How Childbearing Leaves Its Imprint on Mothers’ Biological Age

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Hsaving children is expensive. Not just financially, but also biologically. At least in theory. Evolutionary biologists suggest that bodies may have limited energy to share between reproduction and long-term maintenance.

Now a team of Finnish scientists has used decades of data from a large twin study of 15,000 women to ask whether the childbearing cycle (how many children a woman has and when she has them) might influence how quickly she ages. Study participants were asked to complete a survey in 1975 and their lives were tracked through 2020.

Researchers from the University of Helsinki and the Minerva Foundation Medical Research Institute discovered a U-shaped pattern. Women who had two or three children and gave birth between the ages of 24 and 38 fared better. Women who had too much or too little were worst off. The scientists controlled for smoking, alcohol consumption, weight and education and published their results in Natural communications.

“From an evolutionary biology perspective, organisms have limited resources such as time and energy,” explained doctoral student and co-author Mikaela Hukkanen, in a statement. “When a large amount of energy is invested in reproduction, it is taken away from the body’s maintenance and repair mechanisms, which could reduce lifespan.”

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Having more than four children, in particular, was associated with a shorter-than-average lifespan and more accelerated biological aging. Women without children also age more quickly than women with a few children, although the researchers suggest that this unexpected finding could be explained by other lifestyle or health factors that were not taken into account by the study: underlying health conditions that might have reduced fertility, different social support systems later in life, or different disease risks. For example, certain types of pregnancies or breastfeeding patterns can affect cancer risk.

The researchers were quick to point out that the findings do not suggest that certain childbirth ages or numbers of pregnancies actually lead to healthier aging, nor that women should shape their reproductive choices based on these findings, especially as the number of children women have today has declined and the age of first birth has increased. (The twins in the study were born between 1880 and 1957.)

“A woman should therefore not consider changing her own plans or wishes regarding children based on these results,” said study author Miina Ollikainen.

The results, which took into account biological markers of aging from blood samples, confirm previous findings based on mortality data. According to these epigenetic blood markers, women who had many children or did not have any children were biologically slightly older than their chronological age. Women who had children very young were also more likely to have an accelerated biological age.

“Our results show that life history choices leave a lasting biological imprint that can be measured well before old age,” added Miina Ollikainen.

In this twin cohort at least, the price of motherhood was extreme. The middle ground in child-rearing seemed like the safest deal in the long run.

Main image: DOERS / Shutterstock

• Kristen French

  Published on January 12, 2026

  Kristen French is an associate editor at Nautilus. She has worked in science journalism since 2013, reporting and writing articles and news for publications such as Wired, Backchannel, The Verge, And New York Review. She holds a master’s degree in science journalism from Columbia University.