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Breast-Feeding Linked to Lower Cancer Risk

There is new evidence that breast-feeding is associated with a lower incidence of breast cancer among a group of younger women who are at particularly high risk: those with breast cancer in the family.

Although several studies have found that lactation
is protective against breast cancer, the new report found little effect
for premenopausal women over all. But for women with an immediate
relative, like a mother or a sister, who had breast cancer, those who
breast-fed had a 59 percent lower risk of premenopausal breast cancer.
That is closer in line with the risk for women who had no disease in
the family, the study found.

“I was sort of stunned,” said Dr.
Alison M. Stuebe, the first author of the study and an assistant
professor of obstetrics and gynecology at the University of North Carolina,
Chapel Hill. “It’s an impressive reduction in risk. Other studies
either hadn’t looked at this or didn’t include enough women with a
family history to find a statistically significant difference.”

The
new study, published in The Archives of Internal Medicine, used
information from 60,075 participants in the second Harvard Nurses’
Health Study. More research is needed to replicate the findings and to
show that the reduced risk is the result of breast-feeding, rather than
some other factor common to women who breast-feed. But Dr. Stuebe
suggested that breast-feeding may prove just as effective a strategy
for high-risk women as the use of Tamoxifen, a drug that interferes with estrogen activity and is often used in high-risk women to reduce breast cancer risk.

Though
breast-feeding is promoted primarily because it is linked to better
health in babies, mothers seem to accrue long-term advantages. Studies
have found that women who breast-fed are less likely to develop osteoporosis and ovarian cancer, as well as high blood pressure and heart disease decades later.

Because
women who breast-feed tend to be more educated and to have higher
incomes than those who bottle-feed, disentangling the effects of
lactation from those of other habits and behaviors can be difficult.

In
the latest study, the data came from women who participated in the
Nurses’ Health Study from 1997 to 2005. The women had all given birth
and provided detailed information about their habits and medical
history, including breast-feeding, in 1997, before any had developed
breast cancer. About 87 percent of the women had breast-fed for at
least some period. By June 2005, premenopausal breast cancer had been
diagnosed in 608 women. The women who had breast cancer in their
immediate family but who had breast-fed had developed only 41 percent
as many cancers as those who had an affected relative but refrained
from breast-feeding.

But there was no greater benefit if women
breast-fed exclusively or for longer periods of time, raising questions
about the study’s conclusions, said Dr. Louise Brinton, chief of the National Cancer Institute’s hormonal and reproductive epidemiology branch.

“I
would be cautious in interpreting this,” Dr. Brinton said. “You would
expect to see a dose-response relationship with breast-feeding if it is
a really causal protective factor.”

Interestingly, women who
took drugs to prevent the formation of milk were at lower risk for
breast cancer than those who refrained from breast-feeding but did not
use lactation-suppressing drugs, the study found.

LINK: http://www.nytimes.com/2009/08/11/health/research/11cancer.html