Are you interested in the specific hormone marketed by Monsanto as Posilac in the US (bovine growth hormone: rBGH/BST)?
To answer your question of "where?" in brief: an excellent place to start is at the U.S. Government's site PubMed at www.pubmed.gov PubMed provides abstracts of the bulk of journal articles published in the medical field. The research can be quite up-to-date, as you will see below-- I cite 2 articles that have yet to be published!
Search terms such as rBGH or BST (as well as IGF-1) will yield results there. Terms I used in my search engines included those, as well as "Bovine Growth Hormone." Medical searching can become quite specialized. I am not a medical librarian, so cannot guarantee that I have turned every stone. If you need guarantees, please let me know and I will ask for help from a specialist (or you can ask a local medical librarian in your town!). Additionally, once this response is finalized it will be posted to the website, where it will be available for viewing and additional comments as well.
In the course of this response I use the terms rBGH, BST and rBST interchangeably.
As far as I can tell, there have been no controlled human studies aimed at determining the human health impact of milk produced in an rBGH laden cow. An opponent of the hormone, however, stated in 1994: "FDA says this possibility is "insignificant" and has refused to conduct human tests. [2] Whether people exhibit immune responses or allergic reactions to rBGH will now be discovered by exposing the general public to this drug. In essence, FDA has given rBGH producers permission to conduct a large-scale experiment on the public, without a control population." ( http://www.rachel.org/bulletin/index.cfm?issue_ID=744 )
There is emerging information that may support the need for such a human study.
Monsantos' site: http://www.monsantodairy.com/
This page lists the countries that have approved rBST for either animal or human consumption: http://www.monsantodairy.com/faqs/countries-rbst.html
A side issue is that many countries that have accepted its safety for humans do not find it to be safe for cows...
Monsanto also offers a links page to sites that support the safety of rBST: http://www.monsantodairy.com/links/index.html
The hormone has been approved for use in the USA, thus has undergone a study by the FDA. The FDA did not require human trials. An abstract of the original approval can be found at: www.fda.gov/cvm/FOI/140-872FONSI.pdf
In 2005, they reviewed the approval. This is a link to their defense of the continued use of Posilac in the U.S.: http://www.fda.gov/cvm/RBRPTFNL.htm
The United Nations also approved BST. A press release can be found at: http://www.fao.org/NEWS/1998/980301-e.htm
Unfortunately the link to the original report is dead- please let me know if you would like me to track it down.
On the flip side, the Organic Consumer's Association follows the latest studies. For example, they cite the May 22, 2006 issue of Scientific American which features a study on a rise in twin births that theorizes that the difference between the number of twin births in the US and UK might be attributable to rBGH.
The Organic Consumer's page is here: http://www.organicconsumers.org/2006/article_512.cfm (this is lifted, word-for-word, from Scientific American's page at: http://www.sciam.com/article.cfm?chanID=sa011&articleID=00094DF5-2CC5-1471-ACC583414B7F0000 ).
Steinman's study in the Lancet:
Can the chance of having twins be modified by diet?
Steinman G
The Lancet - Vol. 367, Issue 9521, 06 May 2006, Pages 1461-1462
Steinman's study in May's issue of the Journal of Reproductive Medicine: http://www.reproductivemedicine.com/TOC/Toc.htm
The current issue that is gaining the most attention regards a potential relationship between the increased levels of IGF-1 found in rBGH milk and cancer.
In 2002, the Organic Consumer's Association posted this article on the potential relationship between IGF-1 (a component of cow's milk that could be increased by rBGH ) http://www.organicconsumers.org/rbgh/cancer091302.cfm
At the time, the researchers cautioned that "more research is needed." http://www.organicconsumers.org/rbgh/cancer091302.cfm
Fox news terminated two reporters who attempted to report on the possible link between IGH-1 and cancer. A website about the resulting lawsuit can be found here: http://www.foxbghsuit.com/
Two articles on the effects of IGF-1 and its relation to human nutrition have just been published in this month's issue of the journal "Endocrine-Related Cancer:"
ARTICLE 1:
Rinaldi S, Peeters PH, Berrino F, Dossus L, Biessy C, Olsen A, Tjonneland A, Overvad K, Clavel-Chapelon F, Boutron-Ruault MC, Tehard B, Nagel G, Linseisen J, Boeing H, Lahmann PH, Trichopoulou A, Trichopoulos D, Koliva M, Palli D, Panico S, Tumino R, Sacerdote C, van Gils CH, van Noord P, Grobbee DE, Bueno-de-Mesquita HB, Gonzalez CA, Agudo A, Chirlaque MD, Barricarte A, Larranaga N, Quiros JR, Bingham S, Khaw KT, Key T, Allen NE, Lukanova A, Slimani N, Saracci R, Riboli E, Kaaks R. Related Articles, Links
IGF-I, IGFBP-3 and breast cancer risk in women: The European Prospective Investigation into Cancer and Nutrition (EPIC).
Endocr Relat Cancer. 2006 Jun;13(2):593-605.
Abstract:
"Blood concentrations of insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-3 (IGFBP-3) have recently been associated with breast cancer risk, notably in women who developed breast cancer at a young age. Prospective studies published so far, however, were relatively small and odds ratio (OR) estimates imprecise. We present the results of a large prospective case-control study nested within the European Prospective Investigation into Cancer and Nutrition on total IGF-I, IGFBP-3 and breast cancer risk including 1081 incident cases of invasive breast cancer and 2098 matched control subjects. Increasing IGF-I and IGFBP-3 concentrations were associated with a significant increase in breast cancer risk in women who developed breast cancer after 50 years of age (highest vs lowest quintile OR 1.38 (95% confidence interval (CI) 1.02-1.86), P = 0.01, and 1.44 (95% CI 1.04-1.98), P = 0.01, respectively), but no relationship was observed in younger women (OR = 1.03 (95% CI 0.60-1.77), P = 0.81 for IGF-I, and OR = 0.92 (95% CI 0.50-1.70), P = 0.69 for IGFBP-3). There was, however, significant heterogeneity in the relationship of breast cancer with serum IGF-I and IGFBP-3 levels depending on the time interval between blood donation and tumor diagnosis. A reduction in breast cancer risk with increasing IGF-I concentrations was observed in cases with a diagnosis of cancer less than 2 years after blood donation, (OR = 0.76 (95% CI 0.57-1.03)), while an increase in risk was observed for women with a later diagnosis (above or equal to two years after blood collection, OR = 1.51 (95% CI 1.19-1.91)). A similar pattern was observed for IGFBP-3. This study confirms previous findings for an association of serum IGF-I and IGFBP-3 concentrations with breast cancer risk, particularly for women with a later diagnosis of cancer, but it does not support the hypothesis of an involvement of IGF-I in younger women."
ARTICLE 2:
Endocr Relat Cancer. 2006 Jun;13(2):583-592. Related Articles, Links
Insulin-like growth factor-I, its binding proteins (IGFBP-1 and IGFBP-3), and growth hormone and breast cancer risk in The Nurses Health Study II.
Schernhammer ES, Holly JM, Hunter DJ, Pollak MN, Hankinson SE.
Channing Laboratory, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, 181 Longwood Avenue, Boston, Massachusetts 02115, USA.
Abstract:
Earlier data suggest that the relationship between circulating insulin-like growth factor I (IGF-I) levels and breast cancer risk differs according to menopausal status. We evaluated the association between IGF levels as well as the primary regulator of IGF-I production, growth hormone (GH), and breast cancer risk in the Nurses' Health Study II (NHS II) cohort, a large cohort of primarily premenopausal women. We conducted a case-control study nested within the prospective NHS II cohort. Plasma concentrations of IGF-I, IGF binding protein (IGFBP)-3, IGFBP-1, and GH were measured in blood samples collected between 1996 and 1999. Totally 317 women were identified who had a diagnosis of invasive or in situ breast cancer between the date of blood collection and June 1 2003; 75% of these women were premenopausal at blood collection. To each of the 317 women, two controls were age-matched for a total of 634 controls. We used conditional logistic regression models to estimate the relative risk of breast cancer. Overall, plasma IGF-I, IGFBP-1, IGFBP-3, and GH levels were not associated with breast cancer risk (relative risks, top vs bottom quartile; IGF-I, 0.98, 95% confidence interval (CI), 0.69-1.39; IGFBP-1, 0.95, 95% CI, 0.63-1.41; IGFBP-3, 1.10, 95% CI, 0.78-1.54; GH, 1.09, 95% CI, 0.82-1.46). These risks were similar for premenopausal women of age 45 years or less. Further adjustment for additional breast cancer risk factors did not change these estimates. In conclusion, circulating IGF-I, IGFBP-1, IGFBP-3, and GH levels appear to have no important association with breast cancer risk in a large cohort of premenopausal women.
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Monsanto itself found that use of rBGH increased the levels of IGF-1 in milk ( http://www.monsantodairy.com/about/human_safety/index.html )
The original study is:
Collier RJ, Miller MA, Hildebrandt JR, Torkelson AR, White TC, Madsen KS, Vicini JL, Eppard PJ, Lange GM: Factors affecting insulin-like growth factor-1. Concentration in bovine milk. J Dairy Sci 1991;74:2905.
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This is the abstract & citation for the study that showed that casein (found in milk) increased the digestive absorption of IGF-1 in rats:
Br J Nutr. 1990 May;63(3):521-34.
Effect of dietary proteins on the plasma immunoreactive insulin-like growth factor-1/somatomedin C concentration in the rat.
Takahashi S, Kajikawa M, Umezawa T, Takahashi S, Kato H, Miura Y, Nam TJ, Noguchi T, Naito H.
Department of Agricultural Chemistry, Faculty of Agriculture, University of Tokyo, Japan.
Abstract:
Plasma immunoreactive insulin-like growth factor-1/somatomedin C (IR-IGF-1) was determined in rats fed for 1 week on a protein-free diet, or diets containing gluten, gluten supplemented with lysine and threonine, maize-gluten meal (with arginine), maize-gluten meal (with arginine) supplemented with tryptophan and lysine, or casein. IR-IGF-1 concentration was higher in the arterial plasma of rats fed on a diet containing casein at 120 g/kg diet (4-8 U/ml) than in rats fed on a protein-free or a low-casein (50 g/kg diet) diet (1.5-2 U/ml). The plasma of rats fed on gluten or maize-gluten meal as the protein source showed intermediate values. However, giving a diet containing an amino acid mixture as recommended by the National Research Council (1978) but deprived of lysine or tryptophan did not affect significantly the plasma IR-IGF-1 concentration. Total IGF-1 concentration (which was measured immunologically after extraction of the plasma with acid-ethanol) was also lower in the rats fed on the protein-free diet than in those fed on the casein (120 g/kg diet) diet. The ratio IR-IGF-1:total IGF-1 was higher in the rats fed on the casein diet (120 g casein/kg diet) than in those fed on the protein-free diet. The results suggest an important influence of IR-IGF-1 or IR-IGF-1:total IGF-1 ratio on protein anabolism and nutrition. IR-IGF-1 and total IGF-1 were found in the fractions of molecular weights 40 kDa and 150 kDa after gel filtration of rat plasma. A larger amount of IGF-1 was recovered in the fraction of 150 kDa in the rats fed on the casein diet. 125I-IGF-1 added to the plasma of rats fed on the protein-free diet was found mainly in the fraction of 40 kDa after gel-filtration. On the other hand, 125I-IGF-1 added to the plasma of rats fed on the gluten or casein diets was mainly recovered in the free IGF-1 fraction. The results suggest that IGF-binding protein(s) of molecular weight about 40 kDa was not saturated with IGF-1 in the rats fed on the protein-free diet. The results indicate the important role of IGF-1 and its binding proteins in the regulation of protein metabolism in rats.
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There is a huge amount of information available on this hotly debated issue. I limited my citations to the articles I found to be most frequently cited. Additional articles may be found in the bibliographies for these papers/web pages. Please let me know if this answer meets your needs, or if there is anything else you require so I can move this post through the process to finalizaton.
