by Heather A. Goesch, MPH, RDN, LDN
June is Dairy Month. All cow’s milk, like human milk, inherently contains growth hormones. Among the most publicized is bovine growth hormone (BGH), or bovine somatotropin (BST) – a hormone that cows naturally produce. The synthetic form, rBGH or rBST, is given to cows to extend the lactation period by increasing levels of another hormone, insulin-like growth factor (IGF-1), ultimately increasing milk production with less feed, less animal waste and less methane production.
Unfortunately, there is a great deal of confusion about these hormones, as well as the use of antibiotics. While more research is warranted, here’s where we are thus far regarding some of the more common concerns:
- Does drinking milk that contains these hormones increase a person’s individual level of hormones? Testing has found no significant difference between the levels of growth hormone between milk of rBGH-treated cows and non-rBGH-treated cows. Additionally, the human stomach naturally breaks down protein hormones, rendering them inactive. Furthermore, bovine growth hormones are just that – bovine, meaning they are not recognized by human protein receptors.
- Can consumption of milk from rBGH-treated cows that may have increased levels of IGF-1 increase risk of certain cancers in humans, particularly prostate and breast? While early studies suggested such, the most recent research does not confirm these initial associations, or demonstrates much weaker associations. What we know now seems to suggest that there is no cause and effect chain linking these two hormones to increased risk of cancer or other disease in drinking milk with rBGH. The exact relationship requires further study.
Still, milk from rBGH-treated cows was found to have slightly higher IGF-1 concentrations than untreated milk. Though the human digestive system would likely break down and deactivate any IGF-1 in our milk, it is yet unclear as to whether or not, and if yes, to what extent, the hormone may be absorbed. Researchers compared blood draws of adults who drank milk (3 glasses/day) vs. those who drink little to no milk, finding that the former had about 10% higher levels of IGF-1. However, this exact same finding was also reported in adults who drank only soy milk (no cow’s milk), suggesting the IGF-1 increase may actually be the result of a different nutrient or entirely other factor unrelated to rBGH.
- Treating cows with rBGH can result in mastitis, which can lead to antibiotic use that promotes the development of antibiotic-resistant bacteria. While antibiotics are used to treat mastitis and other infections in cows, the farmers have a financial incentive to avoid antibiotic use unless absolutely necessary. Among other reasons, sick cows are generally separated from the herd for special care, increasing labor- and housing-related cost burdens. An even greater deterrent is the FDA requirement that during and for 96 hours following antibiotic treatment, a treated cow’s milk must be discarded, i.e., wasted without profit. Furthermore, incoming milk tanker trucks are mandatorily tested at dairy processing plants upon arrival. If a tanker’s load – often comprised of milk from more than one farm – is found to contain any level of antibiotics, the offending milk can be traced back to the specific farm. That farm is then on the hook for the disposal and shipping costs of both its own wasted milk plus that from any other farms, and repeat violations jeopardize their ability to sell milk at all. Thus, treatment without antibiotics is highly preferred.
Despite best efforts, it is possible that milk containing antibiotics can make it into our refrigerators, but as yet the extent to which these are, or are not, transmitted to humans is unclear. In terms of cancer and other diseases, evidence thus far suggests that there is no increased risk associated with drinking pasteurized milk from cows treated with antibiotics.
Stay tuned. More research is warranted, and underway. As of this time the American Cancer Society has “no formal position regarding rBGH,” and goes on to state that “it is not clear that drinking milk, produced with or without rBGH treatment, increases blood IGF-1 levels into a range that might be of concern regarding cancer risk or other health effects.”
For those who are truly concerned, there is also no significant human health risk in drinking milk without hormones or antibiotics. The only downfalls are higher price, and the possibility of purchasing milk that has become tainted (taste sour or spoiled) as the result of untreated infection.
Routinely used antibiotics for cows are ampicillin and erythromycin. And for anyone who is extremely sensitive or allergic to ampicillin, erythromycin, or similar antibiotics, avoidance of treated milk is likely wise to avoid any potential problems.
What are your thoughts on dairy milk hormones and antibiotics?
- American Cancer Society, Recombinant Bovine Growth Hormone
- Today’s Dietitian, Organic Milk and Meat—Are They Healthier than Their Conventional Counterparts?
- US Food and Drug Administration, Report on the Food and Drug Administration’s review of thesafety of recombinant bovine somatotropin