More children could translate into a shorter life for both mothers and fathers, according to new research from a University of Utah professor.
The study, which will be published in the January issue of The Proceedings of the National Academy of Science, shows both women and men have a higher chance of dying young if they have larger families. That risk is especially high for women, who drastically increase their chance of dying earlier when they have had more than four children, the study states.
The study, led by U. professor Ken Smith, analyzed data from nearly 22,000 couples from the Utah Population Database who were married between 1860 and 1895. While childbirth has changed since then, Smith said the toll on female bodies by producing large numbers of children still exists today. Perhaps more surprising, he added, men also
showed an increased mortality rate corresponding to the number of children they fathered, although it is much less than the impact on women.
"These kinds of fertility patterns and survival patterns are still present today in developing countries. It's not like these stresses and costs associated with having children have disappeared from the planet because it's the 21st century," said Smith, a professor of family and consumer studies at the U.
Women in the study who had from one to three children had about a 98.5 percent survival rate in the year following their last child's birth. That rate dropped to roughly 95.5 percent for women who had seven to 11 children and dipped to 94 percent for women bearing more than 12 children.
Those patterns were similar for men, although much less drastic, dipping from a 99.5 percent survival rate for men with one to three children to a 97.5 rate for men with more than 12 children.
While modern medical advances may mitigate some of the risks of death following childbirth, Smith said that same progress has allowed women to continue having children into their late 30s and 40s. Those women have a much higher risk of dying within a year after their last child is born, he said.
Smith added, however, that the study is not an attempt to peg the number of children as the direct cause of shorter lifespans among women. Women who have more children may be more likely to die after their last is born simply because they are older by the time they are finished bearing children, for example.
But Smith added the fact that women with more children are more likely than men to die within a year of their last birth does hint at the relationship between increased reproduction and mortality.
"Our results are consistent with the idea that reproduction requires a trade-off between quality and quantity, and may help explain the evolution of menopause as a means of increasing mother survival," he said.
Unlike almost all other species, human females go through menopause, which could be an evolutionary reaction to the greater risk of death with childbearing later in life, Smith said.
"We're pushing artificially through contraception and delayed marriage. We're pushing the fertility schedule to these later ages where there are more problems," he said. "From an evolutionary standpoint, menopause exists in humans because having kids at these old ages was not a benefit to the species."
Utah women produce an average of 2.7 children in their lifetime, Smith noted, compared with the 2.1 national average.
Smith said the study is not meant to attack the larger family sizes in Utah, but rather to take a peek at the relationships between how people reproduce and their length of life.
"We're not attaching any value judgment to it. I can see where people might be upset and take it like we're out to criticize large families, but that is not our intent," Smith said.
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