Many factors influence how quickly we age, from our environment to our DNA. The number of children you have and when you have them can also affect your aging process and lifespan, a new study has found.
Using historical data on Finnish women, researchers found that women who had five or more children, or no children, aged faster and lived shorter lives than those who had one to four children. Their findings are detailed in a study published this month. nature communicationsadds new importance to evolutionary biology theories about the trade-off between aging and reproduction.
“As an evolutionary phenomenon, aging is very interesting,” says study lead author Mikaela Hukanen, a postdoctoral researcher at the University of Helsinki. “Our findings are surprising in some ways, but they are also logical.”
Hakkanen and colleagues analyzed data from the Finnish Twin Cohort, a project that has tracked the health of thousands of twins since 1974. They divided the 14,836 women in this cohort into six groups based on the number and timing of their births (allowing comparisons between genetically similar parents). The researchers then used lifespan data and blood samples showing age-related DNA changes to model how reproduction affected the aging process for each group of women.
Consistent with previous findings, members of the cohort who had the most children tended to have shorter lifespans and faster epigenetic aging, which changes the way their DNA is expressed later in life. This is consistent with a major evolutionary biology theory known as the “disposable soma theory.” This theory suggests that when an organism devotes more resources to one aspect of life, such as growth, reproduction, or bodily maintenance, other areas are sacrificed. Therefore, as more resources are used for reproduction, less time, energy, and nutrients may be available for maintenance functions such as DNA replication and repair.
Even more surprising was the finding that childless people also aged faster and lived shorter lives, Hakkanen said. But other researchers in the field say this U-shaped curve representing the relationship between reproduction and aging is consistent with the data.
“It’s becoming more and more visible. [studies] about the different measures of aging, and [they’re] “We’re starting to converge to the pattern we see here,” says Karen Ryan, a population epigenetics researcher at Columbia University who was not involved in the study.
Some aspects of pregnancy and parenting protect your health and reduce your risk of some cancers. For example, breastfeeding reduces the risk of breast and ovarian cancer. Additionally, the increased social support some parents receive when their children are young, and the care they may receive from their children later in life, may extend children’s longevity. These benefits may be part of the reason why women who don’t have children age faster. However, for parents with four or more children, the biological costs may outweigh the benefits.
The U-shaped curve helps reveal how childbearing and parenting affected the aging of the study cohort, but the results do not necessarily translate into people’s choices about whether to have children today, the study authors explain. “I want to emphasize that this is not a prescription for anyone on how to have a child,” Hakkanen says. “We’re just looking at connections and connections. It doesn’t directly apply to women with children at this time.”
This study focuses on historical cohorts with much different living circumstances than those who may 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, which may have affected both their health and their chances of having children. And when study participants had children, choosing not to have them was far less common, Hakkanen said. As such, they say childlessness in the study may have been more frequently linked to pre-existing health conditions that can also affect aging and lifespan.
Researchers say that for people currently choosing whether to have children, differences in social circumstances, access to medical care, and high-quality research on reproductive health can make a big difference in how having children or not having children affects the body and the aging process. “With the advent of some tools to quantify biological aging, we are starting to be able to measure the effects of pregnancy on much shorter time scales, which I think is great,” Ryan says. “This not only allows us to predict who is at risk, but also opens the door to a clearer path to intervention.”
