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by Hans R. Larsen, MSc ChE
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 tumours 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 labelling 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
labelling so that consumers can protect themselves against the very real
cancer risks posed by IGF-1.
From People
for the Ethical Treatment of Animals (PETA) (http://www.peta.com)
References
1. Wilson, Jean D. and Foster,
Daniel W., eds. Williams Textbook of Endocrinology, 8th edition, London,
W.B. Saunders Company, 1992, pp. 1096-1106
2. Cohen, Pinchas, et al. Insulin-like
growth factors (IGFs), IGF receptors, and IGF-binding proteins in primary
cultures of prostate epithelial cells. Journal of Clinical Endocrinology
and Metabolism, Vol. 73, No. 2, 1991, pp. 401-07
3. Rudman, Daniel, et al. Effects
of human growth hormone in men over 60 years old. New England Journal
of Medicine, Vol. 323, July 5, 1990, pp. 1-6
4. LeRoith, Derek, moderator.
Insulin-like growth factors in health and disease. Annals of Internal
Medicine, Vol. 116, May 15, 1992, pp. 854-62
5. Rosenfeld, R.G., et al. Insulin-like
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insulin-like growth factor I and prostate cancer risk: a prospective study.
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