Fat, however, may vary somewhat in earlier stages of supplementation. Normal levels of bST in milk, about 10 ppb, are not significantly affected by administration of the hormone to the cow. The modest rise of IGF-I concentration is well within normal variation and at a level below its concentration in human milk. Early clinical researchers studying bST were hopeful of its usefulness in treating human dwarfism. However, though the protein could be safely injected into humans, it was not biologically active.
Growth hormones are species-specific.
Since it is a protein hormone, it is digested by humans into peptides and amino acids like any other protein. In fact, when presented to a cow orally, bST is not active. The cow's digestive system simply recognizes it as dietary protein. Though the human safety of naturally-occurring bST had been established in the 1950's, many more extensive studies were required by FDA prior to the approval for marketing milk from test cows in 1985. Then, prior to approving the marketing of recombinant bST in the U.S., many other issues, such as animal health and labeling, had to be resolved.