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Cows and Hormones

Are artificial growth hormones to increase cows' milk production allowed in Canada? No. Growth hormones, such as recombinant bovine somatotropin (rbST), have not been approved for sale in Canada.

Bovine somatotropin (bST) is a hormone that occurs naturally in bovines; it regulates growth and lactation. BST has no effect on humans.1 Recombinant bST (rbST) is a commercially produced version of the natural hormone and it can increase milk production by 10% to 15%.2 But it may also increase the risk of mastitis and infertility and cause lameness in cows,3 which is why Health Canada has not approved it.It is important to note that rbST has not been shown to have a negative effect on human health4 and its use is permitted in other countries (such as the United States), where it is considered safe.

Estrogen in Milk
As per all animal products, estrogen is naturally found in cow’s milk and dairy products. Some plant-based products such as soy also contain estrogen.

A 2012 study was performed in order to quantify and compare the amount of estrogen, Estrone E1 and Estrone sulfate E1S (inactive endogenous steroid) concentrations in whole milk and its skim and fat fractions. Here are the major findings of this study5:

  • Approximately 90% of ingested hormones (including estrogens) are inactivated by the gastrointestinal and hepatic system immediately upon absorption5
  • Quantity of E1 and E1S in 3 glasses of milk (237 mL): 68 ng/day
  • Endogenous production of total Estrone E1 (E1 + E1S) and E2
    • 54,000 ng/day: Prepubertal girls
    • 100,000 ng/day: Prepubertal boys
    • 140,000 ng/day: Men
    • 630,000 ng/day: Women

In terms of the consumption of milk products, 3 glasses of milk represents only 0.001% to 0.1% of individuals’ endogenous estrogen production rates.5

Milk Consumption and Cancer
According to the World Cancer Research Fund, the authority on the role of diet and cancer, there is no strong evidence that milk or milk-products increase the risk of any cancers including hormone sensitive cancers such as breast, ovarian and prostate.6 Additional information concerning milk products and cancer may be consulted at:

Growth hormones are not allowed in Canada. Additionally, the amount of naturally occurring hormones in dairy products is insignificant compared to endogenous production. These negligible effects should rule out concerns regarding reproductive disorders or hormone imbalances based on the consumption dairy products.


1. Report of the Canadian Veterinary Medical Association Expert Panel on rBST. Executive Summary. Can Vet J 1999; 40:160-2.

2. Dohoo IR et al. A meta-analysis review of the effects of recombinant bovine somatotropin. Part 1. Methodology and effects on production. Can J Vet Res 2003. 67:241-51.

3. Dohoo IR et al. A meta-analysis review of the effects of recombinant bovine somatotropin. Part 2. Effects on animal health, reproductive performance, and culling. Can J Vet Res 2003. 67:252-64.

4. Report of the Royal College of Physicians and Surgeons of Canada Expert Panel on Human safety of rbST, 1999. Health Canada.

5. Macrina A et al. Estrone and Estrone Sulfate Concentrations in Milk and Milk Fractions. J Acad Nutr Diet. 2012. 112:1088-93

6. World Cancer Research Fund / American Institute for Cancer Research. Continuous Update Project Report. Colorectal Cancer 2017 Report. Food, nutrition, physical activity, and colorectal cancer. 2017.

Keywords: bovine growth hormone

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