurture.”
Childhood trauma, socioeconomic status and even where you live and your access to gyms, public pools, green spaces and health care as well as air pollution, all contribute to risk.
But although the study findings might seem “quite scary” because we have little control over them, Gong says she doesn’t want women to worry.
Rather the point of the research is to recognise the sex-specific risk for dementia and “ensure the future strategies are sex- and gender-sensitive, to promote health equity”, she says.
For instance, Kumfor says: “Understanding if and how premenopausal hormone use (e.g., via the pill) and hormone replacement therapy impact on later risk or prevention of dementia is an active area of research.”
Still, there are many things we can do to reduce our dementia risk. These include physical activity, not drinking alcohol excessively, quitting smoking, controlling our blood pressure, cholesterol and weight all well as regular social contact with others.
“We know something between 40 and 50 per cent of our dementia risk is modifiable and goes beyond our biological sex and reproductive events in life,” says Steiner-Lim. “There are so many things that are within our control.”
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