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Human health concerns
Most countries, including Canada and the European Union, have not approved rbST
for use due to public health and animal welfare concerns.
Proponents of rBGH use claim that this disapproval is an attempt to impose
unfair trade restrictions.
BGH proponents argue that cross-species differences are significant enough to
prevent most cross-species effects. (i.e. bST does not "work" in humans.)
Monsanto, the largest single producer of rBGH has repeatedly stated that the
amounts are too small and digestion too complete for them to have any direct
effect in humans. They state that there is no scientifically verifiable
difference between milk from treated versus untreated cattle.
According to Monsanto and the various government regulatory bodies which have
reviewed rbST, milk and meat from cattle supplemented with rbST are safe.
Monsanto also states that the only difference between milk from supplemented
cattle and unsupplemented cattle is the amount of insulin growth factor 1
(IGF-1) — and that there is not even a difference in the concentration of bST.
Opponents counter that indeed there are differences aside from the higher rate
of IGF-1, most importantly that BGH and rBGH (rbST) have a different chain of
amino acids. This difference "can markedly change the immunogenic
characteristics of a protein". Whether the change in immunogenic characteristics
brought about by rBGH actually poses a threat to consumer health has yet to be
demonstrated.
Canada's health board, Health Canada, commissioned a study which found "no
biologically plausible reason for concern about human safety if rbST were to be
approved for sale in Canada. The only exception to this statement is (possible
hypersensitivity)."
Although IGF-1 is important for normal development, some studies found that
IGF-1 levels in the human blood stream are elevated in patients with breast,
prostate or colorectal cancer.
In 1998, the American Cancer Society reported a correlation between human blood
levels of IGF-1 (often associated with obesity) and breast cancer, prostate
cancer, and colorectal cancer.
Increased plasma levels of IGF-1 are associated with a higher risk of diabetes
and a shorter lifespan in animal studies (e.g. Nature, vol 444, pages 337-342,
2006).
On May 22, 2006, Scientific American reported that Dr Gary Steinman of the Long
Island Jewish Medical Centre published a paper in the Journal of Reproductive
Medicine proposing a link between IGF and the incidence of twin births. He cites
the May 6 issue of The Lancet which compared the relative increase of twinning
rates in the USA and UK.
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