The effects of pregnancy and birth on a woman's body do not dispel with time: New research from Pennsylvania State University (Penn State) has found a connection between the number of times a woman has given birth and the way she has aged, as judged by bodily functions.

The researchers found that any effects on aging weren’t seen until after menopause. “Our findings suggest that pregnancy and birth may contribute to the changing and dysregulation of several different physiological systems that may affect aging once a person is post-menopause,” said Talia Shirazi, a doctoral candidate in biological anthropology at Penn State. Ms. Shirazi gave her comments in a press release from Penn State. Women who are premenopausal are probably protected from premature biological aging because they are still producing ovarian hormones.

Energy in energy out

When women are pregnant, their bodies are biologically tasked, as the growth and housing of the fetus consumes enormous amounts of energy. Breastfeeding is also physiologically demanding. The woman's metabolism, her blood pressure and immune system, among other bodily functions, pay a toll to carry, deliver and feed a baby. The researchers found that women who have given birth, versus those who have not, are more likely to die from kidney disease, high blood pressure and diabetes, to name a few.

Ms. Shirazi, one of the study's authors, discussed in a tweet the pathway to biological aging for these women. Biological aging is the comparison of people of similar chronological ages, who age differently and at different rates.

The sweet spot

To test biological age the researchers looked at metabolic health, kidney and liver health, immune function, inflammation and the health of red blood cells.

The study included a little over 2,000 women. The researchers found that women who had few children, or many children, aged biologically faster. Women who had 3-4 children aged the slowest. But, this relationship was only true in the postmenopausal women.

Women who were aging faster showed signs in all areas. The researchers chalked this up to the extensive effects of pregnancy,

Ms. Shirazi explained in another tweet that their results were slightly surprising and that other studies that looked at cellular age saw differences even in premenopausal women.

She had two explanations. One, that the hormones women make when they are fertile protect them from some of the effects of aging. The other, that "Cellular measures may be more sensitive, and pick up on changes before they result in system-level dysfunction," she wrote in a tweet.

Not just babies

Pregnancy isn’t the only thing that can cause someone to age faster. Things like race, weight and BMI, socioeconomic status, or smoking can all contribute to advanced biological aging. The researchers from Penn State tried to factor these in when they looked at the data.

More than meets the eye

But, the data isn’t everything. The researchers noted that women who have no children, or just one child, might be ill or might have less social support. Illness or lack of social support could also contribute to biological aging. In their paper, they called for more research into the social factors around biological aging.

More than that, they didn’t have access to data on miscarriages, stillbirths or abortions. As many as a fifth of pregnancies, if not more, end in miscarriage, so this could represent a significant source of missing data.

This study was also a cross-sectional study, meaning it was a single snapshot in time. What actually happened to the women in the study as they aged is unknown, as are bigger health complaints that they might have had.

Take away

Until the underlying science is better understood, it is hard to say with any certainty why the number of children someone has affects biological aging. More research can be expected into how pregnancy affects specific areas, like metabolism or liver function, to better understand how bearing, delivering and breastfeeding accelerates aging in women.