Myth-Busting: The Facts Versus the Myths Regarding rbST

rbST has been proven safe by several regulatory authorities, together with their scientific assessment bodies. However, misconceptions still exist about whether milk produced by cows supplemented with rbST is safe for human consumption. The following information debunks these myths.

MYTH: rbST is unsafe for humans.
FACT: rbST use in dairy cows poses no human health risk.

Extensive human studies have established that humans are biologically unaffected by rbST. It is noted that even if rbST is absorbed intact, the growth hormone receptors in the human do not recognize rbST and therefore, rbST cannot produce effects in humans.1

MYTH: rbST is a hormone, and therefore milk from rbST-supplemented cows is harmful to the human body.
FACT: There are two types of hormones: steroids and proteins. rbST is a protein hormone, which means that it is inactive when taken orally, just like insulin, because it is broken down in the digestive system.2

rbST is not active in the human body.

MYTH: rbST is a steroid hormone given to cows.
FACT: rbST is not a steroid hormone, it is a protein. Because it is a protein it is digested like any other protein when consumed.
MYTH: Milk from rbST-supplemented cows contains hormones while organic milk is free from hormones.
FACT: All milk contains hormones, and the levels of those hormones are not biologically different between organic, rbST-free, and regular milk.

bST, from which rbST is derived, occurs naturally in milk at minuscule levels, normally less than 1 part per billion. That’s equivalent to one drop in 22,000 gallons of milk. This amount does not increase in the milk of rbST-supplemented cows.3, 4

MYTH: rbST-supplemented milk contains antibiotics.
FACT: All milk, regardless of production practice, is tested and milk determined to contain antibiotics is discarded.

Federal and state monitoring programs require all milk to be tested to ensure the safety and wholesomeness of milk. Milk is one of the most monitored products in the American food supply, and every shipment of milk is tested and thoroughly inspected several times during the journey from the farm to the grocery store. In all instances, the milk supply meets stringent government-established safety standards.

MYTH: rbST use causes breast cancer in humans.
FACT: Drinking milk does not increase breast cancer risk, regardless of whether the milk is organic, rbST-free or regular. In fact, milk contains many elements that have the potential to protect against breast cancer, such as rumenic, vaccenic, butyric and branched chain fatty acids, whey protein, calcium and vitamin D.5

rbST was approved by the FDA in 1993. There has actually been a decline in the rate of breast cancer during the time period that rbST has been approved for commercial use.5

MYTH: rbST greatly increases the amount of insulin-like growth factor (IGF-1), a polypeptide protein hormone found in all milk, which is said to cause cancer.
FACT: IGF-1 (insulin-like growth factor-1) is present in all milk at slightly varying levels. Even if the content of IGF-1 in rbST-supplemented milk is increased twofold, the amount of IGF-1 contained in the daily recommended amount of milk would be very, very low — less than 1% of the amount that is present in intestinal secretions and less than one ten-thousandth of that produced by the human body.6, 7 By comparison, the daily IGF-1 level in human saliva and other digestive secretions is equal to the amount of IGF-1 in 270 glasses of cows’ milk.8 Therefore, there is no evidence that this amount of IGF-1 would pose a health hazard.

Additionally, IGF-1 has never been shown to transform a healthy cell into a cancer cell. Digestive secretions, such as saliva, contain IGF-1 which has never been shown to cause intestinal cell transformation. 9, 10, 11, 12, 13, 14, 15, 16

MYTH: Milk from rbST-supplemented cows contains IGF-1.
FACT: IGF-1 is present in all milk regardless of the farm production practice — including from those cows that are rbST-supplemented, rbST-free and organic. Furthermore, IGF-1 levels in milk from rbST-supplemented cows are within the normal range of levels found in the milk of non-rbST-supplemented cows.3
MYTH: rbST use causes the onset of early puberty in girls.
FACT: Many factors influence the age of puberty in boys and girls,17, 18 but specific foods or non-nutrient substances in foods, such as hormones, are NOT associated with changes in the age of puberty.

Since all milk — regular, organic or rbST-free — has the same composition, there are no differences in the dairy products from rbST-supplemented cows that could affect the age at which puberty begins.

The increasing weight and height of boys and girls over the past century due to improved health and nutrition has been associated with earlier onset of puberty. While, malnutrition, high altitude, chronic infections, and chronic illnesses, such as inflammatory bowel disease and cystic fibrosis, in which nutritional status and weight gain are impacted, have all been associated with a delay in the onset.

MYTH: Milk from rbST-supplemented cows is not as “good” — not as nutritious or tasty — as milk from non-supplemented cows.
FACT: Milk produced by cows supplemented with rbST is indistinguishable from milk produced by other cows — all milk is the same. Regardless of the farm production practice, milk from cows that are rbST-supplemented, rbST-free, and organic is compositionally similar.19

The nutritional and taste characteristics remain the same for all milk as it comes from the cow.

MYTH: rbST use is not “green.”
FACT: Improving milk productivity improves environmental sustainability. Six cows supplemented with rbST will produce the same amount of milk as 7 non-supplemented cows (image)Link opens in a new window. Therefore the farmer needs less feed, water, and resources to make the same amount of milk.20 Increasing productivity is the key element in environment stewardship.
MYTH: rbST increases mastitis incidence in cows and may cause antibiotic resistance.
FACT: The risk that cows receiving rbST may experience mastitis (infection in the udder) is much smaller than the risk from the environment and milking procedures and can be managed like all other risk factors on the dairy.21

There have been post-approval publication of studies involving hundreds of commercial dairy herds and publication of large experimental data summaries. Variables have included mastitis incidence, cultures for mastitis organisms, somatic cell counts, culling rates and veterinary costs. These studies found no evidence that commercial use of rbST represented a significant concern for mastitis or antibiotics.22

Scientific evidence does not support a widespread, emerging resistance among mastitis-causing bacteria to antibitotics.23

Milk pasteurization further helps ensure milk safety.

MYTH: rbST is harmful to the welfare of animals.
FACT: rbST is not harmful to the welfare of animals.

rbST does not alter the stayability (the length of time a cow stays in the herd) and herd-life of animals. A field study of 340 herds, more than 80,000 cows and 200,000 lactations reported on the positive well-being of the animals, through variables such as cow performance and average age, which are the best indications of well-being.24

The Posilac product label (pdf)Link opens in a new window contains complete use information, including cautions and warnings. Always read, understand, and follow the label and use directions.

To increase production of marketable milk in healthy lactating dairy cows, supplement lactating dairy cows every 14 days beginning at 57–70 days in milk until the end of lactation.

1 NIH Technology Assessment Conference Statement, Dec 5–7, 1990.

2 bST Fact Sheet. Cornell University. 1995. Last accessed on March 1, 2009.

3 Daughaday WH et al. Bovine Somatotropin Supplementation of Dairy Cows. JAMA, Vol 264:1003, Aug 22–24, 1990.

4 Schams D. Somatotropin and Related Peptides in Milk. Use of Somatotropin in Livestock Production. 1989. pp. 192–200.

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

6 Guler HP et al. Insulin-like growth factors I and II in healthy man. Estimations of half lives and production rates. Acta Endocrinol (Copenh). 1989 Dec;121(6):753–8.

7, 8 FAO/WHO Expert Committee on Food Additives. The fiftieth meeting of the Joint FAO/WHO Expert Committee on Food Additives (JECFA). Toxicological evaluation of certain veterinary drug residues in food; and summary and conclusions. World Health.

9 Blum JW and Baumrucker CR. Colostral and milk insulin-like growth factors and related substances: mammary gland and neonatal (intestinal and systemic) targets. Domest Anim Endocrinol. 2002 Jul;23(1–2):101–10.

10 CVM Update: FDA Responds to Citizen Petition on BST. Food and Drug Administration (FDA) Center for Veterinary Medicine (CVM). April 21, 2000. Last accessed June 22, 2009.

11 Clark RG. Recombinant human insulin-like growth factor-I (IGF-1): risks and benefits of normalizing blood IGF-1 concentrations. Horm Res. 2004;62 suppl 1:93–100.

12 Ryan J et al. Salivary insulin-like growth factor-I originates from local synthesis. J Endocrinol. 1992 Oct;135(1):85–90.

13 Werner H and Katz J. The emerging role of insulin-like growth factors in oral biology. J Dent Res. 2004 Nov;83(11):832–6.

14 Burrin DG. Is milk-borne insulin-like growth factor-I essential for neonatal development. J Nutr. 1997 May;127(5 Suppl):975S–979S.

15 Liu X et al. Enteral nutrients potentiate the intestinotrophic action of glucagon-like peptide-2 in association with increased insulin-like growth factor-I responses in rats. Am J Physiol Regul Integr Comp Physiol. 2008 Dec;295(6):R1794-802.

16 Booth C et al. Growth factor regulation of proliferation in primary cultures of small intestinal epithelium. In Vitro Cell Dev Biol Anim. 1995 Mar;31(3):234–43.

17 Chumlea WC et al. Age at menarche and racial comparisons in US girls. Pediatrics. 2003 Jan;111(1):110–3.

18 Steingraber S. The falling age of puberty in US girls: what we know, what we need to know. Breast Cancer Fund. August 2007. Last accessed June 22, 2009.

19 Vicini et al. Survey of Retail Milk Composition as Affected by Label Claims Regarding Farm Management Practice. J Am Diet Assoc. 2008 Jul: 108(7):1198–203.

20 Capper JL et al. The environmental impact of recombinant bovine somatotropin (rbST) use in dairy production. Proceedings of the National Academy of Sciences. July 15, 2008; Vol. 105, no. 28.

21 Freedom of information summary: Posilac. 1993. Last accessed on March 1, 2009.

22 Collier RJ et al. Effects of sustained release bovine somatotropin (sometribove) on animal health in commercial dairy herds. J Dairy Sci. 2001 May; 84(5):1098–108.

23 Erskine R et al. Bovine Mastitis Pathogens and Trends in Resistance to Antibacterial Drugs, NMC Annual Meeting Proceedings, National Mastitis Council Research Committee Report. 2004.

24 Bauman DE. Production responses to bovine somatotropin in northeast dairy herds. J Dairy Sci. 1999 Dec;82(12):2564–73.

Recent Research

An independent assessment on rbST titled “Recombinant Bovine Somatotropin (rbST): A Safety Assessment,” was released in July 2009.