"We were surprised to find such a striking result," epidemiologist Anna Pollack from George Mason University told New Scientist.
"It is equivalent to around 11 years of accelerated cellular ageing.".
Pollack and her team analysed data from the National Health and Nutrition Examination Survey (NHANES) – a broad cross-sectional study charting the wellness of people in the US over time.
When they examined data from the period 1999–2002 – years in which the survey included measurements of a genetic marker called telomeres – they noticed something unusual.
What's more, in the study, the telomere shortening seemed to vary depending on how many children the women had delivered.
At least one researcher not involved with the study has suggested the effect might be as little as three years of biological ageing.
"We're not saying 'don't have children'," Pollack told New Scientist, and while scientists keep examining what's really going on here, that's very level-headed advice. »