Parenting already comes with enough unsolicited commentary, so nobody needed a fresh reason to overthink their life choices. Yet here we are, staring at another study suggesting that the number of kids a person has may be linked to how their bodies age over time.

A new study out of Finland found that women with no children and women with a high number of children showed faster biological aging and higher mortality risk than women who had roughly two to three children. The research drew from the Finnish Twin Cohort, covering 14,836 women, with a subset of 1,054 assessed using DNA methylation markers linked to biological aging.

The lowest biological aging and mortality risk appeared among women who had an “average” number of children, around two to three, and whose pregnancies happened roughly between ages 24 and 38. Women in the highest-birth group, averaging 6.8 children, had worse outcomes in the models, and so did women who had no children.

Early childbearing also appeared to be associated with faster biological aging at first, though that connection weakened after researchers accounted for other factors such as body mass index and alcohol use.

The Number of Kids You Have May Affect How Long You Live, Study Finds

There is, of course, a giant catch, because there always is. The researchers were clear that this is a population-level association, not a personal instruction manual for how many children anyone should have. The study looked at Finnish women born between 1880 and 1957, which means it captures a specific group living through very specific social and medical conditions. That makes it useful, interesting, and nowhere near a one-size-fits-all rule for modern life.

The theory behind it comes from evolutionary biology. Biologist Mikaela Hukkanen of the University of Helsinki said, “From an evolutionary biology perspective, organisms have limited resources such as time and energy. When a large amount of energy is invested in reproduction, it is taken away from bodily maintenance and repair mechanisms, which could reduce lifespan.” In other words, the body has finite resources, and reproduction may compete with long-term upkeep.

The strange part of the findings is that women with no kids also had poorer outcomes. The researchers said unmeasured factors, including pre-existing health issues, may help explain that result. Epigeneticist Miina Ollikainen said, “A person who is biologically older than their calendar age is at a higher risk of death,” adding that “life history choices leave a lasting biological imprint that can be measured long before old age.” 

She also stressed that individual women should not change their plans or wishes about children based on this study. Which is probably the sanest part of the entire conversation.