Hormones in Milk

Red and White Holstein

By Allen Young, Extension Dairy Specialist & Associate Professor Utah State University 

Hormones and their relationship to food are a hot topic, but… What are they? Are they in my food naturally? Are they added to foods? What impact do they have on the body? To answer these questions and understand the impact of hormones, we need to learn a little about them.


The study of hormones is called endocrinology, a term taken from the classical definition of hormones, which states that they are messenger compounds secreted by ductless glands in the body (endocrine glands) that cause an effect on another organ, tissue or cell. In order to be biologically active and do their job properly, each specific hormone needs a very specialized protein located on the organ, tissue, or cell where they have an effect. These are called receptors and their job is to bind the hormone and start/cause their unique effect.  Think of it as a ball in a mitt.  As individual entities, the two have little effect, but, in baseball, a pop-fly that is caught results in an “out” and a potential cascade of effects. An example of this in action is the hormone insulin. Floating around in the blood stream, insulin is inert but once it binds to an insulin receptor on cells, the compound is able to pull sugar molecules from the bloodstream into the cells. When working properly, this process keeps our blood sugar from getting too high. Extreme problems with this particular hormone/receptor mechanism can be described as diabetes.

Types of Hormones:

Hormones can be categorized into two broad classifications: steroids and protein hormones (amino acids).  Examples of steroid hormones are estrogen, progesterone and testosterone.  Examples of protein hormones include growth hormone, insulin, or prolactin.  The human body produces over 50 hormones and could not function without them.

In addition to the hormones your body makes, there are other sources of hormones. Animals and plants produce hormones naturally, so we eat hormones in our food all the time, but the amounts we take in are low compared to what our bodies produce naturally.  Let’s use estrogen as an example.

Screen Shot 2014-11-10 at 9.09.21 PMHormones in Milk – rBST:

What happens when you give synthetic hormones to animals and then eat the meat or milk?  Basically the story is the same as above.  Any hormone you eat will be totally or partially degraded in the stomach (protein hormones) or the liver (steroids).  In the case of bovine somatotrophin (bovine growth hormone often abbreviated as rbST), not only is it degraded in the stomach, but the structure and receptors in humans won’t work with the bovine (cow) version of the hormone.  This hormone is species specific and inert in humans.What effect does ingesting these hormones have on our body?  The short answer is that only about 2-5% of the hormones we eat actually make it into our body because of inactivation during digestion. Of the protein hormones that we eat, essentially all of the hormone is broken down in the stomach and has no effect.  Steroids get inactivated as they pass through the liver.  When eaten in normal, moderate amounts, dietary hormones have essentially no effect on our body and its ability to do its job.

The Take-Home:

So, should you be concerned?  Probably not.  Our bodies produce the same hormones that we routinely ingest in food but in amounts that tend to dwarf the amounts we eat.  Normal intake of these foods should not have any effect on the body since the stomach and liver inactivate hormones through natural digestion. As in all dietary practices, moderation is key since excessive consumption of any one food can throw the body out of balance.

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    Good hormones

    February 25, 2015 at 4:23 pm
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    Wowl very interesting! Now explain me why is doctors concerned about it? I have had at least 3 friends that different doctors has taking their girsl off milk due to the hormones and their were told to continue to eat meat but try to either not consume too much or choose meat from no added hormones. I heard that so many time from different people that I asked those friends if they felt it was better or did the problem with their girls improved and the answer was yes! Now Im very confused with this post? Could this low amount be enough to cause problems?

    February 25, 2015 at 8:42 pm
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    I too am curious as to why Dr. Are telling parents that their daughters need to avoid or cut down on milk and meats as this foods have the least amount of hormones. Is it all coming down to the amounts in excess that people are eating that is affecting them or maybe it is they are eating more vegetables? Please help explain this…

    February 26, 2015 at 6:24 am

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