Our mothers might be onto something when they jokingly blame us for their gray hair and wrinkles. In two recent studies, DNA methylation-based epigenetic clocks show that pregnancy, with its far-ranging emotional and physical changes, increases the biological ages of mothers. On the bright side, the effects were reversible in those who breastfed, according to one of the studies.
The Biological Cost of Pregnancy
Buying a crib, diapers, and other necessities can rack up the bills, but preparing for baby also has a biological cost. A hint of this was born last year when a group analyzed DNA methylation with epigenetic clocks before and after several stressful conditions. They reported that pregnancy boosted biological age in mice and in a sample of 14 women, but the effect was transient—it reversed when the pup or baby was born.
To multiply their understanding of this process, Calen Ryan et al. (Columbia University) studied a group of 825 women and 910 men born in the same year in the Philippines. About 40% of the 21-year-old women had been pregnant at least once before the study started. The team tested blood samples for DNA methylation and analyzed the data with six epigenetic clocks. Here’s what they found:
- Women who had been pregnant at least once had biologically aged a few months to about a year faster than those who had not been pregnant
- With each pregnancy, a woman’s biological age increased by a few months compared to women with fewer or no pregnancies
- Perhaps unsurprisingly, fathering a child had no effect on the biological ages of the men
The team kept up with the women for up to nine years later. As the women became pregnant for the last time during the study period, the researchers again took blood samples. The findings weren’t as clear-cut this time—here’s what they found:
- Women who had been pregnant multiple times since the beginning of the study had aged a couple of months with each occurrence, but only according to two of the six clocks
Potential limitations are that the researchers didn’t specifically address potential reversibility of the aging effect, or whether factors like breastfeeding and body mass index (BMI) affected aging. That’s what the next paper covered…
If I Could Turn Back Time
Conceived by the lab of Kieran O’Donnell (Yale School of Medicine), the other investigation involved the use of five epigenetic clocks to analyze DNA methylation in a group of 119 women in the early, mid, and late stages of pregnancy in California. They also followed up 3 months after birth in a smaller subset of 68 women. Here’s what they found:
- Throughout pregnancy, women biologically aged about 1-2.5 years, depending on the clock used
- At 3 months after birth, the effect reversed by as much as 8 years for some women; overall, the decrease in age after giving birth was about 2-3 times the increase in age during pregnancy
- Having a high pre-pregnancy BMI hindered the reversal
- Exclusive breastfeeding was associated with a steep decline in postpartum biological age
Although this team looked at the reversal of aging after giving birth, they didn’t examine the effect of multiple pregnancies or compare these subjects with women who didn’t become pregnant, as the other paper did.
The Bottom Line
Wrapping up, the studies suggest that pregnancy ages women, though it may be reversible. But because the two papers examined diverse sets of factors at differing time points in distinct populations of women, both groups say many questions remain.
“We still have a lot to learn about the role of pregnancy and other aspects of reproduction in the aging process,” says Ryan. “We also do not know the extent to which accelerated epigenetic aging in these particular individuals will manifest as poor health or mortality decades later in life.”
So, call your mother, and then dive into the details of the Ryan team paper (PNAS, April 2024) and the O’Donnell team paper (Cell Metabolism, May 2024).