If having children late in life runs in your family, longevity may as well, according to a new analysis drawing from historical data from more than 2 million people.
Dr. Ken R. Smith of the University of Utah, Salt Lake City, and his colleagues found that women who bore children in their 40s and 50s lived longer, and so did their brothers. But their brothers' wives didn't, suggesting that genes, not environment, are likely responsible for the late childbirth-long life connection.
Research has already shown that women who get pregnant and bear children relatively late -- without the help of assisted reproduction technology (ART) -- live longer after menopause, Smith and his team explain in their report in the Journal of Gerontology: Biological Sciences. To learn whether their relatives might live longer too, the researchers looked at records for 11,604 male Utah settlers born between 1800 and 1869 and 6,206 men living in Quebec between 1670 and 1750. All of the men had at least one sister who lived to be at least 50 years old.
These records offer a perfect opportunity to study natural fertility, because women obviously weren't using ART or modern contraception, and in both cultural settings (Mormon and Catholic, respectively) were expected to keep bearing children for as long as they could, Smith told the reporters. "We're observing something that's basically a biological phenomenon," he explained in an interview. "It's not women choosing to have kids late in life, it just simply reflects their ability to have kids late in life."
Among these women, the researchers found, late childbirth indeed conferred longer life. In the sample of 14,123 Utah women, those who had their last child between age 41 and 44 were 6 percent less likely to die during any year after 50 than were women who had children earlier. For those who had babies at 45 or later, annual mortality risk was 14 percent lower.
For the Canadian group of 4,666 women, the numbers were similar. Having a child between 42 and 44.5 reduced annual mortality by 7 percent, and it was 17 percent lower for women who had a child at 44.5 years of age or later.
And their brothers benefited too. The largest effect was seen among men who had at least three sisters, and one sister who had a child late in life. Among the Utah settlers, these men had a 20 percent lower mortality rate; for the Quebec group, mortality was 22 percent lower.
The findings suggest that the genes that allow women to continue bearing children relatively late are related to longevity in both sexes, Smith explained. Today, he added, it's tough to study the effects of late childbirth on longevity. "The modern day sort of analog to the late fertility would be late natural menopause," he said.
Smith and his colleagues are now going to investigate whether late childbirth and longevity are related to life-shortening illnesses like heart disease and cancer. If it turns out there's no disease-specific relationship, but instead a more global influence, that would suggest these genes may have a fundamental role in slowing the aging process, he said.
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