The Consumer Education Project of Milk SA

Does the milk we buy contain hormones?

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All mammal milk, including human milk, contains hormones.

Let’s consider some hormones in cow’s milk:

  • Growth hormone from a cow has no biological activity in humans. Bovine growth hormone (bGH; also called bovine somatotropin, bST) is a so-called peptide hormone. This means that it is made from amino acids, just like any other protein we eat and digest. There is no scientific evidence to indicate that growth hormone from milk should be able to survive our digestion or that fragments from this digestion has any biological activity. The amount of growth hormone in cow’s milk is very low (approximately 0.001 g/L, and close to 90% of it is destroyed during the heat treatment milk is subjected to during processing.
  • Recombinant bovine somatotropin (r-bST) is a synthetic hormone supplement that increases milk production. This makes our natural resources go further by reducing the use of water, land emissions and feed for each litre of milk produced. Because rbST works with the cow’s natural means of producing milk, milk from cows that are given the supplement is not any different from that of cows that are not given the supplement.

The use of rBST is legal in South Africa, as it is not considered a food safety risk. This is in line with the view in many other countries..

  • IGF-1 (insulin-like growth factor 1) is also a peptide hormone, just like growth hormone. However, the two hormones are not the same. IGF-1 is produced by the liver in response to the pituitary gland’s production of growth hormone. The concentrations of IGF-1 in cow’s milk, which is similar to the concentration of IGF-1 in mother’s milk, is much lower than the concentrations of IGF-1 in the digestive fluids in our gastrointestinal tracts. The amount of IGF-1 in cow’s milk is simply too small to have any effect.
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