Hormones: What’s in your milk? Back »

Hormones are normal constituents of milk that are a continuous topic of debate. Hormones are usually peptides or steroids produced in one tissue, transported by blood, to cause another target tissue or organ to modify growth, metabolism, or reproduction. Hormones are essential for growth in humans and animals and can be transferred in small amounts from the blood into milk. Table 1 below defines milk and the three types of milk that can be commercially available to purchase depending on your location.

Table 1. Milk and milk types

Milk Mammary gland secretion of mammals used to nourish their young.
Organic Produced only by certified organic farms (not the same as raw).
Raw Directly from the farm; not pasteurized (not the same as organic).
Pasteurized Milk is transported refrigerated to the processing plant, heat-treated at 160º F for 15 seconds to kill pathogens, and then homogenized.


Research has found milk contains 18 hormones in significant amounts that can be measured (Table 2). Traces of female and male hormones in milk are at six and five times lower concentrations when compared to these same hormones found in eggs. Female hormones in milk are: alpha and beta estradiol, and estrone; male hormones are: alpha and beta testosterone, dehydroepiandrosterone, and androstenedione (Courant et al. 2011).

Table 2. Hormones present in all milk types*

Production site Hormone
Gonads estrogens, progesterone, androgens
Adrenal gland corticosterone, cortisol, androstenedione
Pituitary prolactine, growth hormone (BST)
Hypothalamus gonadotropin releasing hormone, luteinizing hormone, thyrotropin releasing hormone, somatostatin
Other locations parathyroid hormone related protein, insulin, calcitonin, bombesin, erythropoietin, melatonin

*Traces are present in similar concentrations in organic, raw, and pasteurized milk. Jouan et al. 2006.

The effect of pasteurization on the hormones present in milk is variable. Organic, raw and pasteurized milk have similar concentrations of gonadal hormones (androgens, estrogens, and progesterone). Pasteurized, organic, and raw milk have the same concentration of parathyroid hormone-related protein. Pasteurization will not destroy insulin-like growth factor-I, a normal component of all types of milk. Pasteurization inactivates 90% of the growth hormone found in milk.

Growth hormone

The synthetic form or recombinant growth hormone (rBST), which is the same form as the natural growth hormone (BST), is the one hormone the public is mostly concerned about. It is produced in the laboratory and injected into lactating dairy cows. Growth hormone enhances milk production without affecting the total growth hormone content in milk. This same effect has also been proven in humans. In a 2011 experiment conducted by the Academy of Breastfeeding Medicine, breast-feeding women were injected daily and for 7 days with 0.5 international units of growth hormone every 10 pounds of body weight. No differences were detected above normal growth hormone (GH) concentrations found in breast milk, in spite of the additional dosage. It was concluded that injected GH does not increase milk GH concentrations and had no adverse effects on breastfed infants or their mothers. As in other species, human breast milk output was increased 19 to 36% after the administration of GH.

Raw milk contains all the same active hormones, as mentioned above, including growth hormone. However, the biologically active form of growth hormone present in raw milk or even the remaining 10% in pasteurized milk is of no consequence to humans. Growth hormone is species specific, so the growth hormone in cow’s milk is only active in the cow and then, only if injected. The normal digestion process will destroy any remaining growth hormone, by breaking it down into the individual amino acids, like any protein consumed.

Should milk be labeled hormone free or growth hormone free? As pointed out, milk that is commercially available as organic, raw, or pasteurized, has traces of natural hormones, including growth hormone. In the best case, milk can only be stated as coming from cows not receiving recombinant growth hormone. At the present time, there are no assays that can differentiate between natural growth hormone and recombinant growth hormone, precisely because they are the same hormone.


  • Academy of Breastfeeding Medicine Protocol Committee. ABM clinical protocol #9: use of galactogogues in initiating or augmenting the rate of maternal milk secretion (First revision January 2011). Breastfeed Med. 2011;6:41-9. PMID: 21332371
  • Courant, F., J.-P. Antignac, D. Maume, F. Monteau, F. Andre and B. Le Bizec. 2007. Determination of naturally occurring oestrogens and androgens in retail samples of milk and eggs. Journal: Food Additives & ContaminantsVolume 24, Issue 12: pages 1358-1366
  • Jouan, P.N., Y. Pouliot, S.F. Gauthier, and J.P. Laforest. 2006. Hormones in bovine milk and milk products: A survey. Review. International Dairy Journal. Pages 1408-1414
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