A new study has found that multiple pregnancies can make a woman age more quickly. This isn’t just a case of stress-inducing kids giving their mothers more gray hairs, the aging was noted on a cellular level.

As reported this week in the journal Scientific Reports, cellular aging was accelerated by six months to two years for each additional pregnancy, regardless of other factors such as socioeconomic status and diet.

Strangely enough, women who were currently pregnant appeared to have cells that actually looked younger than their biological age would suggest.

“Paradoxically, even though a woman’s biological age was higher with each child that she had, if a woman was pregnant when the measurements were taken, her epigenetic age, and to a lesser extent her telomeres, looked ‘younger’ than predicted for her chronological age,” Christopher Kuzawa, senior author of the study and a professor of anthropology at Northwestern University, explained in a statement.

“It’s an interesting situation in which pregnancy makes someone look temporarily ‘young,’ but there appears to be some lasting, cumulative relationship between the number of pregnancies and more accelerated biological age.”

The researchers took a look at over 800 young women, aged between 20 and 22 years old, with different reproductive histories in the Philippines. Within this cohort, they wanted to see how two separate markers for cellular aging – telomere length and epigenetic age – changed as they underwent pregnancies.

“Telomere length and epigenetic age are cellular markers that independently predict mortality, and both appeared ‘older’ in women who had more pregnancies in their reproductive histories,” added lead author Calen Ryan.

“Even after accounting for other factors that affect cellular aging, the number of pregnancies still came out on top.”

Telomeres are regions at each end of a chromosome (image above). They are a bit like caps that protect the internal regions of chromosomes, preventing important genes from being deleted each time DNA replication takes place. Since they continually get shorter and shorter throughout life, they can be used as a good indicator of cellular aging. Epigenetic age is another estimation of age based on levels of DNA methylation, something that also increases as life passes by.

To dig deeper into this discovery, the researchers have started working on a follow-up study of the same group 13 years after their measurements were taken. They hope to discover whether these changes can still be seen years later and, most importantly, whether the changes can actually affect the person’s wellbeing. 

It’s often been said that having more children, especially more than four or five, can increase a person's risks of certain diseases. This, perhaps, could be a clue as to why.

“It’s not clear whether these relationships will persist into later life as these women age. We also do not know whether these changes will actually lead to less favorable long-term health outcomes," Kuzawa said.