If going through the pain of labor isn’t enough, a new study published in the journal Human Reproduction seems to suggest that women who give birth age faster than their child-free peers, at least on a cellular level. Apparently, having a child racks up the equivalent of an additional 11 years on this one measure of biological aging and scientists are not so sure why this is.

It all comes down to a compound structure called telomeres: These sit at the end of a chromosome to protect DNA from degeneration, a bit like a lid on a pen. Every time a cell regenerates, the telomeres get a little shorter – in this way, they are the cell's aging clock. Shorter telomeres have been linked to a range of health conditions and higher mortality as well as physical signs of aging like gray hair.

For the study, researchers at George Mason University, Virginia, examined the length of telomeres in the blood samples of almost 2,000 American women aged between 20 and 44, and they made a startling discovery. Those with kids had telomeres that were 4.2 percent shorter on average than those without. This remained true even when differences in age, weight, and socioeconomic backgrounds were offset.

“It is equivalent to around 11 years of accelerated cellular aging,” Anna Pollack, lead author of the paper, told New Scientist.

And it is a more substantial change than you see in studies related to smoking and obesity, she added.

But before you get too concerned or swear off having children altogether, there have been similar studies that suggest the complete opposite. A study on Mayan women in 2017 showed that women who had more children, in fact, had longer telomeres than those who had fewer.

This contradiction led Pollack to speculate that it may have something to do with the stress levels in rearing a child rather than the act of childbirth itself. In particular, she highlighted the lack of mandatory maternity in the US, which could add to the already stressful prospect of raising a newborn.

It seems that for now, at least, more research is needed to confirm this acceleration in cellular aging and determine its extent and cause. In the meantime, Pollack says she doesn't want people to panic. “We’re not saying ‘don’t have children’, she told New Scientist. As the study authors point out, the “findings should be interpreted with caution.”

[H/T: New Scientist]