For decades, researchers have debated how reproduction influences aging.
Does having children shorten a woman’s lifespan?
Does it matter when women have kids?
Or is biology irrelevant?
And are deeper social and genetic forces at play?
A new Finnish study suggests the answer isn’t so simple. And it’s certainly not random as it might appear. Drawing on more than a century of data, researchers report that both extremes of reproductive life are linked to faster aging and higher mortality risk.
Women whose reproductive lives fell closer to the population average, on the other hand, appeared to age more slowly and live longer.
“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,” University of Helsinki doctoral researcher and author Mikaela Hukkanen explained in a statement.
Nature Communications published the findings, which stem from one of the most ambitious efforts yet to connect reproductive history to the biology of aging.
A 100-Year-Old Cohort
The researchers looked at data from the Finnish Twin Cohort, a population-based study that includes women born between 1880 and 1957. All told, the researchers assessed survival outcomes for nearly 15,000 women and examined biological aging in a subset of more than 1,000 participants using DNA methylation, more colloquially known as an “epigenetic clock.”
Unlike earlier studies that focused exclusively on single milestones, the Finnish team reassembled full reproductive histories. Using latent class analysis, the team organized the women into distinct reproductive “trajectories,” based on both the number and timing of childbirths.
Their approach exposed six typical reproductive patterns, ranging from early motherhood with few children, to later motherhood with modest family size, to sustained high fertility across the reproductive lifespan.
The researchers analyzed women who never gave birth as a separate group.
An Unexpected Risk Curve
When researchers compared these reproductive trajectories against mortality data, a startling pattern emerged. Women at both ends of the reproductive spectrum faced elevated risks of death.
Nulliparous women boasted about a 40% higher mortality risk than women with average reproductive patterns. Women with the most number of children, who averaged nearly seven kids, also showed dramatically higher mortality rates.
On the other end of the spectrum, women who’d given birth to two or three kids, typically beginning in their late 20s or early 30s, lived the longest.
Crucially, these links persisted even after the researchers considered other factors, such as smoking, alcohol use, body mass index, education, and shared genetic background (between twins).
“A person who is biologically older than their calendar age is at a higher risk of death. Our results show that life history choices leave a lasting biological imprint that can be measured long before old age,” study lead and senior researcher at the Institute for Molecular Medicine Finland Miina Ollikainen, PhD, elaborated. “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.”
Aging Carved Into the Epigenome
To dig a little deep into the mystery of aging, the team consulted epigenetic clocks. Their primary tool, PCGrimAge, is designed to predict mortality risk years before death.
Here, too, reproductive history factored heavily into the analysis.
- Nulliparous women showed faster epigenetic aging than women who had children later and in moderate numbers.
- Women with the highest lifetime reproductive output also aged faster at the molecular level, showing more than a year of additional biological aging compared with lower-fertility peers.
- Women who became mothers early in life showed signs of accelerated aging as well, though these differences tapered off somewhat after adjusting for external factors.
Notably, epigenetic clocks linked to mortality risk showed the strongest patterns. This, the researchers suggest, hints that reproduction could influence pathways tied specifically to survival.
An Evolutionary Trade-off?
The findings align closely with life-history theory, an evolutionary framework that views reproduction and bodily maintenance as demands that battle for limited biological resources. Under this model – also referred to as the disposable soma theory – energy that the body siphoned off to fuel reproduction might just come at the expense of long-term repair and resilience.
Pregnancy, childbirth, and lactation place heavy physiological demands on the body, especially when repeated many times. At the same time, never reproducing might reflect underlying health vulnerabilities or forego potential protective effects of pregnancy and social support later in life.
Still, the authors stress that these are population-level patterns, not individual-level prescriptions. Reproductive decisions remain the product of multiple influences, such as culture, economics, health, and personal circumstance.
“An individual woman should therefore not consider changing her own plans or wishes regarding children based on these findings,” Ollikainen added.
The authors also point out that the women in this study lived through extraordinary social change, from industrialization to a pair of world wars to the rise and expansion of modern healthcare. The reproductive patterns associated with slower aging also happened to reflect the times – women had two to three children on average, spaced across adulthood.
That perfect storm, the researchers warn, probably reflects both biology and circumstance. Instead, they argue, the study underscores how deeply reproduction, aging, and survival are all tied together. It also reveals how evolutionary pressures and lived realities weave those ties.
Further Reading
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