The Curious Case of Motherhood and Longevity – Undark Magazine

Ever feel as if motherhood literally sucked the life out of you? Well, theres some science to back that up. A recent study in the journalPLOS One reported that the more children a woman gave birth to, the faster she aged.

Poke around in the literature and you will find as many articles describing the protective effects of childbearing as those that suggest it is utterly depleting.

Thestudy, which looked at DNA in 100 postmenopausal women, found that those whod experienced more pregnancies and births had increased levels of oxidative damage an imbalance between free radicals and antioxidants that is an indication of accelerated cellular aging. The authors declared their findings the first evidence for oxidative stress as a possible cost of reproductive effort in humans.

But wait: Maybe having children revitalizes you, keeps you young. Because the week before that study was published, another had come out in the same journal showing that the more children a woman gave birth to, the more slowly she aged.

Thatstudy, on 94 women with an average age of about 40, found that over the course of 13 years, those who gave birth to more children had longer telomeres, the protective casings at the end of a DNA strand. Like a candle that burns down every time you light it, telomeres get shorter each time a cell divides. The authors suggest that elevated estrogen levels in pregnancy may protect DNA from the damaging effects of oxidative stress.

Individually, such studies make for irresistible headlines, but few news stories acknowledge the persistently contradictory nature of findings in this area. We want the answer to be simple, but it just isnt. Poke around in the literature and you will find as many articles describing the protective effects of childbearing as those that refer to it as utterly depleting.

How could having kids affect health and longevity in such disparate ways? Why cant we definitively say how pregnancy will affect any human body?

I dont think there is a simple answer, says Grazyna Jasienska, head of the Human Reproductive and Evolutionary Ecology group in Poland and a co-author of the study showing accelerated aging in mothers. Its interesting because its complicated.

Nearly 15 years ago, Jasienska established the Mogielica Human Ecology Study Site, which collects data on the inhabitants of five villages in the mountains of southern Poland. Its a rural population in which women still perform a lot of manual labor on small farms. She was attracted to the populations broad fertility rate: from zero to 16 children.

Were comparing women with five kids with women with 12 kids. This makes it possible to really look at the costs of reproduction, Jasienska says.

Life-history theory asserts that since the body has a finite amount of energy to work with, energy put toward reproduction is energy not spent on self-maintenance. Its maternal martyrdom at the cellular level. In most species, increased reproduction is linked to decreased lifespan. This is the theory researchers expect to confirm when studying how childbearing affects longevity in humans, but apparently, it isnt quite that cut and dried.

Although the relationship between womens fertility and their post-reproductive longevity has been extensively studied, the nature of this relationship remains unclear, the authors of yetanotherPLOS Onearticledeclared in December 2015. A meta-analysis of 31 studies on this topic did not show a consistent pattern. The relationship can be negative, positive, or absent.

I was very puzzled, said Pablo Nepomnaschy, about his findings on cellular health among Mayan women in Santa Cruz La Laguna, in the highlands of Guatemala.

Visual by David Samson

Childbearing comes with a vast array of variables: maternal nutrition, disease risk, time between pregnancies, breastfeeding duration, number of pregnancies, even the babys gender. Boys tend to grow faster in utero, to weigh more at birth, and to make higher lactational demands, so having sons may be more energetically expensive for mothers than having daughters, Jasienska explains in The Arc of Life.

And breastfeeding is even more energetically expensive than pregnancy. Women who exclusively breastfeed their babies need to eat an extra 640 calories a day; only 300 additional calories per day are needed during the last two trimesters of pregnancy. Its a factor that tends to be neglected by research into the relationship between fertility and longevity.

The [overall] costs are not the same for someone who eats well compared to someone whose food intake cant cover the excess energy needs of pregnancy and lactation, Jasienska says. [In] well-off women who have many children, we see increases in longevity. For someone in an economically developing country, for example, the costs of reproduction are much more intensely received by the organism.

Childbearing has been shown to increase the risk of cardiovascular disease, diabetes, and osteoporosis, Jasienska noted. Conversely, the hormones involved in pregnancy and lactation can reduce the risk of pancreatic and reproductive cancers. So a womans lifestyle habits and baseline risks for these diseases will all play a part in the ultimate effects of childbearing. Did having kids end your drinking and smoking days, or do your children drive you to drink? According to Jasienska, this is why some studies see no effect: because everything evens out.

Moreover, she says, having a child every year is much different from having, say, one child every four years.The question is: is the damage reversible? For women who have children close together, is [the body] only repairing itself a little, but accumulating damage that leads to problems at an older age?

Not all studies account for all of these variables, but that doesnt mean their findings arent valid, just that we should understand the limits of their broader applicability. To study all of what reproduction does and how Im not sure if a perfect study is possible at all, Jasienska says.

Half a world away, in the highlands of Guatemala, Pablo Nepomnaschy found a population to study with similarly wide-ranging fertility rate: between one and 10 children. Nepomnaschy is the director of the Maternal and Child Health Lab at Simon Fraser University in British Columbia, and co-author of the study that linked childbearing with longer telomeres. He began collecting data on a group of indigenous Kaqchikel Mayan women in 2000, expecting his findings to support life-history theory. Instead, he found the opposite.

I was very puzzled, says Nepomnaschy, speaking from the field in Guatemala. So I had my team redo the results, but they kept coming out the same way I soon discovered we were not the only ones to find these results, but nobody had a good explanation of why.

He says he then happened upon a study in which researchers in Israel found that both mice and humans exhibited faster tissue rejuvenation after pregnancy. The fetal cells that mingle in the mothers organs and bloodstream, the authors suggested, may act like an injection of youth.

I was blown away by [these results] reproduction is costly, but maybe its associated with biological mechanisms that slow down aging, Nepomnaschy said. On average, women live longer than men. So there may be something built into female DNA, or into the process of reproduction, that helps maternal cells recover from being temporarily neglected.

Perhaps its that theres an optimum number of human offspring. A recentanalysis of 18 cohort studies, seven of which included men,uncovered a J-shaped association between number of children and risk of mortality from all causes: Parents of one to five children had a reduced risk of death compared with those who had either no children or at least six. For both men and women, the greatest reduction was for parents of three to four children. Other large studies cite the magic number as two.

Since youd have to start young and have relatively short periods between pregnancies to give birth to six kids, this assessment is in line with Jasienskas concern about the bodys ability to withstand such demands. Another possibility is that the genes linked to increased fertility are also associated with increased levels of oxidative stress, as well as increased susceptibility to infectious diseases.

Pregnancy is one thing: parenting is another. Do social support systems after birth or lack thereof affect a mothers recuperation? Surely decreased sleep and increased stress play roles here, too.

Pregnancy is one thing: parenting is another. Do social support systems affect a mothers recuperation? Surely decreased sleep and increased stress play roles, too.

Nepomnaschy says that as with childbearing, the biological costs and benefits of childrearing may vary by population and counteract each other. Jasienska explains that on one hand, if parents have limited resources and must share them with many kids, this is not going to be good for their health. On the other hand, children help their parents and also take care of aging parents. Our study showed that women with high fertility have shorter life span, but in men, number of daughters is related to longer life span.

Its likely that no study will ever separate out all of the factors to definitively say how pregnancy and parenting affect the body. Especially not if what were looking for is a simple answer an irresistible headline that purports to be applicable to anyone.

Olivia Campbell, a science journalist and essayist, is a regular contributor atNew YorkMagazine. Her work has also appeared in The WashingtonPost, Scientific American, Quartz, VICE,Pacific Standard,and STAT News.

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The Curious Case of Motherhood and Longevity - Undark Magazine