Cow milk naturally contains several hormones that are produced by the cow’s endocrine system. In addition, some farmers may also inject cows with artificial growth hormones to increase their milk production. The latter hormones are not found naturally in cow’s milk and some believe they can be harmful when consumed.

Natural hormones in cow milk include:

  1. Insulin-like growth factor 1 (IGF-1): This hormone plays a role in the growth and development of cows. It is also present in human milk and has been linked to cancer. However, studies have not consistently found evidence that consuming cow milk containing IGF-1 is harmful to human health.
  2. Prolactin: This hormone stimulates the production of milk in lactating cows. It is also present in human milk and plays a role in the development of the breast tissue.
  3. Estrogen and progesterone: These steroid hormones are produced by the ovaries and play a role in the cow’s reproductive system. They are also present in cow milk in small amounts.
  4. Prostaglandins: These hormone-like compounds are produced by the cow’s body and play a role in the regulation of inflammation and blood flow.
  5. Other hormones: There are other hormones present in cow milk such as melatonin, oxytocin, and thyroid hormones.

It is important to note that the levels of these hormones in cow milk vary depending on the stage of lactation, the cow’s diet, and other factors. In general, the levels of hormones in cow milk are very low and are considered safe to consume. The Food and Drug Administration (FDA) and other regulatory agencies consider cow milk to be a safe and nutritious food.

Artificial hormones

The two main hormones that are used in this way are recombinant bovine somatotropin (rBST) and recombinant bovine growth hormone (rBGH). These hormones are genetically engineered versions of hormones that cows naturally produce and are administered to the cows via injections.

The use of artificial hormones in cow milk has been a controversial topic, with some studies suggesting that milk from cows treated with rBST may contain higher levels of a growth hormone called insulin-like growth factor 1 (IGF-1), which has been linked to an increased risk of certain cancers. However, other studies have not found any significant difference in the levels of IGF-1 in milk from treated cows compared to untreated cows.

The use of rBST is prohibited in the European Union and Canada, and many US dairies have chosen not to use it because of consumer concerns. In the US, milk from cows treated with rBST must be labeled as such, but milk from untreated cows is not required to be labeled.