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Are there steroid hormones in protein supplements? Thousands of people consume protein supplements every day. Most of these supplements contain proteins extracted from cow’s (bovine) milk, namely whey and casein. Cows secrete various steroid hormones into their milk. So is it possible that consumers are unknowingly ingesting steroid hormones when they drink a protein shake?

I posed the above question to Dr. Ernst Rattenberger at Tiergesundheitsdienst (Animal Health Services) Bayern e.V. in Germany. Below is our discussion. If, after reading it, you’re left scratching your head, you’re not alone. Based on Rattenberger’s answers, it seems likely that you will be ingesting some steroids when you drink a protein shake. Will you ingest enough to promote cancer or cause some other undesirable effect? I don’t think we can answer that question definitively one way or another.


“Dear Dr Rattenberger:  As you may know, protein supplements are widely consumed here in the United States. Typically these products contain whey protein isolate and/or whey protein concentrate. Also included may be casein, caseinates and/or milk protein isolate.

Are you aware of any evidence to suggest that these protein supplements may contain steroid hormones, being that they are derived from bovine milk?

Thank you very much for any insights you can provide.

Dr. Rattenberger:

“Mr. Thoburn. Concerning your question about the occurrence of steroids in milk derived products, I like to give you some information about the physiological background. Steroids in milk are reflecting the different stages of  cyclicity and pregnancy. Progesterone is present during pregnancy and responsible for the maintenance of a gestation. Depending on the fat content of a milk powder its concentration is in the ppb [parts per billion] range Estrogen concentrations (estrone, estradiol-17ß and estradiol-17α) increase with the duration of pregnancy from second to third trimester.

Now, milk in our regions represents an average of the different pregnancy states, because there is nearly no seasonality in calving in comparison to situations like in New Zealand (seasonal calving). Sixty to 70% of the milk in our regions is obtained from pregnant cows and only 10% from cows in the third trimester. This means that the concentrations of estrogens in milk powder or whey milk powder show minor deviations. Below are some examples of the estrogen contents of milk protein concentrate (µg/kg):

Estradiol-17ß:             0.13

Estrone:                      2.6

Estradiol-17α:             0.61

In comparison to estradiol-17ß,  the oral activity of estrone will be 0.5 and 0.1 for Estradiol-17α (Herr et al. 1970). Concentrations of androstendione [a precursor to testosterone and estrogen] are in the ppb range and may sometimes exceed 10µg/kg. I hope my answers were satisfying. Please do not hesitate for further questions.

Dr.Ernst Rattenberger
Tiergesundheitsdienst Bayern e.V.
Bereich Lebensmittelhygiene
Senator-Gerauerstr. 23
85586 Poing


“Thank you for answering my question, Dr. Rattenberger. It was generous of you to do so.

Is it conceivable that estrogens or androgens, at the concentrations present in commercially available milk protein powders (e.g. whey) might have physiological effects in humans? Or are the concentrations too low? For instance, if a man or woman were to consume 50-100 g of whey protein every day, could they ingest enough androgens and/or estrogens to have physiological effects?

Thanks again for your time. I appreciate it greatly.”

Dr. Rattenberger:

“Dear Mr. Thoburn: Based on a No Effect Level (NOEL), risk assessment of the JECFA (Joint FAO/WHO Expert Committee on Food Additives) from February 1999 at  the 52nd meeting, established an “acceptable daily intake (ADI)” of 50 ng Estradiol-17ß / kg body weight.

The calculated estrogen content of 100g of  milk protein concentrate for a person with 60kg [132 lb] body weight is far below this limit. (Similar for androstendione.) One of the concerns about exposure to estrogens is their carcinogenicity (see introduction to our paper [1]). It is not possible for me to comment on this, nor to give any limits [to safe levels of protein supplement consumption.]”


1. http://www.ncbi.nlm.nih.gov/pubmed/21268636 NOTE: I was referred to Dr. Rattenberger after contacting one of the authors of this paper. He is also an author of it.