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Milk and the Cancer Connection
With complete references for researchers
On January 23, 1998 researchers at the Harvard Medical School released a major
study providing conclusive evidence that IGF-1 is a potent risk factor for
prostate cancer. Should you be concerned? Yes, you certainly should,
particularly if you drink milk produced in the United States.
IGF-1 or insulin-like growth factor 1 is an important hormone which is produced
in the liver and body tissues. It is a polypeptide and consists of 70 amino
acids linked together. All mammals produce IGF-1 molecules very similar in
structure and human and bovine IGF-1 are completely identical. IGF-1 acquired
its name because it has insulin-like activity in fat (adipose) tissue and has a
structure which is very similar to that of proinsulin. The body's production of
IGF-1 is regulated by the human growth hormone and peaks at puberty. IGF-1
production declines with age and is only about half the adult value at the age
of 70 years. IGF-1 is a very powerful hormone which has profound effects even
though its concentration in the blood serum is only about 200 ng/mL or 0.2
millionth of a gram per milliliter(1-4).
IGF-1 and cancer
IGF-1 is known to stimulate the growth of both normal
and cancerous cells(2,5). In 1990 researchers at Stanford University reported
that IGF-1 promotes the growth of prostate cells(2). This was followed by the
discovery that IGF-1 accelerates the growth of breast cancer cells(6-8). In
1995 researchers at the National Institutes of Health reported that IGF-1 plays
a central role in the progression of many childhood cancers and in the growth
of tumors in breast cancer, small cell lung cancer, melanoma, and cancers of
the pancreas and prostate(9). In September 1997 an international team of
researchers reported the first epidemiological evidence that high IGF-1
concentrations are closely linked to an increased risk of prostate cancer(10).
Other researchers provided evidence of IGF-1's link to breast and colon
cancers(10,11).
The January 1998 report by the Harvard researchers confirmed the link between
IGF-1 levels in the blood and the risk of prostate cancer. The effects of IGF-1
concentrations on prostate cancer risk were found to be astoundingly large -
much higher than for any other known risk factor. Men having an IGF- 1 level
between approximately 300 and 500 ng/mL were found to have more than four times
the risk of developing prostate cancer than did men with a level between 100
and 185 ng/mL. The detrimental effect of high IGF-1 levels was particularly
pronounced in men over 60 years of age. In this age group men with the highest
levels of IGF-1 were eight times more likely to develop prostate cancer than
men with low levels. The elevated IGF-1 levels were found to be present several
years before an actual diagnosis of prostate cancer was made(12).
The evidence of a strong link between cancer risk and a high level of IGF-1 is
now indisputable. The question is why do some people have high levels while
others do not? Is it all genetically ordained or could it be that diet or some
other outside factor influences IGF-1 levels? Dr. Samuel Epstein of the
University of Illinois is one scientist who strongly believes so. His 1996
article in the International Journal of Health Sciences clearly warned of the
danger of high levels of IGF-1 contained in milk from cows injected with
synthetic bovine growth hormone (rBGH). He postulated that IGF-1 in rBGH-milk
could be a potential risk factor for breast and gastrointestinal cancers(13).
The milk connection
Bovine growth hormone was first synthesized in the
early 1980s using genetic engineering techniques (recombinant DNA
biotechnology). Small scale industry-sponsored trials showed that it was
effective in increasing milk yields by an average of 14 per cent if injected
into cows every two weeks. In 1985 the Food and Drug Administration (FDA) in
the United States approved the sale of milk from cows treated with rBGH (also
known as BST) in large scale veterinary trials and in 1993 approved commercial
sale of milk from rBGH-injected cows(13-16). At the same time the FDA
prohibited the special labeling of the milk so as to make it impossible for
the consumer to decide whether or not to purchase it(13).
Concerns about the safety of milk from BST-treated cows were raised as early as
1988 by scientists in both England and the United States(14,15,17-22). One of
the main concerns is the high levels of IGF-1 found in milk from treated cows;
estimates vary from twice as high to 10 times higher than in normal cow's
milk(13,14,23). There is also concern that the IGF-1 found in treated milk is
much more potent than that found in regular milk because it seems to be bound
less firmly to its accompanying proteins(13). The concerns were vigorously
attacked by consultants paid by Monsanto, the major manufacturer of rBGH. In an
article published in the Journal of the American Medical Association in August
1990 the consultants claimed that BST-milk was entirely safe for human
consumption(16,24). They pointed out that BST-milk contains no more IGF-1 than
does human breast milk - a somewhat curious argument as very few grown-ups
continue to drink mother's milk throughout their adult life. They also claimed
that IGF-1 would be completely broken down by digestive enzymes and therefore
would have no biological activity in humans(16). Other researchers disagree
with this claim and have warned that IGF-1 may not be totally digested and that
some of it could indeed make its way into the colon and cross the intestinal
wall into the bloodstream. This is of special concern in the case of very young
infants and people who lack digestive enzymes or suffer from protein-related
allergies(13,14,20,22,25).
Researchers at the FDA reported in 1990 that IGF-1 is not destroyed by
pasteurization and that pasteurization actually increases its concentration in
BST-milk. They also confirmed that undigested protein could indeed cross the
intestinal wall in humans and cited tests which showed that oral ingestion of
IGF-1 produced a significant increase in the growth of a group of male rats - a
finding dismissed earlier by the Monsanto scientists(25). The most important
aspect of these experiments is that they show that IGF-1 can indeed enter the
blood stream from the intestines - at least in rats.
Unfortunately, essentially all the scientific data used by the FDA in the
approval process was provided by the manufacturers of rBGH and much of it has
since been questioned by independent scientists. The effect of IGF-1 in
rBGH-milk on human health has never actually been tested and in March 1991
researchers at the National Institutes of Health admitted that it was not known
whether IGF-1 in milk from treated cows could have a local effect on the
esophagus, stomach or intestines(26,27).
Whether IGF-1 in milk is digested and broken down into its constituent amino
acids or whether it enters the intestine intact is a crucial factor. No human
studies have been done on this, but recent research has shown that a very
similar hormone, Epidermal Growth Factor, is protected against digestion when
ingested in the presence of casein, a main component of milk(13,23,28). Thus
there is a distinct possibility that IGF-1 in milk could also avoid digestion
and make its way into the intestine where it could promote colon cancer(13,22).
It is also conceivable that it could cross the intestinal wall in sufficient
amounts to increase the blood level of IGF-1 significantly and thereby increase
the risk of breast and prostate cancers(13,14).
The bottom line
Despite assurances from the FDA and industry-paid
consultants there are now just too many serious questions surrounding the use
of milk from cows treated with synthetic growth hormone to allow its continued
sale. Bovine growth hormone is banned in Australia, New Zealand and Japan. The
European Union has maintained its moratorium on the use of rBGH and milk
products from BST- treated cows are not sold in countries within the Union.
Canada has also so far resisted pressure from the United States and the
biotechnology lobby to approve the use of rBGH commercially. In light of the
serious concerns about the safety of human consumption of milk from BST-treated
cows consumers must maintain their vigilance to ensure that European and
Canadian governments continue to resist the pressure to approve rBGH and that
the FDA in the United States moves immediately to ban rBGH-milk or at least
allow its labeling so that consumers can protect themselves against the very
real cancer risks posed by IGF-1.
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