Background

Recombinant bovine growth hormone (rBGH) is a synthetic hormone that is marketed to dairy farmers to increase milk production. The use of rBGH in the United States was approved by the Food and Drug Administration in 1993, but has been banned in the European Union and Canada since 1999. This document summarizes available information about the product and its potential effects on health.

What is synthetic (recombinant) bovine growth hormone (rBGH)?

The human form of growth hormone, also called somatotropin, is produced by the pituitary gland, and promotes growth and cell replication. Bovine somatotropin is the naturally occurring form of this hormone in cattle. Synthetic or recombinant somatotropin (rBGH or rBST) refers to bovine growth hormone that is manufactured in a laboratory using genetic technology. Some rBGH products on the market differ chemically from a cow’s naturally occurring somatotropin by one amino acid (called methionine). Both the natural and synthetic forms of the hormone stimulate milk production by increasing circulating levels of another hormone known as insulin-like growth factor (IGF-1).

What are the health concerns in humans?

Concerns about possible adverse health effects on humans from milk produced using rBGH have focused on 2 questions:

1) Is the absorption of bovine insulin-like growth factor (IGF-1) from milk sufficient to increase circulating blood levels of IGF-1 in consumers?

and

2) Does the increased use of antibiotics to treat rBGH-induced mastitis in cows increase exposure to antibiotic resistant bacteria?

The first question has been addressed in past scientific reviews (see below). The second question remains a concern, and we do not yet know the answer. It has not been fully examined in humans.

Is IGF-1 from rBGH treated milk absorbed by people who drink it?

Some studies have shown that adults who drink milk have approximately 10% higher levels of insulin-like growth factor (IGF-1) in the blood than those who drink little or no milk. But this same observation has been reported in people who drink soymilk. This suggests that this finding is not specific to cow milk, and may be caused by protein, minerals, or some other factor unrelated to rBGH. There have been no direct comparisons of IGF-1 levels in people who drink ordinary milk vs. milk stimulated by rBGH.

Substantial evidence indicates that IGF levels at the high end of the normal range may influence the development of certain tumors. Normal and cancerous cells from a variety of tissues have IGF receptors on their surface. And high concentrations of IGF are known to stimulate growth. Several prospective studies found a relationship between circulating levels of IGF-1 and the development of prostate, breast, colorectal, and other cancers. But later studies have failed to confirm these reports or have found weaker relationships.

Still, there is no evidence that drinking milk, produced with or without rBGH treatment, increases circulating IGF levels into the range of concern. So it is unclear whether drinking milk treated with rBGH has any effect on cancer risk.

Scientific reviews

In the early 1990s, the FDA and other organizations looked at 3 questions regarding IGF-1 exposure from rBGH-treated milk. These were:

• How much higher is the insulin-like growth factor (IGF-1) concentration in cow’s milk produced with rBGH, compared to that in untreated milk?

• How much of the additional IGF-1 in milk do consumers absorb in an intact, pharmacologically active form?

• How does the amount of absorbed IGF-1 compare with normal endogenous production of IGF-1 by humans?

The available evidence can be summarized as follows:

• Neither natural nor synthetic bovine growth hormone has been found to affect human growth hormone receptors.

• IGF-1 concentrations are slightly higher (to variable degrees, depending on the study) in milk from cows treated with rBGH than in untreated milk. This variability is presumed to be much less than the normal variation of IGF-1 in cow’s milk attributable to parity and stage of lactation, but more investigation is needed.

• IGF-1 in milk is not denatured (inactivated) by pasteurization. The extent to which intact, pharmacologically active IGF-1 is absorbed through the human gastrointestinal tract remains uncertain.

• One study estimated that the additional amount of IGF-1 that might be absorbed by humans, assuming no degradation and complete absorption, represents 0.8% of normal gastrointestinal secretion and 0.09% of the daily production of IGF-1 in adults.

• Before approving the use of rBGH in 1993, the FDA calculated a worst case scenario that assumed that an infant drinks 1.5 liters (1 liter is approximately 1 quart) of milk daily with complete absorption of intact IGF-1 protein, and the maximum increase in IGF-1. Under these conditions, the rBGH treated milk would contribute far less than 1% of the infant's normal daily production of IGF-1.

At least 8 other national and international review committees have evaluated the evidence concerning potential adverse health effects of rBGH on humans and dairy cows. These reviews (and the most recent year they convened) are listed below. Several of these reports document adverse effects on cows, including higher rates of mastitis, foot problems, and injection site reactions.

• The Joint FAO/WHO Expert Committee on food additives (1999)
• Health Canada (1999)
• The Royal College of Physicians and Surgeons of Canada (1998/9)
• Canada Veterinarian Association (1998/9)
• The Commission of the European Communities (1988/9)
• The US National Institutes of Health (1990)
• American Medical Association (1991)
• Health Care Without Harm (2007)

Usage and regulatory status

Although the use of rBGH is still approved in the United States, demand for the product has decreased in recent years. A USDA survey conducted in October, 2007 found that less than 1 in 5 (17%) cows were being injected with rBGH.

Summary

The available evidence documents adverse health effects from rBGH on cows. The evidence for potential harm to humans is inconclusive. To date, there is no evidence that drinking milk produced using rBGH adds substantively to circulating IGF-1 levels in humans or to the risk of developing cancer. The increased use of antibiotics to treat rBGH-induced mastitis does promote the development of antibiotic resistant bacteria, but the extent to which these are transmitted to humans is unclear. The president of the American Medical Association has recommended that hospitals serve milk produced without the use of rBGH.

The American Cancer Society (ACS) has no formal position regarding rBGH. Together with its advocacy affiliate, the ACS Cancer Action Network (ACS CAN), the Society supports open, fair and transparent regulatory oversight of products containing rBGH. The ACS also encourages continued and expanded scientific research and independent, credible assessment of potential relationships between the use of this substance in cows and human cancer risk. We support regulatory standards based on rigorous scientific evidence to minimize exposure to carcinogens, and we encourage the FDA to give the public information regarding known and suspected causes of cancer in the food system. The need for an effective FDA in ensuring the safety of our food supply, medicines, and consumer products has never been greater.

References

Allen NE, Appleby PN, Davey GK, Kaaks R, Rinaldi S, Key TJ. The associations of diet with serum insulin-like growth factor I and its main binding proteins in 292 women meat-eaters, vegetarians, and vegans. Cancer Epidemiol Biomarkers Prev. 2002;11:1441-1448.

Allen NE, Key TJ, Appleby PN, et al. Serum insulin-like growth factor (IGF)-I and IGF-binding protein-3 concentrations and prostate cancer risk: Results from the European Prospective Investigation into Cancer and Nutrition. Cancer Epidemiol Biomarkers Prev. 2007;16:1121-1127.

Furstenberger G, Senn HJ. Insulin-like growth factors and cancer. Lancet Oncology. 2002;3:298-302.

Giovannucci E. Nutrition, insulin, insulin-like growth factors and cancer. Hormone & Metabolic Research. 2003;35:694-704.

Giovannucci E, Pollak M, Liu Y, et al. Nutritional predictors of insulin-like growth factor I and their relationships to cancer in men. Cancer Epidemiol Biomarkers Prev. 2003;12:84-89.

Hankinson SE, Schernhammer ES. Insulin-like growth factor and breast cancer risk: Evidence from observational studies. Breast Dis. 2003;17:27-40.

Health Canada: Report of the Canadian Veterinary Medical Association Expert Panel on rbST. 1998 Royal College of Physicians and Surgeons of Canada. Accessed at http://www.hc-sc.gc.ca/dhp-mps/vet/issues-enjeux/rbst-stbr/rep_rcpsc-rap_crmcc_final-a-eng.php on February 17, 2009.

Health Canada: Recombinant Bovine Somatotropin. Accessed at http://www.hc-sc.gc.ca/dhp-mps/vet/issues-enjeux/rbst-stbr/index-eng.php on February 17, 2009.

Holmes MD, Pollak MN, Willett WC, Hankinson SE. Dietary correlates of plasma insulin-like growth factor I and insulin-like growth factor binding protein 3 concentrations. Cancer Epidemiol Biomarkers Prev. 2002;11:852-861.

Max JB, Limburg PJ, Ogunseitan A, et al. IGF-I, IGFBP-3, and IGF-I/IGFBP-3 ratio: No association with incident colorectal cancer in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study. Cancer Epidemiol Biomarkers Prev. 2008;17:1832-1834.

Pollak M. Insulin and insulin-like growth factor signalling in neoplasia. Nat Rev Cancer. 2008;8:915-928.

Renehan AG, Zwahlen M, Minder C, O'Dwyer ST, Shalet SM, Egger M. Insulin-like growth factor (IGF)-I, IGF binding protein-3, and cancer risk: Systematic review and meta-regression analysis. Lancet. 2004;363:1346-1353.

Rinaldi S, Peeters PH, Berrino F, et al. IGF-I, IGFBP-3 and breast cancer risk in women: The European Prospective Investigation into Cancer and Nutrition (EPIC). Endocr Relat Cancer. 2006;13:593-615.

Schernhammer ES, Holly JM, Hunter DJ, Pollak MN, Hankinson SE. Insulin-like growth factor-I, its binding proteins (IGFBP-1 and IGFBP-3), and growth hormone and breast cancer risk in The Nurses Health Study II. Endocr Relat Cancer. 2006;13:583-592.

U.S. Food and Drug Administration. Report on the Food and Drug Administration's Review of the Safety of Recombinant Bovine Somatotropin. Accessed at http://www.fda.gov/cvm/RBRPTFNL.htm on February 17, 2009.

World Health Organization. Joint FAO/WHO Expert Committee on Food Additives (JECFA). Toxicological evaluation of certain veterinary drug residues in food. Monograph 41. Geneva, February 1998. Accessed at http://www.inchem.org/documents/jecfa/jecmono/v041je11.htm on February 17, 2009.

Last Medical Review: 02/17/2009
Last Revised: 02/17/2009