Hormones: What’s In Your Milk?

By Alvaro Garcia

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

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*
 

*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.