Bovine Growth Hormone (rBGH/rBST)
CATEGORY: Endocrine disruptor
USED IN: Dairy products
Despite opposition from physicians, scientists and consumer advocacy groups, the Food and Drug Administration in 1993 approved Monsanto’s genetically engineered hormone product, recombinant bovine growth hormone (rBGH), for injection in dairy cows to increase milk production (Eaton, 2004). This hormone quickly found its way (without labeling) into the U.S. milk supply and from there into ice cream, buttermilk, cheese, yogurt and other dairy products. Since its introduction, rBGH (subsequently renamed recombinant bovine somatotrophin, rBST) has proven controversial because of its potentially carcinogenic effects.
Drinking any type of cow’s milk noticeably raises body levels of insulin-like growth factor 1 (IGF-1), a naturally occurring hormone in both cows and humans. Injecting cows with rBST leads to an increase in IGF-1 levels in milk (Daxenbeger, 1998), although a recent study has suggested that the increased milk output by treated animals may dilute the excess production of hormone (Collier, 2008). The content of IGF-1 in dairy milk is not altered by pasteurization (Collier, 1991).
Although the data are complex, with studies reaching different conclusions, several epidemiological studies have indicated a relationship between dairy consumption and breast cancer risk in pre-menopausal women (Outwater, 1997). Elevated levels of IGF-1, in particular, have been associated with increased risk of breast cancer (Hankinson, 1998).
Proponents of rBST argue that IGF-1 is harmless because it occurs naturally in humans, is contained in human saliva and is broken down during digestion. However, animal evidence indicates that digestion does not break down IGF-1 in milk because casein, the principal protein in cow's milk, protects IGF-1 from the action of digestive enzymes (Xian, 1995).
