Late Motherhood Boosts Family Lifespan - Same Genes Linked To Longevity And Births After Age 45

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.



"If women 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 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.



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 genes 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.



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



-- The study confirmed earlier research showing that women who have
babies late tend to live longer.



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.



-- By looking at the brothers of women who had children late, the
study suggests the same age-slowing genes may be responsible for both
prolonged fertility in women and longer lifespan in both sexes. The
effects of late fertility were strongest for brothers with at least three
sisters because the larger the number of sisters, the more likely it is at
least one will give birth in middle age.



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.




Source
University of Utah