From my web page:
Breastfeeding and Breast Cancer
by Katherine Dettwyler, PhD
Department of Anthropology,
Texas A and M University
I looked up the two references [I mentioned in previous e-mail] on
breastfeeding and breast cancer. The first was a study looking at whether
breastfeeding her own children protects a woman against breast cancer. The
reference is:
Newcomb, P.A. et al. 1994. "Lactation and a reduced risk of premenopausal
breast cancer." The New England
Journal of Medicine 330(2):81-87.
In this article, they looked at women who had never lactated, and those who
had lactated for varying lengths of time. If you set the frequency of
premenopausal breast cancer among the women who never lactated at 1.00,
then the relative risk of breast cancer for women who had lactated was:
lactated 3 months or less 0.85
lactated 4-12 months 0.78
lactated 13-24 months 0.66
lactated 24+ months 0.72
for all who lactated 0.78
The authors write: "An increasing duration of lactation was associated with
a statistically significant trend
toward a reduced risk of breast cancer (P < 0.001). Lactation at early ages
and for long durations was
associated with more substantial reductions in risk. If women who do not
breastfeed or who breastfeed for
less than 3 months were to do so for 4 to 12 months, breast cancer among
parous premenopausal women could
be reduced by 11 percent, judging from current rates. If all women with
children lactated for 24 months or
longer, however, then the incidence might be reduced by nearly 25 percent.
This reduction would be even
greater among women who first lactate at an early age."
Newcomb's study is merely the latest in a long series of studies that find
protective effects of breastfeeding
for mothers. It should also be pointed out that many women nurse far longer
than the 24+ month limit in this
study.
The second study I referred to in yesterday's post looked at whether having
been breastfed protected women
from breast cancer when they grew up. This study involved 1,130 women from
two counties in Western New
York. "Breastfeeding" was defined as ANY breastfeeding, so some of these
women may have only been
breastfed for a week or a month, and others for several years. The
reference is:
Freudenheim, J. et al. 1994. "Exposure to breast milk in infancy and the
risk of breast cancer." Epidemiology
5:324-331. (NOTE: epidemiologists use the term "exposure" to refer to both
good and bad factors).
Their results showed:
Health Status Relative Risk
Premenopausal breast cancer if not breastfed 1.00
Premenopausal breast cancer if breastfed 0.76
Postmenopausal breast cancer if not breastfed 1.00
Postmenopausal breast cancer if breastfed 0.73
Thus, for both premenopausal and postmenopausal breast cancer, women who
were breastfed as children, even
if only for a short time, had a 25% lower risk of developing breast cancer
than women who were bottle-fed as
an infant.
Between the two factors, having been breastfed oneself, and breastfeeding
one's own children, one could
reduce the risk of breast cancer by almost half. Now breast cancer strikes
about 1 in 8 women over the course
of their lifetimes. If one could reduce the chances to 1 in 16, that would
be worth doing, I would think. These studies do not promise anyone that
they won't get breast cancer if they were breastfed and breastfeed their
own children, they merely lower the risk by half. Chances are good that you
won't get breast cancer no matter what you do -- as 7 out of 8 women don't.
You can play the odds, or you can change the way you live to reduce your
risk.
It is interesting to look at the steady rise in incidence of breast cancer
over the last few decades in light of this new information. Let me use my
own mother as an example. She was born in 1920, when almost all babies
were still breastfed for several years, and her mother breastfed her. Thus
she got the first type of protection. By the time she started having
children in the late 1940s and up to the mid 1950s, many women were not
breastfeeding their children any more (although my mother did). That means
that there was an entire cohort of women who had been breastfed as infants,
but did not breastfeed their own children. Thus they got the first type of
protection, but not the second. As they aged, they were at greater risk for
breast cancer than their mothers and grandmothers had been (b/c their
mothers and grandmothers had had both types of protection). They you come
to my generation, most of whom were born in the 1950s and 1960s and were
not breastfed as children, so they missed out on the first type of
protection. Then when they started to have kids in the 1970s and 1980s,
many still did not breastfeed their own children, thus missing out on the
second type of protection. As this cohort ages, those who were neither
breastfed nor breastfed their own children are at even greater risk than
their mothers had been. Could it be that the steady erosion of these two
sources of protection account for the steady rise in breast cancer
incidence in the United States over the past 4 decades? At the moment, this
is just speculation based on the timing of the two processes.
------------------------
Additional info from LLLI's CBI handouts "Facts About Breastfeeding"
Enger, S.M. et al. 1997 Breastfeeding history, pregnancy experience and
risk of breast cancer. Br J Cancer 76(1):118-123.
Breastfeeding for at least 16 months substantially reduced the
premenopausal breast cancer risk of women who were not treated for nausea
or vomiting of pregnancy.
Romieu, I. et al. 1996 Breast cancer and lactation history in Mexican
women. Am J Epidemiology 143(6):543-552.
PAROUS WOMEN WHO HAD EVER LACTATED HAD A REDUCTION IN BREAST CANCER RISK,
OR=0.39. DECREASING TRENDS OF BREAST CANCER RISK IN RELATION TO DURATION
OF LACTATION, NUMBER OF CHILDREN BREASTFED, AND WITH LACTATION DURATION FOR
THE FIRST LIVE BIRTH WERE OBSERVED FOR BOTH PRE- AND POST-MENOPAUSAL WOMEN.
POSTMENOPAUSAL WOMEN ALSO SHOWED A SIGNIFICANT DECREASE IN BREAST CANCER
RISK WITH DURATION OF LACTATION WITH THE SECOND LIVE BIRTH.
Hirose, K. et al. 1995 A large-sclae, hospital-based case-control study
of risk factors of breast cancer according to menopausal status. Jpn J
Cancer Res 86:146-154.
The association of breast cancer risk with lactation was more distinguished
in premenopausal women than in postmenopausal women. The protective effect
of lactation was statistically significant among premenopausal women who
breastfed more than six months.
Brinton, L.A. et al. 1995 Breastfeeding and breast cancer risk. Cancer
Causes and Control 6:199-208.
Focusing on women less than 45 years of age, ever having breastfed was
associated with approximately a 10% reduction in breast cancer risk. A
reduction in risk on the order of 30% applied to the small group of women
who had breastfed each child for 72 or more weeks on average.
----------------------------------------------------------------------------
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Katherine A. Dettwyler, Ph.D. email:
[log in to unmask]
Anthropology Department phone: (409) 845-5256
Texas A&M University fax: (409) 845-4070
College Station, TX 77843-4352
http://www.prairienet.org/laleche/dettwyler.html
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