Allegations that bST increases risk of breast cancer in women

Some consumer activists have made this claim based on the relationship between somatotropin and a compound known as insulin-like growth factor (IGF-I), and an association between IGF-I and breast tumor formation. Somatotropin stimulates local production of IGF-I in tissues to mediate some of its biological effects. IGF-I is a protein required for normal growth and health maintenance.

Recombinant bGH treatment produces a slight increase in the concentration of IGF-I in cow's milk. If it were injected, IGF-I could be active in humans. However, oral toxicity studies have shown that bovine IGF-I lacks oral activity in rats. Additionally, the concentration of IGF-I in milk of rbGH-treated cows is within the normal physiological range found in human breast milk. IGF-I is not destroyed by pasteurization of milk, but it is denatured by the heat treatment used in producing infant formula. On the basis of estimates of the amount of protein absorbed intact in humans and the concentration of IGF-I in cow's milk during rbGH treatment, biologically significant levels of intact IGF-I are unlikely to be absorbed.

A search of the medical literature has found no epidemiologic studies finding an association between breast cancer risk and consumption of milk from bST-treated cows (July, 1997).


Hammond-B-G. Collier-R-J. Miller-M-A. McGrath-M. Hartzell-D-L. Kotts-C. Vandaele-W. Food safety and pharmacokinetic studies which support a zero (0) meat and milk withdrawal time for use of sometribove in dairy cows. Ann-Rech-Vet. 1990. 21 Suppl 1. P 107S-120S.

Juskevich-J-C. Guyer-C-G.Bovine growth hormone: human food safety evaluation [see comments] Science. 1990 Aug 24. 249(4971). P 875-84.

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Prepared Summer 1997 by Bernadene Magnuson, Ph.D.
University of Idaho, Dept. of Food Science and Toxicology - EXTOXNET FAQ Team.