THE LANDMARK STUDY, published this week in The Lancet medical journal,
found that if women in the industrialized world breast-fed each of their
children six months longer, they could reduce their chance of breast cancer
by 5 percent, even if they have a strong family history of the disease.
Experts said the findings help explain the discrepancy between low
rates of breast cancer in developing countries and the rising number of
cases in wealthier nations.
"In the developed world there have been enormous changes over the
last 100 years in childbearing patterns and this illustrates that those
changes can explain a great deal of the increase in breast cancer rates,"
said Eugina Calle, director of analytic epidemiology at the American Cancer
Society.
The study involved 200 researchers across the globe examining more
than 47 studies that investigated a total of 150,000 women worldwide. The
analysis of the pooled information was conducted by epidemiologists at
Oxford University in England.
NEW EVIDENCE FOR OLD IDEA
The idea that childbearing is linked to breast cancer dates to
1743, when an Italian researcher called the disease an occupational hazard
of nuns, attributing their relatively high rate of breast cancer to their
childlessness.
Breast cancer rates really started to climb at the end of the 19th
century, and by the 1950s, it was well established that the number of
children a woman had was a major factor in breast cancer.
In 1970, a study found that the age at which a woman had her first
child was key, but that neither the number of children she had nor her
breast-feeding habits mattered.
"Since that time, almost every study on breast cancer has confirmed
that finding on age at first birth, but there's been a lot of confusion
about whether the number of children and breast-feeding had an effect on
breast cancer," said the new study's leader, Valerie Beral, head of the
Oxford epidemiology unit.
Confusion has remained, particularly about the role of
breast-feeding, because individual studies have been too small to provide
answers, she said.
STUDY DETAILS
The Oxford group started by looking at 20,000 women who had only
one child and who had never breast-fed, and compared them with women who
did not breast-feed but continued to have children.
"The risks go down the more children you have. Even if they'd
never breast-fed, the risk of breast cancer went down by 7 percent for
every additional child," Beral said.
The researchers also found that, regardless of the number of
children, the risk of breast cancer dropped by 4.3 percent for every year
the women breast-fed.
"What we have shown is that prolonging breast-feeding and having
more children pushes down breast cancer rates," Beral said.
The magnitude of protection was the same in all women, regardless
of other characteristics, such as ethnic origin, drinking habits and age at
menopause.
In the developed world, women have on average two or three children
and breast-feed each for about two or three months.
And 50 percent of mothers in the United States, about 25 percent in
Europe and about 10 percent in Scandinavia choose not to breast-feed.
A century ago - before oral contraception, infant formula, improved
infant survival and career opportunities for women - Western women used to
have six or seven children and breast-feed each for about two years - a
pattern still dominant in many parts of the developing world.
BREAST CANCER DIVIDE
Today, women in the industrialized world have a 6.3 percent chance
of getting breast cancer by age 70, compared with a 2.7 percent chance for
their counterparts in poor countries.
Part of the reason is that women in poor countries have children
earlier, at about 18 or 19, compared with 23 or 24 in the developed world.
But that couldn't explain all the difference in the breast cancer
rates.
"People have been struggling to fill that gap. Things like diet,
alcohol ... all these things have come up in an attempt to explain the
difference," Beral said. "But, it's prolonging breast-feeding and having
lots of children that really pushes breast cancer rates down.
"There are obviously other determinants, but they are much smaller.
Those two factors account for much of the difference in breast cancer rates
between developed and developing countries," Beral said.
Beral calculated that if western reproductive and breast-feeding
habits mimicked those in poor countries, a woman's breast cancer risk by
the age of 70 would fall from 6.3 per 100 women to about 2.7.
The researchers also calculated what would happen to breast cancer
risk if women still had only two or three children but breast-fed each for
six months longer than the norm of two or three months. That would
translate to a maximum breast-feeding time of nine months per baby.
They found that the chances of breast cancer would decrease from
6.3 percent to 6 percent, a 5 percent drop.
The National Childbirth Trust, which promotes breast-feeding, said
the research clearly shows the benefits for mothers as well as children.
"We hope that this important finding - that the longer women
breast-feed, the more they are protected from breast cancer - will
encourage more women to consider breast-feeding their baby," said Belinda
Phipps, the chief executive of the trust.
The scientists are not sure how childbirth and breast-feeding
reduce breast cancer risk but they believe the findings could pave the way
for better prevention and treatment methods.
***********************************************
To temporarily stop your subscription: set lactnet nomail
To start it again: set lactnet mail (or digest)
To unsubscribe: unsubscribe lactnet
All commands go to [log in to unmask]
The LACTNET mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software together with L-Soft's LSMTP(TM)
mailer for lightning fast mail delivery. For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html
|
