It backs up what generations of mothers have always known – having boys may shorten your lifespan.
Researchers
found that women who had a number of sons lived for an average of eight
and a half months less after completing their family than those who
only had daughters.
The
shorter life expectancy remained regardless of the wealth or social
status of the mothers, the study found. But the gender of the children
made no difference to the father’s life expectancy. The researchers said
this suggests there is a biological reason why women who have only boys
die younger.
Shortened mother's lifespan: Researchers found
that women who had a number of sons lived for an average of eight and a
half months less after completing their family than those who only had
daughters
One theory is that women
expecting boys have more testosterone, which weakens the immune system.
Boys also grow faster in the womb and are usually heavier to carry,
placing more strain on the body.
The research, led by Dr Samuli Helle
of the University of Turku in Finland, was published in the Royal
Society journal Biology Letters. The team looked at the
post-reproductive survival of more than 11,000 mothers in pre-industrial
Finland from parish records kept by the Lutheran Church.
Biological reason: One theory is that women expecting boys have more testosterone, which weakens the immune system
The data was collected from individuals
born in eight different Finnish parishes, covering the 17th to 20th
centuries, when a mostly-agricultural society did not have access to
modern birth-control or medical care.
Dr
Helle said that a mother who had six sons would live for a further 32.4
years on average after the birth of her last child, while a woman who
had daughters could expect to die 33.1 years after her final labour.
He
said: ‘The research shows the more sons you have the lower
post-reproductive survival was. Biologically, there is a bigger cost
associated with having a boy than a girl, so that is one explanation for
the shorter lifespan.’
He
said that ‘social and cultural reasons could also play a factor’, such
as additional support given to mothers by their daughters.
But
Dr Helle suggested that similar effects would be unlikely to be seen in
modern British mothers as family sizes are much lower and nutrition and
medical care have improved greatly.
The
phenomenon, however, may still affect mothers in the developing world. A
study by the University of Manchester found that women who delay having
children into their 30s may live longer than those who become mothers
while young.
The hormone oestrogen – released into the body when a woman becomes pregnant – could help extend lifespan, researchers believe.
Although
oestrogen naturally declines in women over 30, large amounts are
released during pregnancy. It helps keep skin, hair, bones and blood
vessels healthy, and protects against osteoporosis.
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