A recent large-scale study using historical data from nearly 15,000 Finnish women has revealed intriguing links between the number and timing of children and how quickly mothers age biologically.
Published in Nature Communications in January 2026, the research shows that women who had either no children or a high number of children (five or more) experienced faster epigenetic aging and shorter lifespans compared to those with one to four children.
The pattern forms a U-shaped curve, where moderate childbearing appears associated with slower aging and greater longevity. These findings build on evolutionary theories and add nuance to ongoing discussions about reproduction’s long-term effects on health.
The Finnish Twin Cohort Study: Key Discoveries
Researchers from the University of Helsinki analyzed data from the Finnish Twin Cohort, tracking women born between the 1880s and the mid-20th century. By grouping participants into distinct reproductive trajectories based on the number and timing of live births, the team identified six main patterns. Women with two to three children, typically starting around age 27 and spacing births over about five to six years, showed the slowest biological aging and highest survival rates.
Epigenetic clocks, such as GrimAge, measured DNA methylation changes that reflect biological age more accurately than chronological age. Women with the highest number of children (average 6.8) exhibited the most accelerated epigenetic aging, up to 1.35 years faster than those with fewer, later births. Childless women also showed accelerated aging, approximately one year ahead compared to the optimal group, even after adjusting for factors like BMI, smoking, alcohol use, and education.
Mortality risks followed a similar trend. Childless women faced a significantly higher death risk, while those with many children also showed elevated risks. The study adjusted for socioeconomic and lifestyle variables, strengthening the case that reproductive history itself contributes to these outcomes.
Lead researcher Mikaela Hukkanen noted the logical yet surprising nature of the results from an evolutionary perspective. The findings support the idea that reproduction influences aging through resource allocation.
Evolutionary Foundations: The Disposable Soma Theory
The disposable soma theory, proposed in the 1970s, explains aging as a trade-off where organisms allocate limited resources among growth, reproduction, and somatic (body) maintenance. Heavy investment in reproduction reduces resources for DNA repair, immune function, and cellular maintenance, accelerating aging.
In humans, evidence aligns with this framework. Multiple studies have documented a U-shaped relationship between parity (number of children) and longevity. For instance, historical and contemporary data show that extreme parities, either zero or high, correlate with higher mortality. The Finnish study reinforces this pattern using modern epigenetic measures.
While the theory originated in evolutionary biology, human applications remain debated. Some research questions strict trade-offs in modern contexts with better nutrition and healthcare, but population-level data consistently show costs at reproductive extremes.
Why Moderate Childbearing May Offer Advantages
Pregnancy and motherhood provide protective health effects that may contribute to slower aging in women with one to four children. Full-term pregnancies reduce lifetime exposure to hormones like estrogen, linked to lower breast cancer risk. Breastfeeding further amplifies this protection.
According to the World Cancer Research Fund and meta-analyses, every 12 months of breastfeeding reduces breast cancer risk by about 4.3%, in addition to per-birth reductions of around 7%. Breastfeeding also lowers risks for ovarian and endometrial cancers. These benefits stem from hormonal changes during lactation that suppress ovulation and alter estrogen levels.
Social factors play a role, too. Parents often receive support networks from family and community, and adult children may provide caregiving in later life, potentially extending lifespan. Childless women in historical cohorts sometimes lacked these supports, and childlessness was occasionally tied to underlying health issues that independently accelerated aging.
For women with many children, biological costs appear to dominate. Repeated pregnancies demand substantial energy, nutrients, and physiological strain, potentially depleting reserves needed for long-term maintenance. Early or closely spaced births exacerbate this, as seen in groups with accelerated aging from young motherhood.
Limitations and Modern Relevance
The Finnish cohort lived through wars, economic hardship, and limited medical access, circumstances far removed from today’s realities. Childlessness was rarer and often linked to infertility or poor health, unlike current voluntary choices. Modern women benefit from advanced prenatal care, nutrition, and family planning, which may mitigate some costs.
Researchers emphasize that the study shows associations, not causation. Individual decisions about family size should not rely on these population-level findings. As Calen Ryan from Columbia University noted, emerging tools to measure biological aging over shorter periods open possibilities for targeted interventions.
Other studies echo the U-shaped pattern. A UK Biobank analysis found childless women or those with five or more children at higher risk for premature mortality and reduced life expectancy. Historical reviews confirm similar trends across populations.
Broader Implications for Health and Longevity
The research highlights how life history choices leave biological imprints measurable before old age. Epigenetic aging predicts risks for age-related diseases better than calendar age. Understanding reproductive impacts could inform preventive strategies, though much remains context-dependent.
Factors like socioeconomic status, healthcare access, and lifestyle modify outcomes. In resource-rich settings, the protective effects of moderate childbearing may persist, while extremes carry greater risks.
This study advances knowledge of aging’s complexity, blending evolutionary insights with precise biological markers. It underscores that while reproduction shapes health trajectories, modern conditions offer more flexibility than historical ones.
The interplay between family size, timing, and longevity continues to intrigue scientists. As tools evolve, clearer pictures of these trade-offs emerge, offering valuable context for understanding human aging.