Being a Mother to Five or More Children Linked to Alzheimer's Risk in Study

Mothers who give birth to five or more children could have a higher risk of developing Alzheimer's disease, according to a study.

Researchers believe the levels of estrogen, which the body creates during pregnancy, could explain this association.

Alzheimer's disease is the most common form of dementia. Around 5.7million adults in the U.S. are living with the neurodegenerative condition, and two thirds are women - but the reason why is not understood. To shed light on the potential link between motherhood and Alzheimer's, researchers analyzed data from 3,549 women, on factors including their reproductive history. The women were 71 years old and their youngest child was 46 years old, on average.

The data was a combination of information from two independent population based studies in Korea and Greece. Women who had had surgery to remove their ovaries or uterus, or had taken hormone replacement therapy, were excluded from the study.

Participants completed tests to measure their memory and thinking skills to determine whether they had Alzheimer's, or cognitive impairment which could be a precursor to the disease. Of the total participants, 118 developed Alzheimer's and 896 had a mild cognitive impairment.

A study involving over 3,000 women raises questions about the link between pregnancy and dementia. Getty Images

Women who gave birth to five or more children were linked with a 70 percent higher risk of developing Alzheimer's disease than those who had fewer children, according to the results. 59 of the 716 women with five or more children developed the disease, compared with 53 of the 2,751 women with fewer children.

In contrast, women who had lost a fetus were around half as likely to develop Alzheimer's disease as women who hadn't. 47 of the 2,375 women who had an incomplete pregnancy developed the neurodegenerative condition, while 71 of the 1,174 women who had never had such an experience.

Women with more children scored lower on memory and skills tests, while women with one or more incomplete pregnancy performed better that those who hadn't lost a fetus.

However, the authors of the study acknowledged their conclusion might be weakened by the fact the number of incomplete pregnancies may have been underestimated if women did not report abortions, or unknowingly had miscarriages. And data on the cause and timing of such events wasn't collected.

Dr. Ki Woong Kim of the department of neuropsychiatry at Seoul National University, commented in a statement: "Estrogen levels double by the eighth week of pregnancy before climbing to up to 40 times the normal peak level.

"If these results are confirmed in other populations, it is possible that these findings could lead to the development of hormone-based preventive strategies for Alzheimer's disease based on the hormonal changes in the first trimester of pregnancy."

The study was published in the journal Neurology.

Dr. Doug Brown, chief policy and research officer at Alzheimer's Society who was not involved in the research: "These researchers suggest that changing estrogen levels during pregnancy may protect against dementia, but it's a very complex relationship and so far trials using hormone replacement therapy to tackle dementia have been inconclusive.

He stressed: "This research shouldn't give women who've given birth several times any cause for concern; it does highlight interesting links between changing hormone levels and dementia risk, but there are still too many unanswered questions."

Dr. Carol Routledge, director of research at Alzheimer's Research UK, said pregnancy is a complex biological process. "This study lends support to the idea that estrogen or other hormones may have an impact on Alzheimer's risk, but we don't understand the nature of this relationship," she said.

"There will be a wide range of factors associated with having a large number of children, and while the researchers tried to take social and economic status into account in their analysis, it is impossible to rule out non-biological causes for this apparent link."