Longevity and family size

http://www.newscientist.com/article/dn10875-large-families-linked-to-reduced-parents-lifespan.html

Large families linked to reduced parents' lifespan

10:00 03 January 2007
NewScientist.com news service
Roxanne Khamsi

Parents of large families face a modest increase in the risk of death
compared to those with only a few children, a study of couples married
in the 1800s suggests. And contrary to previous research, the new
report hints that rearing many children can take its toll on fathers,
as well as mothers.

Demographer Ken Smith at the University of Utah in Salt Lake City, US,
and Dustin Penn, at the Austrian Academy of Sciences, mined the
extensive genealogical records kept by the Mormons in the state. The
researchers analysed data from 21,000 couples married in Utah between
1860 and 1895.

Even after adjusting for a woman's age, they found that mothers who
bore more children had shorter lives. For example, more than 5% of
women died within a year of giving birth to any child after their
eleventh. By comparison, about 1% of women died in the year following
the birth of their first, second or third child.

Smith explains that pregnancy can severely deplete the nutrients in a
woman's body, including calcium, and reduce her resistance to
infection. Because of the hardships of the time, these factors might
have put the mothers at greater risk of deadly disease, he speculates.
Previous studies have also suggested that the stress of caring for ill
children can speed up the ageing of mothers' cells (see Chromosomes
aged 10 years by stress).
Widower risk

The analysis also revealed that fathers with more children also had a
shorter lifespan. About 3% of men died within the year following the
birth of any child after their eleventh. On the other hand, less than
1% of men died in the year following the birth of one of their first
three children, even after accounting for their younger age.

The researchers estimate that parents with 12 or more children might
live a year or two less than their counterparts with small families.

Smith notes that the settlers of the Western frontier faced many
hardships in the mid- to late-1800s, including uncertain and limited
food supplies.

"It's a no-brainer – if you are impoverished and have a lot of kids to
feed you're at a disadvantage," says Leonid Gavrilov at the University
of Chicago, US.
Historical value

Gavrilov says that bearing numerous children can perhaps take its toll
on a woman's body even today. But he doubts whether current data would
support a link between large families and reduced paternal lifespan:
"If Bill Gates had 12 children it wouldn't decrease his life
expectancy."

"This is an important study for historical perspective but you cannot
really say anything about modern population because things are so
different in modern times," Gavrilov says.

Smith notes that many parents today opt to have fewer children and to
devote greater resources to each child. "Today there is more of an
emphasis on quality than quantity," Smith notes.

Journal: Proceedings of the National Academy of Sciences (DOI:
10.1073/pnas.0609301103)