rbGH stands for "recombinant bovine growth hormone," and it is estimated to be used in the raising of approximately 15-20% of U.S. dairy cows. You'll also see this hormone called rbST (recombinant bovine somatotropin). Originally developed by Monsanto and now produced by Elanco (a company which acquired rights to the synthetic hormone from Monsanto in 2008), rbGH is sold under the brand name Posilac (TM) and it is one of the largest dairy animal pharmaceutical products sold in the U.S. While still used in the production of non-organic dairy products, use of rbGH and rbST is not allowed in the production of organic products.
Use of rbGH in dairy cows in the U.S. began in the mid-1990's as a way of increasing milk production. Even though the U.S. Food and Drug Administration (FDA) continues to allow for use of rbGH in the raising of dairy cattle, there has been widespread rejection of this practice outside of the U.S., including countries like Canada, Australia, New Zealand, Japan, and all countries belonging to the European Union (27 countries, including the United Kingdom, France, Spain, Italy, Germany, Greece, Hungary, Poland, Norway, Sweden and Denmark). In addition, many large retailers and manufacturers in the U.S. have rejected use of rbGH in their products.
From a physiological perspective, rbGH is part of a complicated network of hormones and hormone-like substances that are required for growth and proper differentiation of cells. An especially important part of this network is a polypeptide (small protein-like molecule) called insulin-like growth factor 1, or IGF-1. In humans, elevated blood levels of IGF-1 are associated with increased risk of certain cancers, especially breast cancer in women and prostate cancer in men. Cows injected with rbGH would, of course, be expected to have elevated amounts of rbGH in their bodies. In addition, however, cows injected with rbGH would be expected to have higher levels of IGF-1 as well. A question raised by many scientists is whether humans regularly consuming milk from rbGH-injected dairy cows are at increased risk for IGF-1 exposure and IGF-1 associated cancers. We have not seen any large-scale human study that has determined regular consumption of milk from rbGH-injected cows to be a risk factor for cancer. In fact, we've found indexed-journal reviews in this area that report no evidence for this association. Still, the connection between excessive exposure to growth hormone, insulin-like growth factor 1, and increased cancer risk makes logical sense to us, and it's difficult for us to dismiss the rejection of this cow-raising practice by so many countries. It's a practice that we would like to see prohibited in the U.S., and it's also a practice whose outcome can be avoided through the purchase of certified organic milk (and other certified organic dairy products). Not only is the use of rbGH prohibited in the production of organic milk and milk products, but also prohibited is the use of many other potentially toxic substances.
Kaaks, R. (2004). "Nutrition, Insulin, IGF-1 Metabolism and Cancer Risk: a Summary of Epidemiological Evidence." Novartis Found Symp 262: 247-60; discussion 260-68.
Lonning PE and Helle SI. (2004). IGF-1 and Breast Cancer. Novartis Found Symp 262 (2004): 205-12; discussion 212-4, 265-268.
Parodi PW. (2005). Dairy Product Consumption and the Risk of Breast Cancer. J Am Coll Nutr December 2005 vol. 24 no. suppl 6 556S-568S.
Roberts CT Jr. IGF-1 and Prostate Cancer. Novartis Found Symp 262 (2004): 193-9; discussion 199-204, 265-8.