Parents might age faster or slower based on how many kids they have

A new study found that women in Finland who had a lot of kids—or none—aged faster than those with one or a few kids. But the findings don’t necessarily translate to today’s parents

Numerous factors affect how fast we age, from the environment down to our DNA. Even the number of children you have, and when you have them, can alter the aging process and lifespan, a new study finds.

Using historical data on women in Finland, researchers discovered that having five or more children—or no children at all—is associated with faster aging and shorter lifespans, compared with having one to four children. Their findings, detailed in a study published this month in Nature Communications, add new weight to evolutionary biology theories about the trade-off between aging and reproduction.

“As an evolutionary phenomenon, aging is really interesting,” says lead study author Mikaela Hukkanen, a doctoral researcher at the University of Helsinki. “Our finding is sort of surprising, but then again, it’s logical.”

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Hukkanen and her colleagues analyzed data from the Finnish Twin Cohort, a project that has tracked the health of thousands of twin pairs since 1974. They separated 14,836 women from this cohort into six groups based on the number and timing of their childbirths (allowing them to compare genetically similar parents). Then, using lifespan data and blood samples showing aging-linked DNA changes, the researchers modeled how reproduction impacted the aging process of women in each group.

In line with previous findings, members of the cohort who had the most children tended toward shorter lifespans and faster epigenetic aging—changes to how DNA is expressed later in life. This fits with a major evolutionary biology theory known as “disposable soma theory,” which suggests that when organisms put more resources into one aspect of life—such as growth, reproduction or bodily maintenance—it comes at the expense of other areas. Thus, if more resources go to reproduction, it could mean that less time and energy and fewer nutrients are available for maintenance functions such as DNA replication and repair.

The finding that people who didn’t have children also aged faster and had shorter lifespans was more surprising, Hukkanen says. Other researchers in the field say this U-shaped curve representing the relationship between reproduction and aging fits with the data, however.

“I’m seeing more and more [studies] on different measures of aging, and [they’re] starting to converge on the pattern that you see here,” says Calen Ryan, a population epigeneticist at Columbia University, who was not involved in the study.

Some aspects of pregnancy and childrearing are protective of health, lowering the risk of some cancers; for example, breastfeeding lowers the risk of breast and ovarian cancer. Additionally, the increased social support that some parents get when their children are young and the caregiving that they may get from their children later in life may increase their longevity. These benefits might be part of the reason women who did not have children aged faster. But for parents of more than four children, the biological costs may outweigh the benefits.

While the U-shaped curve helps to illuminate how birth and childrearing impacted the study cohort’s aging, the findings don’t necessarily translate to people choosing whether to have kids today, the study authors explain. “I really want to emphasize that this is not a prescription for anyone on how to have your children,” Hukkanen says. “We are just seeing associations and links.... It’s not directly applicable to women having children right now.”

The study focuses on a historical cohort with much different life circumstances than people who might become pregnant today. The participants were born between 1880 and 1957, and some of them lived through several wars and periods of social upheaval in Finland that could have impacted both their health and their opportunities to have children. Also, choosing to be child-free was far less common when members of the study cohort were having children, Hukkanen says, so childlessness in the study might have been more frequently tied to preexisting health conditions that could also impact aging and lifespan.

For people choosing whether to have children today, researchers say differences in social circumstances, health care access and high-quality research on reproductive health could make a big difference on how having—or not having—children impacts the body and aging process. “With the advent of some of these tools to quantify biological aging, we’re starting to be able to measure the impacts of pregnancy in much shorter timescales, which I think is exciting,” Ryan says. “It not only allows us to possibly predict who might be at risk, it also opens the door for clearer pathways to interventions.”