According to new research, the more children a woman has or months spent pregnant reduces the risk of dementia and Alzheimer's.
Having a big family really could slash women's risk of developing dementia decades later, according to new research. The more children a woman has or months spent pregnant reduces the risk of dementia and Alzheimer's. But those who have late puberty, an early menopause or miscarry are at great risk of dementia, studies presented at the Alzheimer's Association International Conference in Chicago.
One study found those with three or more children were an eighth - 12 per cent - less likely to suffer the devastating neurological illness later in life. The finding adds to increasing evidence carrying a child protects against Alzheimer's disease because of the hormonal changes. Alzheimer patients are about twice as likely to be female as male but the reason for the higher rates is a mystery.
A woman's reproductive history is a growing area of interest. Dr Paola Gilsanz, of Kaiser Permanente Northern California Division of Research in Oakland, said: "Possible causes of dementia in women, in particular reproductive factors, are not well understood. In our study, we aimed to identify female-specific risks and protective factors impacting brain health, which is critical to diminishing the disproportionate burden of dementia experienced by women."
Pregnancy was protective even after risk factors in middle and old age such as obesity and stroke were taken into account. The study of 14,595 women aged 40 to 55 between 1964 and 1973 is the first to analyse the link between reproductive history and dementia on such a large scale.
It also found for every miscarriage there was a nine per cent increase in risk compared to those who never suffered one. And those who went through puberty later at 16 or older instead of the average age of 13 were 31 per cent more likely to develop dementia.
What's more those who experienced early menopause at 45 or younger had a 28 per cent higher risk of dementia compared to those who went through it later. The findings shed fresh light on the 'dementia gender gap'. They contradict previous research suggesting HRT (hormone replacement therapy) harms mental skills.
Dr Maria Carrillo, the association's chief science officer, said: "More women than men have Alzheimer's disease or other dementias; almost two-thirds of Americans with Alzheimer's are women." It's estimated of the 5.5 million people age 65 or older with Alzheimer's in the US, 3.4 million are women and two million are men.
Women with shorter reproductive periods of 21 to 30 years were also at 33 per cent more risk of dementia compared to those who remained fertile for 38 to 44 years. The average length was 34 years. The prevailing view why more women have dementia has been they live longer - and older age is the greatest cause. But some research suggests their could be greater due to biological or genetic variations - or even different education, occupation or rates of heart disease.
Dr. Carillo said: "More research is needed in this area because having a better understanding of sex-specific risk factors across the lifespan may help us discover - and eventually apply - specific prevention strategies for different populations of people with Alzheimer's and other dementias."
Another case-control study of 133 elderly British women presented at the same meeting also found those who spent 12.5 percent more months pregnant during their lives reduced their risk of Alzheimer's by a fifth. Study leader Professor Molly Fox, of California University in Los Angeles, said: "We are intrigued by the possibility pregnancy may reorganize the mother's body in ways that could protect her against developing Alzheimer's later in life. These results also suggest that the story might not be so simple as being all about estrogen exposure, as previous researchers have suggested."
Her team believes persisting beneficial effects on the immune system generated during the early stages of pregnancy may be responsible for the observed risk reduction. They collected reproductive history information and measured severity of Alzheimer's disease to evaluate the potential association with pregnancy history and Alzheimer's risk. This identified immune function as the likely protective factor. Other large-scale US studies presented at the conference found no negative effect on the mental health of women who began HRT between the ages of 50 and 54. In contrast, those who initiated it when they were 65 to 79 demonstrated reductions in global cognition, working memory and executive functioning.
Dr. Carey Gleason, of Wisconsin University, said: "These findings add to our understanding of the complex effects of hormones on the brain. These data are sorely needed to guide women's healthcare during and after the menopausal transition and to help women make personalized and informed decisions regarding management of their menopausal symptoms and the prevention of future adverse health outcomes."
Average family sizes have been decreasing in England and Wales since the 1930s, according to the numbers published by the Office for National Statistics. Women who turned 45 in 2016 had an average of 1.9 children - down from 2.21 for their mothers' generation. It's the lowest number on record.
Author: Mark Waghorn
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