The Number of Kids You Have May Affect Your Lifespan, Study Finds : ScienceAlert

Giving birth to more than the average number of children or having no children at all has been linked to a shorter lifespan and faster biological aging in a recent study led by a team from the University of Helsinki in Finland.

The researchers emphasize that the findings shouldn’t be taken as health advice for individuals. Rather, it’s a population-level association that fits with recent theories around evolutionary biology.

The disposable soma (body) theory, for example, proposes that our lives are a balance between reproduction and survival – if more resources are used for the former, there’s less left for the latter.

“From an evolutionary biology perspective, organisms have limited resources such as time and energy,” says biologist Mikaela Hukkanen, from the University of Helsinki.

“When a large amount of energy is invested in reproduction, it is taken away from bodily maintenance and repair mechanisms, which could reduce lifespan.”

While studies have previously found that having more children is associated with lower wealth later in life, most previous research has involved just one or two variables in isolation – such as the age at which a woman had her first child, or how many children she had in total.

The researchers behind this new study constructed a more comprehensive picture of childbearing history and morality, analyzing data on 14,836 women who were all twins (to help minimize the influence of genetic factors). A subset of 1,054 participants was also assessed for markers of biological aging.

These participants were sorted into seven groups, based on the number of live children they’d given birth to and when they’d given birth.

Statistically, individuals who hadn’t delivered children or who were in the highest group with an average of 6.8 children fared worse in terms of biological aging and mortality risk.

Women who had children early in life also showed signs of faster biological aging and having shorter lives, but this difference mostly disappeared after controlling for other factors, like alcohol consumption and body mass index (BMI). However, the results for childfree women and women with a high number of children held even after taking other factors into account.

The lowest markers of biological aging and mortality risk occurred in the group distinguished by an average number of children – around two to three – and among those who had their pregnancies roughly between the ages of 24 and 38.

The disposable soma theory doesn’t explain why having no children was linked to poorer outcomes. The researchers suggest that variables not measured here – like pre-existing medical conditions – may influence both childbearing and health in later life.

“A person who is biologically older than their calendar age is at a higher risk of death,” says epigeneticist Miina Ollikainen, from the University of Helsinki. “Our results show that life history choices leave a lasting biological imprint that can be measured long before old age.”

“In some of our analyses, having a child at a young age was also associated with biological aging. This too may relate to evolutionary theory, as natural selection may favor earlier reproduction that entails shorter overall generation times, even if it entails health-related costs associated with aging.”

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It’s important to bear in mind that these statistics don’t show direct cause and effect, just an association across a large group of people. That association can be used to develop further biological research and to inform public health strategies.

However, a multitude of other factors affect both lifespan and biological aging, as the researchers are keen to point out. This study should also be considered in the context of other research that shows the benefits of becoming a parent.

“An individual woman should therefore not consider changing her own plans or wishes regarding children based on these findings,” says Ollikainen.

The research has been published in Nature Communications.