Human Health Issues of Bovine Somatotropin

Recombinant BST is indistinguishable from natural BST, as it contains the same amino acids in the identical sequence, with the same shape and properties. BST occurs naturally in cows’ milk and meat in very small quantities. Supplemental administration of BST to cows does not increase the amount of BST found in their milk. Because BST and human somatotropin are very different in structure, BST is not active in humans, even if it is injected into the bloodstream. BST does not change the composition of milk in any significant way.

Furthermore, BST would not be a human food safety concern because it is digested in the stomach just like any other protein. For these reasons, some scientists say BST itself poses no human health risk. BST regulates another protein hormone found in milk, insulin-like growth factor I (IGF-I). IGF-I is a normal component in the human gastrointestinal tract, where it occurs in much greater amounts than it does in cows’ milk. Normal concentration of IGF-I in the blood of adults and children can be more than 100 times greater than that found in cow’s milk, which means that the amount of IGF-I in milk is small compared to what the human body produces. Both sides agree that levels of IGF-I are higher in milk produced from BST-treated cows than from non-treated cows, however it is the interpretation of this that differs.

Bovine IGF-I and human IGF-I are identical in structure, a fact that BST opponents believe poses serious risks for human health. They cite studies showing that women with small increases of IGF-I levels in their blood are up to seven times more likely to develop breast cancer than women with lower levels, and that high levels of IGF-I are also a risk factor for prostate and colon cancer. Proponents of BST claim that higher levels of IGF-I in milk are not a safety risk since it is a protein and therefore is digested and rendered harmless just like all other dietary proteins.

These proponents also point out that the person who first published the link between BST and cancer did so in a non-research journal of which he is on the editorial board, and that he is an activist of many years standing in the crusade against use of any chemicals in food. In spite of proponents claiming that IGF-I is fully digested, opponents claim that in the presence of casein, a normal milk protein, IGF-I resists digestion. Opponents allege that contrary to what FDA and Monsanto claim, long-term toxicology studies addressing such possibilities as sterility, infertility, birth defects, and cancer have not been performed for BST.