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September 10, 2002
HRT, Drinking Milk Tied to Higher Levels of a Cancer-Promoting Hormone (IGF-1) in Women
By Suzanne Rostler
NEW YORK, NY, USA (Reuters Health) - Drinking milk may raise blood levels of IGF-1, a cancer-promoting hormone,
in women, according to two recent studies. What's more, taking hormone replacement therapy (HRT) or having multiple
children appears to reduce levels of the hormone.
But it is too soon to recommend that women avoid milk products, since it is not clear whether milk, or a particular
component of milk, is the culprit, the study authors point out. Similarly, more research is needed into the effects
of HRT on cancer risk, since a large study recently found that taking HRT increased the risk of breast cancer,
they note.
"We cannot yet make the leap to say that higher levels of milk intake will increase the risk of cancer,"
Dr. Michelle D. Holmes, the primary investigator of both reports, told Reuters Health. "Foods are complicated,
with many components, and they may have many different actions on the body."
The data on more than 1,000 women analyzed in both reports was drawn from the Nurses' Health Study, the longest
national health study conducted in women. The findings are published in the September 2002 issue of Cancer Epidemiology
Biomarkers and Prevention.
One report found that levels of insulin-like growth factor-1 (IGF-1), a hormone that can raise cancer risk when
levels are too high, fell as the number of pregnancies increased. Women who had been through at least four pregnancies
had IGF-1 levels that were 14% lower on average than their peers who had fewer children.
Pregnancy is known to decrease a woman's risk of breast and colon cancer, and the study--the first to report an
association between parity (the number of times a woman has given birth) and IGF-1 levels--suggests a possible
mechanism behind this effect.
However, more research is needed, cautioned Holmes, from Brigham and Women's Hospital in Boston, Massachusetts.
"If this connection between parity and IGF levels should turn out to be consistent in other similar studies,
it would be interesting to know something about how parity affects IGF levels over time," she said in an interview.
Her study also reported a link between HRT, especially oral estrogen, and lower IGF-1 levels among postmenopausal
women, a finding that supports the results of other studies. Women using oral estrogen had lower levels than those
using the estrogen skin patch and women who did not use any hormones.
A second study found that IGF-1 levels rose in tandem with women's intake of protein, especially from milk.
There was no association between IGF-1 levels and vegetable protein intake. Yogurt, cheese, and ice cream also
had no association with the hormone.
Taken together, the study findings suggest a link between lifestyle factors and levels of a hormone associated
with cancer risk.
"For something like milk intake, it means we have a potential mechanism, but we do not yet know whether there
is a connection between milk intake and cancer risk," Holmes explained.
"For something like parity...this may represent a mechanism by which parity helps prevent cancer. As scientists,
it is always more reassuring if we know how something works rather than just knowing that it works," she added.
OCA note: This article fails to mention that Bovine Growth Hormone, rBGH, (which is
given to US dairy cows to increase their milk production) substantially raises the levels of IGF-1 in milk. See
our rBGH page.
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