▎ WuXi AppTec content team editor
Dementia is a disease that seriously impairs the quality of life, brain health and longevity of the elderly, and can also affect the entire family. Currently, about 50 million people worldwide have dementia, and this number is expected to triple by 2050.
Women are more susceptible to dementia than men. Studies have found that men have a 19% to 29% lower prevalence of dementia than women.
Scientists have analyzed that women's greater susceptibility to dementia is not only related to longer lifespans, but also related to some factors specific to women, such as fertility and estrogen levels, which may also play a role.
According to a study published in PLOS Medicine, female reproductive and hormonal factors, including menarche, natural menopause and the age of first childbearing, the length of childbearing period (from menarche to natural menopause), hysterectomy, oral contraceptives, etc., may be associated with an increased or decreased risk of dementia.
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The study analysed data from the UK Biobank and included 273,240 female participants with an average age of 56.
The researchers counted basic health information such as the participants' height and weight; lifestyle information such as smoking status and alcohol consumption; health indicators such as blood pressure and blood lipids; family history and treatment history of chronic diseases such as hypertension; and information on factors related to fertility, including menarche, menopause, first birth (live birth) and pregnancy age, fertility period, miscarriage and number of births, age of hysterectomy and oophorectomy, age at which oral contraceptives were initiated, and age and duration of estrogen replacement therapy.
The researchers found that the average ages of participants at menarche and first childbearing were 13 and 26, respectively; 85 percent were at least 1 pregnancy; 44 percent had 2 children; 81 percent had taken oral contraceptives; and 38 percent had undergone estrogen replacement therapy, starting at an average age of 47 and the average duration of treatment was 6.3 years.
61% of the participants were natural menopause, with an average age of 50 at menopause. Among the participants who had menopause due to surgery, 19% and 8% underwent hysterectomy and oophorectomy, respectively.
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During the 12-year follow-up period, a total of 1866 women developed dementia.
After removing other factors, the researchers found that pregnancy, longer fertility periods, oral contraceptives, and older age at natural menopause were associated with a reduced risk of dementia in women, while younger at first birth, younger or older at menarche, younger at natural menopause, and having had a hysterectomy were all associated with an increased risk of dementia.
Compared with participants who did not become pregnant, participants with a history of pregnancy had a 15% lower risk of dementia.
Compared with participants with a reproductive period of < 33 years, participants with a fertility period of 36-37 years, 38-39 years, 40-42 years and > 42 years had a 22%, 33%, 32% and 20% reduction in dementia risk, respectively.
Participants who had taken the pill had a 20 percent lower risk of dementia compared to those who did not take the pill.
Compared with participants aged 50 at natural menopause, participants aged < 47 years of age at natural menopause had a 32% increased risk of dementia, while participants aged 51-52 and 53-54 years at natural menopause had a 20% and 24% reduction in dementia risk, respectively.
Compared with participants aged 25-26 at the time of first childbirth, participants aged < 21, 21-22 and 23-24 years old at first childbearing had an increased risk of dementia by 43%, 23% and 21%, respectively.
Compared with participants aged 13 at menarche, participants aged < 12 and > 14 years old had an increased risk of dementia by 20% and 19%, respectively.
Compared to participants who had not had a hysterectomy, the risk of dementia increased by 12 percent.
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The researchers analyzed that factors associated with fertility, the effect on the risk of dementia, may be related to estrogen changes. Estrogen can play a protective or harmful role in the nervous system, depending on the concentration and form of estrogen.
Throughout a woman's life, estrogen in the body changes. During childbearing, estradiol (E2) is the predominant form of estrogen; during pregnancy, estriol (E3) is the predominant estrogen. At the same time, the use of exogenous hormones, such as oral contraceptives, can also affect women's estrogen levels.
However, the definitive mechanism by which estrogen changes affect the risk of dementia has not yet been defined and more research is needed.
Since this study is observational, it only shows an association between different fertility factors and dementia risk, and does not show a causal relationship. Moreover, the study also has some limitations, and some of the data rely on participant recalls, etc., which may also have an impact on the results of the study.
The study concludes by highlighting that to date, there is no effective treatment for dementia. Therefore, reducing or changing risk factors plays an important role in preventing the occurrence of dementia. While women are more susceptible to dementia than men, finding out which risk factors are influencing and taking preventive measures will help promote women's brain health and improve quality of life.