Does pregnancy accelerate "biological aging"?

The research, conducted in the Philippines, used different tools to look at people's epigenetics, the chemical markers associated with their DNA. These markers don't change the basic code of DNA but help control which genes are activated and to what degree. The new study looked specifically at groups of methylene, a type of molecule long associated with different aspects of the aging process. By studying methylation patterns that appear throughout a person's lifetime, scientists have created a number of "epigenetic clocks" that can be used to assess a person's biological age. While chronological age simply reflects how long someone has survived, biological age reflects their physiological status and chances of age-related illness and death.

First study author Calin Ryan, an associate research scientist at the Columbia Center on Aging, said: "What epigenetic clocks do is they serve a predictive function rather than some kind of causal explanation." "They have been trained to predict things that we think represent aspects of aging." So one hour may be designed to predict a person's chronological age, while others predict the likelihood of a person's death, and others estimate the length of their telomeres, which are the protective covers at the end of DNA that prevent them from branching.

The research, published Monday (April 8) in the journal PNAS, used six different genetic clocks to predict the condition of 1,735 young men and women in the Philippines between the ages of 20 and 22. Blood samples were taken for the entire group in 2005. A subset of women – about 330 people – who became pregnant in the years after the first blood sample took a second sample about four to nine years later. The analysis revealed that at all the hours used, women who had been pregnant at least once showed an acceleration in aging compared to women with no pregnancy history. Pregnancies included those that led to miscarriage, stillbirths and live births. This pattern still emerges when scientists have controlled other factors that also affect a person's biological aging rate, such as socioeconomic status, smoking history and certain genetic risk factors. The researchers also found that women with more pregnancies showed faster aging than those with fewer pregnancies "in all six hours," Ryan told Live Science. "We didn't find this relationship between the men we looked at casually." In other words, the number of pregnancies a man does not seem to affect the speed at which his epigenetic clock ticks.

(It's worth noting that men looked biologically older than women in general, regardless of pregnancy status; it's just that people who got pregnant didn't increase men's biological ages higher. This pattern of biological aging in men is constantly seen in epigenetic clock studies and may be linked to men generally dying younger than women, Ryan says.) The team then looked at 330 women who were followed over time, to see if there were differences between the woman's first and second blood samples. In this analysis, an increase in the number of pregnancies was also associated with faster aging compared to fewer pregnancies. However, this pattern appeared in only two of the six hours, specifically the two designed to predict chronological age. Based on all this data, the team estimates that each pregnancy was associated with about 4 to 4.5 months of biological aging among the women in the study.

The results of the study may have been influenced by where it was conducted. For example, people's access to adequate nutrition, health care and social support during pregnancy varies across the Philippines, and these factors may affect how pregnancy affects aging. It is also important that it has been confirmed that most epigenetic clocks work well in tracking aging in white people in developed countries, but many watches still need to be fully validated in people from other populations elsewhere in the world. To further work to derive the effects of parenting on aging from those associated with pregnancy and childbirth.

In addition, Ryan said of the study participants: "These women are very small at the time of taking the sample." So it is not clear whether older women at the time of their first pregnancy will show the same patterns. However, it was useful for the team to study the young women because the researchers were trying to figure out if it was possible to see the biological aging associated with pregnancy earlier, before the health consequences of accelerated age emerged.

Ryan said that if you can detect this accelerating aging early, it could theoretically lead to future treatments to help prevent or reverse the process — though at this early stage of research, it's unclear what these treatments will entail. Similar increases in biological ageing have been seen in some, but not all, other contexts. For example, it was observed among Filipino women in the United States but not among women in Finland. A recent Yale University study found that epigenetic clocks accelerate during pregnancy, but much of this effect disappears after a baby is born, especially in people who are breastfeeding. "So, we have good evidence of accelerating biological aging due to pregnancy, but probably not in all contexts," Ryan said.

Can a pharmaceutical cocktail reverse biological aging?

The study suggests that cells age prematurely in people with depression. For now, this new study is helping scientists begin to uncover the impact of pregnancy on the aging process. However, one day, it could pave the way for medical interventions. "I hope we can start using tools like these [epigenetic clocks] to identify individuals at risk," says Ryan, people who may age with each pregnancy. If they can identify factors that help resist biological aging, scientists could potentially design interventions that mimic those factors in people most at risk.