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For decades, scientists have debated whether having children comes at a biological cost later in life.
The theory is straightforward: pregnancy and raising offspring require significant energy and resources, potentially accelerating aging and increasing vulnerability to health problems in old age.
But a new study of aging dogs, published in The Journals of Gerontology, Series A: Biological Sciences and Medical Sciences, has challenged that idea, finding that motherhood was linked not to greater frailty, but to better health in later life.
Researchers from the Gerald P. Murphy Cancer Foundation’s Center for Exceptional Longevity Studies used companion dogs as a model to investigate the relationship between reproduction and aging.
The team focused on 95 elderly female Rottweilers and assessed frailty using a 34-item clinical index that measures the accumulation of health deficits over time.
Rather than examining lifespan alone, researchers looked at what they called “late-life robustness”—a measure of how well the dogs maintained their health as they aged.
According to life-history theory, reproduction should place strain on the body by diverting resources away from maintenance and repair.
Under that framework, mothers would be expected to show more signs of age-related decline than females that never had offspring.
The results pointed in the opposite direction.
Female dogs that had produced live offspring were more than three times as likely to retain late-life robustness compared with dogs that had never given birth.
Even more surprisingly, females with the greatest number of litters showed the highest levels of robustness in old age.
Ali Smith, a canine behavior consultant, told Newsweek the findings should be interpreted cautiously when considering humans.
While dogs and humans are both mammals and may share some quality-of-life factors, she said there are major biological and lifestyle differences between the two species.
“The gestation period for dogs is 63 days and humans, it’s for 280,” Smith said. “A human mother carries her baby for around 14 weeks longer than a dog does. That takes a toll.”
Smith also noted that puppies typically leave their mothers at around eight weeks of age, meaning the demands of motherhood are far shorter than they are for human parents.
The researchers also tested whether the results could simply reflect differences in health earlier in life.
They examined measures including previous health deficits and lifetime disease profiles but found these factors could not adequately explain the association.
The findings may have implications beyond the canine world.
Previous studies in women have produced mixed results, with some suggesting higher numbers of births may increase frailty later in life and others finding little evidence of a biological cost.
A large body of research has also failed to consistently show that motherhood shortens lifespan.
The authors argue that dogs provide a useful model for exploring the question because they share many environmental influences with humans while avoiding some of the social and behavioral factors that can complicate human studies.
While the research does not prove that motherhood protects against aging in people, it raises intriguing questions about the biological relationship between reproduction and long-term health.
The researchers suggest that having offspring may, in some circumstances, help dampen the development of frailty later in life.
They say future studies should investigate the genetic and epigenetic mechanisms that might explain the unexpected link.
For Smith, one of the most important unanswered questions is how access to care before and after birth influences long-term health.
“The biggest question this raises is how important proper care and recognition is before and after birth, and the long term implications of that,” she said. “That’s one thing those dogs absolutely did have—appropriate, strong care and support throughout the entire process.”
The study offers a surprising twist on a long-standing assumption: motherhood may not always exact the biological price researchers once expected.
Reference
Waters, D.J., Maras, A.H., Rong, F., Carrillo, A.E., Chiang, E.C. and Suckow, C.L. (2026). The relationship between parity and late-life frailty: companion dogs as a preclinical model for evaluating factors that aggravate or mitigate the frailty cost of reproduction. The Journals of Gerontology: Series A, [online] 81(8). Available at: https://academic.oup.com/biomedgerontology/article/81/8/glag163/8738328 [Accessed 22 July 2026].
Contact Newsweek editors on this story: Kara Dolman and Gray R. Thomas
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