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
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 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
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).
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
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
The most important aspect of these
experiments is that they show that
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).
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.
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.
People for the Ethical Treatment of Animals (PETA) (
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.
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 growth factor binding proteins in neoplasia (meeting
abstract). Hormones and Growth Factors in Development and Neoplasia,
Fogarty International Conference, June 26-28, 1995, Bethesda, MD,
1995, p. 24
6. Lippman, Marc E. The
development of biological therapies for breast cancer. Science, Vol.
259, January 29, 1993, pp. 631-32
7. Papa, Vincenzo, et al.
Insulin-like growth factor-I receptors are overexpressed and predict a
low risk in human breast cancer. Cancer Research, Vol. 53, 1993, pp.
8. Stoll, B.A. Breast
cancer: further metabolic-endocrine risk markers? British Journal of
Cancer, Vol. 76, No. 12, 1997, pp. 1652-54
9. LeRoith, Derek, et al.
The role of the insulin-like growth factor-I receptor in cancer.
Annals New York Academy of Sciences, Vol. 766, September 7, 1995, pp.
10. Mantzoros, C.S., et al.
Insulin-like growth factor 1 in relation to prostate cancer and benign
prostatic hyperplasia. British Journal of Cancer, Vol. 76, No. 9,
1997, pp. 1115-18
11. Cascinu, S., et al.
Inhibition of tumor cell kinetics and serum insulin growth factor I
levels by octreotide in colorectal cancer patients. Gastroenterology,
Vol. 113, September 1997, pp. 767-72
12. Chan, June M., et al.
Plasma insulin-like growth factor I and prostate cancer risk: a
prospective study. Science, Vol. 279, January 23, 1998, pp. 563-66
13. Epstein, Samuel S.
Unlabeled milk from cows treated with biosynthetic growth hormones: a
case of regulatory abdication. International Journal of Health
Services, Vol. 26, No. 1, 1996, pp. 173-85
14. Epstein, Samuel S.
Potential public health hazards of biosynthetic milk hormones.
International Journal of Health Services, Vol. 20, No. 1, 1990, pp.
15. Epstein, Samuel S.
Questions and answers on synthetic bovine growth hormones.
International Journal of Health Services, Vol. 20, No. 4, 1990, pp.
16. Daughaday, William H.
and Barbano, David M. Bovine somatotropin supplementation of dairy
cows - Is the milk safe? Journal of the American Medical Association,
Vol. 264, August 22/29, 1990, pp. 1003-05
17. Brunner, Eric. Safety of
bovine somatotropin. The Lancet, September 10, 1988, p. 629 (letter to
18. Kronfeld, D.S., et al.
Bovine somatotropin. Journal of the American Medical Association, Vol.
265, March 20, 1991, pp. 1389-91 (letters to the editor)
19. Rubin, Andrew L. and
Goodman, Mark. Milk safety. Science, Vol. 264, May 13, 1993, pp.
889-90 (letters to the editor)
20. Challacombe, D.N., et
al. Safety of milk from cows treated with bovine somatotrophin. The
Lancet, Vol. 344, September 17, 1994, pp. 815-17 (letters to the
21. Coghlan, Andy. Milk
hormone data bottled up for years. New Scientist, October 22, 1994, p.
22. Coghlan, Andy. Arguing
till the cows come home. New Scientist, October 29, 1994, pp. 14-15
23. Mepham, T.B., et al.
Safety of milk from cows treated with bovine somatotrophin. The
Lancet, Vol. 344, July 16, 1994, pp. 197-98 (letter to the editor)
24. Grossman, Charles J.
Genetic engineering and the use of bovine somatotropin. Journal of the
American Medical Association, Vol. 264, August 22/29, 1990, p. 1028
25. Juskevich, Judith C. and
Guyer, C. Greg. Bovine growth hormone: human food safety evaluation.
Science, Vol. 249, August 24, 1990, pp. 875-84
26. Mepham, T.B. Bovine
somatotrophin and public health. British Medical Journal, Vol. 302,
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COMMENT: Some outstanding science
documenting the reasons why you want to avoid drinking milk. Some may
argue that the IGF-1 levels are not increased in organic milk and this
is likely true. However, the IGF-1 is still there, as it is in all
animal milks (and human as well of course). This is one of the reasons
why it is a completely inappropriate food for anyone but a young
child. But there are numerous other reasons to avoid drinking milk
besides the IGF-1 levels (see articles below).
In addition to the possible cancer risk, a
just-published study shows that IGF-1 may play a role in the early
stages of diabetic nephropathy (Horm
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