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Late motherhood boosts family lifespan



For descendants of the Utah and Quebec pioneers studied, "you may be able to look at the ages when your female ancestors gave birth rather than just their longevity in estimating how long you may live," says Smith, whose study will be published online May 4 and in the June 10 print issue of the Journal of Gerontology: Biological Sciences.



  • Women who had "late fertility" a birth at age 45 or older were 14 percent to 17 percent less likely to die during any year after age 50 than women who did not deliver a child after age 40. That confirmed earlier studies. But those studies did not determine if the women gave birth later and lived longer because of genes or because of social and environmental factors such as good nutrition or healthy living.




Smith conducted the study with two other University of Utah researchers: Richard Cawthon, a research associate professor of human genetics, and demographer Geraldine Mineau, a research professor and director of population sciences at the university's Huntsman Cancer Institute, where Smith also is an investigator. Other coauthors were demographer Alain Gagnon and sociologist Ryan Mazan of the University of Western Ontario, and demographer Bertrand Desjardins, of the University of Montreal.

Good Genes Versus a Good Environment

Smith says that during the last decade, "there have been several studies that show a number of species, including humans, are able to reproduce late without medical intervention and those females live longer." Other studies found that late menopause also is associated with women having prolonged fertility and longevity.

"There is a genetic component to longevity, especially for living to very old ages," Smith says. "The new thing here is what most evolutionary biologists long have argued: that survival and reproduction are intrinsically linked to one another. So the novel finding in this paper is discovering this link in humans before modern contraception."

But he says the link between late motherhood and longevity "could be something that is not inherited. It could be good nutrition or really good living, suggesting that if you are a healthier mom you live longer."

That is why the researchers looked at the lifespan of the brothers of women who had babies late, and of those brothers' wives. The wives are not blood relatives, so genetic factors shared by sisters and brothers wouldn't be the same in the brothers' wives.

Smith says the study focused on the longevity of brothers rather than sisters of late-fertile women because "men's own reproductive history doesn't get in the way of assessing the role of their female relatives' fertility."

The study focused on the two pioneer groups not only because of the quality of the data but because of the absence of modern birth control and an unfavorable attitude toward natural family planning methods by Mormons and Catholics. Also, a link between late fertility and lifespan is easier to observe in large families with more sisters.

Since all of those studied are now dead, the researchers could look at the full length of their fertile periods and lives. "Not many data sets could do this," Smith says.

The researchers controlled for various factors that could skew the results. For example, they excluded any individuals who did not live to at least 50 because a husband's death at a younger age would influence his wife's child-bearing.

Late Babies Linked to Longer Life for Moms and Blood Uncles


Compared with women who had their last baby before age 41, Utah pioneer women who had their last baby at age 41 to 44 were 6 percent less likely to die during any given year past age 50, and Utah pioneer women who had their final birth at age 45 or older were 14 percent less likely to die during any given year after age 50.

In other words, imagine woman A had her last baby at age 35, woman B had her last baby at 42 and woman C had her last baby at 46. Then at age 52 or any other age past 50 woman B would be 6 percent less likely to die than woman A, and woman C would be 14 percent less likely to die than woman A.

In Quebec, slightly different age groups were analyzed. Compared with younger mothers, women who had their last child between ages 42 and 44 were 6 percent less likely to die during any given year past age 50, and women who had their last child at age 44 or older were 17 percent less likely to die during any given year past age 50.


So in the Utah group, brothers with three or more sisters at least one of whom gave birth at age 45 or older were 20 percent less likely to die during any given year after age 50 than men without late-fertile sisters.

In Quebec, brothers with three or more sisters at least one of whom gave birth at age 44 or older were almost 23 percent less likely to die during any single year after age 50 than men without sisters who gave birth late.

  • It is possible social and environmental reasons good water, good nutrition, a healthy environment could explain why the brothers and their late-birthing sisters had longer lives. So the researchers also examined the longevity of the brothers' wives.

They found no increase in lifespan, indicating that heredity far more than environmental factors played a role in the prolonged fertility and longer lives of the women, and the longer lives of their brothers.

Smith says the new findings do not conflict with one of his earlier studies finding that having larger families reduced parents' lifespan. Both findings can operate together.


Contact: Lee Siegel
University of Utah

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