The Plain Truth

The Plain Truth
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Wednesday, May 6, 2009

Late motherhood boosts family lifespan

Women who have babies naturally in their 40s or 50s tend to live longer than other women. Now, a new study shows their brothers also live longer, but the brothers' wives do not, suggesting the same genes prolong lifespan and female fertility, and may be more important than social and environmental factors.

University of Utah demographer Ken R. Smith led a new study confirming that women who have their last baby after age 45 live longer than women who have their last baby at younger ages, and also showing that their brothers live longer too. That suggests the same genes promote both prolonged fertility in women and longevity in both sexes. Credit: Jason Smith, University of Utah

"If in your family give birth at older ages, you may well have a chance of living longer than you would otherwise," says the study's lead author, demographer Ken R. Smith, a professor of family and consumer studies at the University of Utah. "If you have a female relative who had children after age 45, then there may be some genetic benefit in your family that will enhance your longevity."

For descendants of the Utah and Quebec pioneers studied, "you may be able to look at the ages when your female 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.

The researchers examined high-quality genealogical records from the Utah Population Database at the University of Utah with its records of 1.6 million Utah Mormon pioneers and their descendants. They also used the University of Montreal's Program on Demographic History Research, which has records on 400,000 people who lived in heavily Catholic Quebec between 1608 and 1850.

Specifically, the study involved the records of 11,604 Utah men who were born between 1800 and 1869 and who had at least one sister who lived at least to age 50; and the records of 6,206 Quebec men who lived between 1670 and 1750, and had at least one sister who lived to 50 or older. The key findings:

  • 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 or because of social and environmental factors such as good nutrition or healthy living.
  • Brothers who had at least three sisters, including at least one sister who gave birth at age 45 or later, were 20 percent to 22 percent less likely to die during any year after age 50 than brothers who had no "late fertile" sisters. That indicates what earlier studies did not, namely, the same genes may influence the lifespan of both sexes and women's ability to give birth at older ages.
  • The brothers' wives didn't have longer lives, suggesting any environmental or social factors that influence lifespan had only a weak influence, and that genes may explain why brothers lived longer when they had a sister who gave birth in her 40s.
The study didn't address how much longevity is due to genetics, but Smith says scientists believe genes account for up to 25 percent of differences in longevity.

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