So far, the results are varied. Some studies report that pregnancy and childbirth dramatically accelerate aging in women at the cellular level. Other research, though, suggests that motherhood and pregnancy may slow down the aging process.
These types of contradictions are bound to be found during the early stages of research, said Dan Eisenberg, a biological anthropologist at the University of Washington, who does work in the area.
“Any single study could be wrong even when the scientists are doing everything right,” he said. “Part of the way that science works is that people look at similar questions all around the world. Then we combine those studies to look at trends and narrow in on what is true.”
Last year, Eisenberg and his colleagues published a paper in the journal Scientific Reports, which found that with each pregnancy a mother’s telomeres appear to be about four months to four years older than those of her peers without children.
Telomeres sit at the end of chromosomes, the threadlike structures that contain our genetic material. Telomeres are kind of like the hard end of shoelaces and serve as a form of protection for the chromosome. When telomeres get too short, cells die and stop replicating. Shorter telomeres are associated with an increased risk of cardiovascular disease, cancer, diabetes and other health conditions. Although telomeres are known to shorten in all humans with age, certain things, such as cigarette smoking, a high body mass index and major stress may accelerate the shortening process. Good sleep, regular exercise and a Mediterranean diet have been associated with longer telomeres.
Eisenberg’s study was conducted on over 800 women in their early 20s in Cebu, Philippines. Roughly 60 percent never had children. The remaining had given birth to one or more children.
The study also looked at the epigenetic age of women, a measurement taken by looking at DNA extracted from white blood cells. By studying the population of cells in the DNA, researchers can determine a person’s epigenetic age. The results were similar to what the telomeres indicated: The more pregnancies a woman went through, the “older” her epigenetic age.
“These are very young women though. We don’t know if this effect persists as they get older. Maybe they just bounce back over time,” said Calen Ryan, a biological anthropologist at Northwestern University who led the epigenetics portion of the same study.
Paradoxically, Ryan, Eisenberg and their colleagues found that if a woman was pregnant at the time the measurements were taken, she looked epigenetically “younger” than expected. However, they did not find the same effect when they looked at telomere length.
“Why would a woman look epigenetically younger during a pregnancy and epigenetically older after multiple pregnancies?” Ryan said. “Could it be that mom’s blood is getting contaminated with baby’s blood, or cells of baby’s blood, and if so is this an artifact of that? These are things we need to understand.”
Eisenberg is involved 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. He would also like to analyze telomere length in women before and after pregnancy, to see how it changes.
Some of the results his team is finding could be specific to the population in the Philippines, where mothers are younger and fertility rates are higher than in the United States, he said.
“We tend to have better health care and better access to health care and less infectious disease” in the United States, he said. “It’s not fully clear whether we’ll see this as clearly in other populations.”
At least one study on telomere length of American women has found results along the lines of what Eisenberg and Ryan found. Published in the journal Human Reproduction, the study relied on data from the National Health and Nutrition Examination Survey and looked at telomere length in nearly 2,000 American women between the ages of 20 and 44. The researchers found that women who had live births had telomeres that were an average of 4.2 percent shorter than their counterparts with no children.
This equates to around 11 years of accelerated cellular aging, said Anna Pollack, an epidemiologist at George Mason University and the lead researcher of the study. Strikingly, this decrease in telomere length is greater than what researchers have previously found in people who smoke cigarettes or have a high body mass index.
“It was surprising to me that we found such a strong association,” Pollack said. “What we don’t know is exactly when the shortening occurs,” she added. “Is it that first year when you’re the parent of an infant and you’re never sleeping? And is it due to a lack of social support?”
Pablo Nepomnaschy, an epidemiologist at Simon Fraser University thinks that the amount of social support a mother gets might be a factor, based on his finding that indigenous women in Guatemala with children actually had longer telomeres than those without. His study, published in PLOS One in 2016, looked at 75 women from two neighboring rural communities and measured telomere length at two points over 13 years.
“In this indigenous Mayan society in Guatemala, children are seen as Godsends, as blessings,” Nepomnaschy said. “Women were expected, until recently, to have many children and in fact, there may be a lot of stress associated with not having children in that society.”
The Guatemalan women help raise one another’s children, and often the oldest daughter in the family helps care for the younger ones. That sort of extensive support structure is not something many American women have, he said.
It is purely hypothesis, he said, but the community support may reduce stress levels in mothers and result in increased telomere length. It could also help explain the discrepancy between his findings and the other studies.
The increased telomere length could also be due to the dramatic increase in estrogen in women who are pregnant, Nepomnaschy said. Estrogen may serve as an antioxidant that prevents the shortening of telomeres. “When you are pregnant your estrogen levels rise up,” he said. “Those prolonged periods of estrogen exposure may be protecting women against aging.”
There is also other research, relying on data collected by the UK Biobank and based on neuroimaging, which suggests that the more live births a woman has, the “younger-looking” her brain looks. Results from the study are available on the UK Biobank website, but have not yet appeared in a peer-reviewed publication.
Eisenberg said that while he thinks it is more likely than not that pregnancy and childbirth do result in some sort of accelerated aging, he doesn’t think it is something to worry about.
“People take risks in life, and there are a lot of reasons people want to have children,” he said. “We already know that gestating a child and taking care of a child is very difficult — but also very worthwhile. Even if it is true, that there is a bit of acceleration of aging as a result of children, it doesn’t mean people wouldn’t want to have children.”