A new study from the University of Helsinki suggests that both having lots of children — and having none — can speed up biological aging.
The researchers also identified how many children — and under what conditions — are linked to better biological aging and a lower risk of premature death.
The study found that having more children than average — and having no children at all — may accelerate biological aging and shorten a woman’s life.
The team stressed that their findings shouldn’t be taken as recommendations. The results describe a population-level association that aligns with some current theories in evolutionary biology.
For example, the disposable soma theory, proposed by English biologist Thomas Kirkwood, treats aging as the result of an energy trade-off. The theory describes life as a balance between reproduction and survival: if more resources go to reproduction, fewer remain for maintenance. In other words, the body can’t put maximum energy into both reproducing and repairing itself at the same time.
“From an evolutionary biology perspective, organisms have limited resources, such as time and energy. When a large amount of energy is spent on reproduction, it is diverted from the body’s maintenance and repair mechanisms, which can shorten lifespan,” explained biologist Mikaela Hukkanen, the study’s lead author.
Although earlier studies showed that having more children is linked to lower well-being later in life, most of those studies looked at only one or two variables in isolation — for example, the age at first birth or the total number of children someone had.
How the researchers studied the link between number of children and aging
The university team analyzed data from 14,836 female twins to minimize genetic effects. In a subgroup of 1,054 women, the scientists measured markers of biological aging, Science Alert reported.
They divided participants into seven groups based on how many children they’d had and the ages at which they gave birth.
Statistical analysis showed that women who had no children, and those in the group with the largest number of children (an average of 6.8 children), had the worst biological aging measures and the highest mortality risk.
Women who gave birth at a young age also showed signs of accelerated biological aging. That difference largely disappeared after adjusting for factors such as alcohol consumption and body mass index (BMI).
But the results for childless women and women with many children persisted even after accounting for other factors.
And now — here’s the key point: the lowest biological aging scores and mortality risk were found in women who had a moderate number of children — two to three — and in those who first became pregnant between ages 24 and 38.
The disposable soma theory doesn’t explain why having no children is linked to worse aging and lifespan outcomes. The researchers suggested one possible reason: underlying health conditions that both limited fertility and affected later-life health.
“A person who is biologically older than their chronological age faces a higher mortality risk. Our results show that life choices leave a lasting biological mark that can be measured long before old age,” said Miina Ollikainen, coauthor of the study.
The scientists emphasized that many other factors influence biological aging and lifespan. This work should also be viewed alongside studies showing the benefits of parenthood.
“No woman should change her plans or wishes about having children based on these findings,” Ollikainen reassured.
The study was published in the journal Nature Communications.
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