Recombinant somatotropin, rBST (previously called
bovine growth hormone, rBGH), is a genetically engineered hormone injected
into dairy cows to increase milk production. Milk from rBST-treated cows
is used in dairy products including ice cream, butter, cheese and
yogurt.
The United States does not require companies to label the use of rBST
in their products, although it was banned in the European Union in
1990. The use of rBST in dairy cows has been shown to increase the
concentrations of IGF-1, a protein naturally found in milk.
Though research is mixed on the extent to which dairy consumption is linked to increased cancer risk, higher blood levels of IGF-1 have been linked to increased risk for pre-menopausal breast cancer.
