HORMONES
Milk naturally contains very small amounts of hormones, like all foods do. This is because hormones are simply proteins that carry chemical signals in the body of an organism, whether it is celery or salmon. However, the body breaks these naturally produced hormones found in food down during digestion, meaning they instantly become inactive.
Although there is no such thing as ‘hormone-free’, you can opt to buy milk produced by cows that have not been given extra bovine growth hormone, which will be indicated on the product label.
Recombinant bovine somatotropin (rBST), sometimes called recombinant bovine growth hormone (rBGH), is a synthetic version of the naturally occurring protein that helps cows produce milk. It is species specific and therefore works only in cows.
All animals, including humans, produce growth hormones naturally in the pituitary gland. This protein is necessary for normal growth and development. Some farmers choose to use a supplemental bovine growth hormone to help cows produce more milk. The United States Food and Drug Administration (FDA) has confirmed that milk from cows given bovine growth hormone is safe for consumption.
Hormones and growth factors are produced naturally by a cow during milk production (also see previous answer). These quickly break down during digestion. Insulin-like growth factor 1 (IGF-1) is a peptide hormone that is produced by the liver – an organ that is part of the digestive system – in response to the pituitary gland’s secretion of growth hormone. However, the concentration of IGF-1 in cow’s milk is much lower than the concentration of IGF-1 in the digestive fluids in the gastrointestinal tract, and is simply too low to have any effect on human health when we drink milk.