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Bovine growth hormone in milk - what are the risks? - Nutrition Myths
Is milk from cows fed with growth hormones bad for you?


  • There is insufficient evidence to conclude that milk from cows injected with recombinant bovine growth hormone (rBGH) is safe for long term consumption.
  • Many countries consider the use of these hormones unsafe for cattle. They have, therefore,  made them illegal for human consumption.
  • The use of rBGH was not approved by the European Union countries, Canada, Australia, New Zealand and Japan.
  • Drinking milk from the rBGH treated cows over a long period of time, may have potentially harmful consequences, especially the increased risk of breast, colorectal and prostate cancers and health consequences related to the development of antibiotic resistant bacteria.
  • The safest approach is to choose milk from cows that have not been treated with rBGH, preferably organic.


Bovine growth hormone in milk – what are the risks?

Milk is known for its many health benefits, but also for its health risks such as milk protein allergy, lactose intolerance and bovine growth hormones. 

The application of bovine growth hormones to increase the production of cow’s milk is a controversial subject.

Most of the health concerns related to the use of hormones in cows comes from injecting them with the hormone rBGH, also called recombinant bovine somatotropin (rBST).

Although this bovine growth hormone has been proven not to be active in humans, since it appears not to directly present any health problems, there are two indirect potential health effects associated with the presence of this hormone in milk:

  1. Injecting cows with rBGH increases the amount of a protein hormone called IGF-1 in milk.

    A higher level of IGF-1 in blood is associated with prostate, breast and colorectal cancers in humans.

    Does drinking milk with an increased IGF-1 content cause an increase of IGF-1 in human blood and if so, does it increase the risk of developing cancer?

  2. Injecting cows with rBGH causes mastitis in cows (udder infection).

    As a result, two things happen: pus from the infected udders gets passed to the milk and the infected cows are given more antibiotics than the rBGH-free ones.

    Obviously having milk with cow’s pus is not desirable, but does the process of adding these extra antibiotics create more antibiotic-resistant bacteria, posing health risks for humans?

These two pertinent question are still to be answered, either by the companies producing the bovine growth hormones, governments or by large, complete and independent scientific studies.

Please note that regardless the results of the studies on the health effects on humans, injecting cows with rBGH causes mastitis, foot problems, and adverse reactions to the site of injection in cows, and, therefore, is considered unethical by many people.

As a result, on these grounds, its use was banned in the EU, Canada, Australia, New Zealand and Japan. (1)

Note: non-rBGH milk consumption is generally considered safe. A meta-analysis found some evidence of the connection between milk consumption and the risk of developing breast cancer. However, another meta study (2) found no association (3).

The use of growth hormone in cows

A naturally occurring hormone in cows called bovine growth hormone (BGH) or bovine somatotropin, is produced by the pituitary glands of cattle and is present in cow’s milk.

This is one of the reasons why messages such as “hormone-free milk” on the labels are not allowed.

The recombinant bovine growth hormone (rBST) is a synthetic hormone, similar to BGH, and was designed to increase milk production by up to 20% when injected into a cow.

It was approved in the United States in 1993 and first used by a company called Monsanto.

The controversy and uncertainty of the health risks decreased the demand for rBGH milk and currently less than 20% of cows are injected with this hormone.

Many milk manufacturers advertise bovine growth hormone free milk. (4)

There are claims that the scientific studies that endorse the hormones’ safety are either performed by Monsanto, are insufficient or not all of the details (raw data of the studies) are published since it may harm the companies’ interests. (5, 6)

Some countries found that there was limited evidence on the safety for humans and they had concerns about animal health. Therefore, the use of rBST is illegal in the European Union countries, Canada, Australia, New Zealand and Japan. (1)

Is there a health risk from excess of IGF-1 in cow’s milk?

In summary, the original studies approved by FDA do not prove that the excess of IGF-1 in milk as a result of rBST is free of risk, and the available independent studies indicate that the association with an increased health risk exists and may be linked to various cancers.

Although biologically inactive in humans, rBGH increases the bioactive insulin-like growth factor-1 (IGF-1) in cow’s milk. The increase varies from small to significant depending on the study.

According to a European Commission’s report, the concentration of IGF-1 in milk from the cows treated with rBST is 2 to 5 times higher than in non-treated cows.

Other studies have shown that these amounts were not as high but still significant. The difference between these results could be due to the influence of lactation stage, nutritional status and the age of the animals tested.

Toxicity studies on the effects on humans of the IGF-1 from milk consumption have not been done yet. The only studies performed were a few weeks’ studies on rats injected with IGF-1.

The results were inconclusive whether a long-term consumption of milk with higher levels of IGF-1 has an impact on cancer risk or other health issues.  (7)

What is known is that the IGF-1 in humans and cows is identical and that the pasteurization process of the milk doesn’t make IGF-1 inactive.

It is also proven that an increased level of IGF-1 in  human blood is related to a higher risk of developing breast, colorectal and prostate cancers.

Does milk from antibiotic injected cows to treat mastitis pose a health risk for us?

In summary, the evidence is insufficient and, therefore, rBGH use in cows should never been approved.

Cows are normally injected with antibiotics to prevent diseases caused by bacteria, as a preventive measure (to prevent pneumonia in calves), to help cattle grow faster or to improve feeding efficiency (usually smaller amounts in this case).

The decision of how much antibiotics are given to cattle is up to the keepers.

In order to reduce, within safe limits, the concentration of antibiotics in the cattle’s body, it is crucial to guarantee a withdrawal period. Each antibiotic has a different withdrawal time.

In general, the amount of antibiotics in the meat and milk products available for human consumption are within safe limits.

Heavy fines are applied for not complying with the safe standards and there have been extremely few violations registered.

The use of rBGH is associated with an increased incidence of mastitis and other health complications in cows. These cows, therefore, receive extra amounts antibiotics to fight the health problems.

The additional antibiotics have been shown to cause the development of antibiotic-resistant bacteria. Unfortunately, it is unclear, from the available studies, to what extent it affects human health.

Controversy of Monsanto ethics

There is a controversy surrounding Monsanto’s tactics.

Claims such as offering bribes, manipulation of movement of staff between Monsanto, the U.S. government and the FDA (revolving door), misrepresentations about their findings and the safety of their products, suing farmers,  manipulating the scientific data to gain product approval and influencing changes to regulatory processes, are  some examples.

I strongly encourage you to view in full these two documentaries and make your own conclusions on this matter.



In the light of the above, the studies conducted on the effects of rBGH on health are insufficient for the product to be considered as safe for human consumption.

These are just a few reasons why these studies are limited: (7):

  1. Early studies on the hormone effects on the human health were performed by the very companies seeking its approval (e.g. Monsanto) and, therefore, can be biased.
  2. Based on these studies, the latest approval of rBGH was in 1993 by the FDA. Since FDA doesn’t routinely review their decisions, the original approval still stands, even though recent studies question the conclusions of the initial studies and the resulting approval.
  3. The studies performed by Monsanto and held in the hands of FDA are not fully disclosed to non-FDA scientists, but only published as summaries. This makes it impossible for an independent scientist to verify the validity of the conclusions.
  4. The usual approval process by FDA has been modified to allow Monsanto to skip the usual product safety tests, enabling the untested, potentially dangerous product on the market.
  5. To complicate things even further, it may take several years from the time of the request submission of the referred studies to Freedom of Information Act. It is difficult, therefore, to determine what the original studies actually prove or didn’t prove.
  6. There is controversy surrounding Monsanto’s honesty and the questionable arrangement with FDA.

The American Cancer Society doesn’t have an official position,  due to lack of evidence. (8, 9)


You will find a summary of the most common nutrition myths and evidence-based nutrition facts here.


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