Growth hormones in milk: myth/fact

This is the ninth of 16 student posts, guest-authored by Jaspreet Gill. 

It’s been over a decade since FDA approved use of artificial (recombinant) growth hormones in dairy cows. This topic remains controversial till this date. Not everyone is well educated on this subject and questions often come to people’s mind; what is this BST or growth hormone? Is there any link between milk artificial growth hormones and human biology??? Does it cause adverse effects on human health?

All milk contains small amounts of naturally-occurring hormones. Bovine somatotropin (BST) or bovine growth hormone (BHG) is a naturally-occurring hormone in cows that helps them produce milk. Amount of BST secreted in milk depends upon stage of lactation, parity, nutrition and herd environment. Growth hormone is a protein hormone produced in the pituitary gland of animals, including humans, and is essential for normal growth, development, and health maintenance.

Approximately 60 years ago, it was discovered that injecting cows with GH (growth hormone) extracted from cattle pituitary glands increased milk production. In the 1980s, it became technically possible and economically feasible to produce large quantities of bovine GH (bGH) using recombinant DNA processes

In 1993, FDA approved commercial use of synthetic recombinant Bovine somatotropin or growth hormone ( rbST or rbGH) in injection form to be used in cows to increase milk yield. It was marketed under name Posilac (company Monsanto). It has shown to increase milk yield in cows by 10-15 %. On other hand there are some reports showing that use of recombinant somatotropin/growth hormones increases the incidence of mastitis, lameness and some reproductive issues in the cows. Increased mastitis can be linked to high use of antibiotics for treatment and secretion of antibiotic residue in milk and meat products. In 1990, FDA evaluatedpharmaceutical company studies and concluded that the use of recombinant bovine growth hormone (rbGH) in dairy cattle presents no increased health risk to consumers and nutritional quality of milk and meat from rBST-treated cows is equivalent to that of milk and meat from untreated cows.

In 1990, an independent panel convened by the National Institute of Health (NIH evaluation) supported the FDA opinion that milk and meat from cows supplemented with rBST is safe for human consumption.

Despite of FDA and NIH review panel, approval of rBST (recombinant bovine growth hormone) provoked considerable debate among special interest groups, the media and in the scientific literature, as to whether milk from treated cows would cause adverse health effects.

Studies have shown that Human and bovine milk normally contain small amounts of growth hormone. After ingestion, growth hormone as any other protein in milk: it is digested into its constituent amino acids and di- and tripeptides. There is no data to suggest that BST present in milk can survive digestion or produce unique peptide fragments that might have biological effects. Even if BST is absorbed intact, the growth hormone receptors in the human do not recognize cow BST and, therefore, BST cannot produce effects in humans. Oral toxicity studies in rats show that rbGH is not orally active in rats which mean it cannot be absorbed into the system via digestion. Overall studies show recombinant growth hormone cannot be absorbed intact through intestine and even if small amounts get absorbed, there is no receptor for bovine growth hormones in Humans But gut of the very young infant is an immature organ that can absorb intact proteins in small amounts. Pasteurization inactivates/destroys most of the BST in milk. Most infant formulas receive intense heat treatment and there is no trace amount of BST found in infant formulas.

Other concern is insulin growth factor-1. Insulin-like growth factor (IGF) plays an important role in tissue growth and development. Several studies have shown association between circulating IGF and cancer risk. Increased levels of serum IGF-1 may be linked to increased risk of breast, colon, and prostate cancer.Studies have shown that Recombinant bovine growth hormone treatment produces an increase in insulin like growth factor IGF-1 in cow’s milk. The concentration of IGF-I, increases by 2 to 5 ng/ml in cows treated with rBST while untreated cow milk contains 3-10 ng/ml and human milk contains 1-3ng/ml.In human body, IGF-1 is produced naturally and present in saliva, biliary fluid, pancreatic juice ,secretions from intestinal mucosa, liver and extrahepatic tissues. Firstly, the amount of IGF-1 consumed daily from milk products is minute compared to natural endogenous production in Human body. Secondly, IGF-1 cannot be absorbed through stomach or intestine (won’t be able to escape proteolysis during intestinal passage) and even if small amounts were absorbed by the intestine and passed to circulation, it will contribute less than 0.06% of total daily IGF-1 production. IGF-1 is not denatured by pasteurization, so consumption of milk from rBST treated dairy cows will increase the daily oral intake of IGF-1, but serum levels will not be affected due to the denaturing effect within the stomach and intestine. It could be a concern in infants due to permeability of intestine but most infants are either breast fed or fed commercially prepared infant formulas which  contain no more than trace amounts of IGF-I . Intense high treatment used in manufacturing of infant formula inactivates approx 90 percent of the IGF-1.

In contrast, Posilac has been banned from use in CanadaAustraliaNew ZealandJapanIsraeland all European Union countries (currently numbering 27), from 2000 or earlier. In 1994 a European Union scientific commission European Union scientific commission stated that the use of rBST substantially increased health problems with cows, including foot problems, mastitis and injection site reactions, impinged on the welfare of the animals and caused reproductive disorders. The report concluded that, on the basis of the health and welfare of the animals, rBST should not be used.

In 1998, Canada established an expert panel to examine the human safety issues pertinent to the use of RBST in dairy cattle.Canadian expert panel findings were that that there was no increase in total bST concentration is observed in milk from rbST-treated cows and therefore no human risk. Secondly that RbST increases the production of IGF-1 concentrations in recipient animals and IGF-1 concentrations are increased in food products from rbST-treated cattle. in recipient animals. However, there is no biologically basis on which to conclude that rbST-associated changes in human exposure to IGF-1 will lead to any immune response, change in neonatal intestinal growth and development, or cancer risk in recipients of milk or food products from treated cattle.  Canadaprohibited the sale of rBST in 1999stating that drug presents a threat to animal health.

The FDA does not require special labels for milk or like products produced from cows treated with rbST. According to FDA all milk contains BST(Bovine somatropin or Bovine growth hormone) so milk or milk products cannot labeled as rbST or rbGH free because it will be misleading to the consumers. Some people prefer to consume milk and milk products that were not produced with rbST. To meet their needs, some processors donot use it and label their milk and milk products as rbST free. However consumer can feel confident that all milk produced and sold in Unites states-with or without rbST-contains the same nutrients and safe for human consumption.


Collier RJ, Miller MA, Hildebrandt JR, Torkelson AR et al. Factors affecting insulin-like growth factor-1 concentration in bovine milk. J Dairy Sci 1991; 74 :2905– 2911

Daxenberger ABreier BHSauerwein H. Increased milk levels of insulin-like growth factor 1 (IGF-1) for the identification of bovine somatotropin (bST) treated cows. Analyst. 1998; Dec; 123(12):2429-35.

Groenewegen, P.P, McBride, B.W.,Burton, J.H., and T.H. Elsasser. Bioactivity of milk from bST-treated cows.  J. Nutr 1990; 120: 514-520.

Juskevich JCGuyer CG. Bovine growth hormone: human food safety evaluation. Science 1990; 249(4971): 875- 84

Parodi PW. Dairy product consumption and the risk of breast cancer. J Am Coll Nutr. 2005; Dec;24(6 Suppl):556S-68S.

Weroha SJHaluska P. The insulin-like growth factor system in cancer. Endocrinol Metab Clin North Am. 2012; 41(2):335-50.

Report on the Food and Drug Administration’s Review of the Safety of Recombinant Bovine Somatotropin. 1999. Retrieved 2009-05-02.

National Institutes of Health (US). Office for Medical Applications of Research. NIH State of the Science Statements [Internet]. Bethesda (MD): National Institutes of Health (US); 1983-2002. Bovine Somatotropin.

The Scientific Committee on Animal Health and Animal Welfare, European Union.. Report on Animal Welfare Aspects of the Use of Bovine Somatotrophin. 1999-03-10.

Health Canada. Health Canada rejects bovine growth hormone in Canada.. 1999-01-14.

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