These kinds of contradictions need to be discovered during the early stages of research, said Dan Eisenberg, a biological anthropologist at the University of Washington who works in the area.
"Any research can be wrong even when scientists do everything right," he said. "Part of the way science works is that people address such issues around the world. Then we combine these studies to look at trends and limit what is true. "
Last year, Eisenberg and his colleagues published an article in the journal Scientific Reports, which found that, with each pregnancy, the mother's telomeres appeared to be connected four months to four years older than those of her childless peers.
The Eisenberg study was conducted on over 800 women in their early 20s in Cebu, Philippines. About 60 percent have never had children. The rest have given birth to one or more children.
The study also looked at the epigenetic age of women, a measurement made by examining DNA extracted from white blood cells. By studying the population of cells in DNA, researchers can determine the epigenetic age of a person. The results were similar to those shown by telomeres: The more pregnancies a woman experiences, the older her epigenetic ages are.
"But these are very young women. We do not know if this effect persists with aging. Maybe they just respond with time, "says Kalen Ryan, a Northwestern University biological anthropologist who leads part of the epigenetics of the same study.
Paradoxically, Ryan, Eisenberg and their colleagues found that if a woman was pregnant at the time the measurements made seemed epigenetically "younger" than expected, however, they did not find the same effect when they looked at telomere lengths.
"Why would a woman look epigenetically younger during pregnancy and epigenetically older after pl "Pregnant pregnancy?" Ryan says. "Is it possible for a mom's blood to be contaminated with baby blood or baby blood cells, and if so, it's an artifact of that? These are things we need to understand."
Eisenberg is participating in a new study looking at this, known scientifically as microchimerism, in a subset of the same population of women he previously studied in the Philippines, and would also like to analyze telomere length in women before and after pregnancy to see how it changes.
Some of the results his team finds may be specific to the population in the Philippines, where mothers are younger and fertility rates are "
" We tend to have better health care and good access to health care and less infectious diseases "in the United States, he said." It is not entirely clear whether we will see this clearly in other populations. "
At least one study on telomere lengths of American women has found results from what Eisenberg and Ryan discovered Human Reproduction, the study relies on data from the National Health and Nutrition Examination Survey and looked at telomere lengths in nearly 2,000 American women between the ages of 20 and 44. Researchers found that women who had live births had telomeres
This equates to about 1
1 years of accelerated cellular aging, said Anna Polak, an epidemiologist at George Mason University and a leading researcher on the study. It is striking that this reduction in telomere length is greater than what researchers have found earlier in people who smoke cigarettes or have a high body mass index.
"It was surprising to me that we found such a strong connection," Pollack said. "What we don't know is when exactly the shortening happens," she added. "Is it the first year you are a parent of a baby and you never sleep? And is this due to lack of social support? "
Pablo Nepomnasky, an epidemiologist at Simon Fraser University, believes that the amount of social support a mother receives may be a factor based on his discovery that local Guatemalan women with children actually had longer telomeres of those without. His study, published in PLOS One in 2016, surveyed 75 women from two neighboring rural communities and measured telomere length at two points in 13 years.
"In this indigenous Mayan society in Guatemala, children are considered godparents, a blessing," said Nepomnacki. "Until recently, women were expected to have many children, and in fact there may be a great deal of stress associated with not having children in this society."
Guatemalan women help raise their children, and often the oldest daughter in the family helps to care for them. for the younger ones. He says this extensive support structure is not something many American women have.
This is purely a hypothesis, but community support can reduce maternal stress levels and lead to an increase in telomere length. This may also help to explain the discrepancy between his findings and other studies.
Increased telomere length may also be due to the dramatic increase in estrogen in women who are pregnant, said Nepomnaschy. Estrogen can serve as an antioxidant that prevents telomere shortening. "When you are pregnant, estrogen levels go up," he said. "These prolonged periods of estrogen exposure can protect women from aging."
There are other studies, relying on data collected by the United Biobank and based on neuroimaging, suggesting that as many live births have one woman, " younger, ”her brain looks. The results of the survey are available on the Biobank UK website but have not yet appeared in a peer-reviewed publication.
Eisenberg says that although he believes that it is more likely than pregnancy and childbirth to cause some acceleration as he ages, he does not think it is something to worry about.
"People take risks in life and there are many reasons for people to want to have children," he said. "We already know that creating a child and caring for a child is very difficult – but also very rewarding. Even if it is true that there is a slight acceleration of aging due to children, this does not mean that people would not want to have children. "