Some studies on milk

[vindiesel]

Is milk (dairy) good for us?

Hormones and Milk

Cow’s milk naturally contains a number of protein (peptide) and steroid hormones in very low concentrations 1-5. Among the protein hormones present in milk are prolactin (in an amount of about 50 micrograms (µg)/liter of cow’s milk) and gonadotropin-release hormone (present at about 1-5 µg/liter)1. Steroid hormones which are present in very low quantities in cow’s milk include the glucocorticoids, cortisol and corticosterone (0.2-0.6 µg/liter), and the ovarian hormones-progesterone (10-30 µg/liter), estrone (30 µg/liter), and estradiol (175 µg/liter)1.

The concentration of hormones in cow’s milk is very minimal relative to the level of normal human hormone production and, as such, is of little physiological significance. For example, an 8-ounce serving of milk contains about 29 nanograms (ng) (a nanogram is a billionth of a gram) of the hormone estrogen 5. The average nonpregnant adult female, by contrast, produces 480,000 ng estrogen/day 5. Intake of two servings of milk/day, therefore, provides a negligible amount of about 0.012% of the quantity of estrogen normally produced by a nonpregnant female.

The U.S. Food and Drug Administration (FDA) has approved a number of natural and synthetic hormones (e.g., estradiol, progesterone) to promote growth and feed efficiency in dairy cattle 6, 7. Scientists at both the World Health Organization (WHO) and the FDA have concluded that livestock hormones approved to-date pose no threat to human health when used in recommended doses and in compliance with recommended animal treatment practices 6.

The FDA has approved use of bovine somatotropin (BST) for use in lactating cows to increase milk production by up to 20% and to improve milk production efficiency 8. Somatotropin is a naturally occurring protein hormone that regulates growth and lactation and is produced by the pituitary gland in both man and animals 9-14. As a result of new technologies (i.e., genetic engineering), bovine somatotropin now can be synthesized by scientists, making it widely available 9-14.

Before its approval, several questions regarding the safety of BST, in particular its effects on human health and nutrition, were critically examined 14. These related to the presence of BST residues in milk and the effect of BST on milk’s nutrient composition.

BST is naturally present in trace amounts in milk (i.e., 1 to 10 ng per ml) from untreated cows 9-14. Independent studies of BST carried out by the FDA, state agricultural departments, some pharmaceutical companies, and scientists found that milk from cows supplemented with BST contained no more BST than other milks 9-14.

BST has been proven safe for human health. The FDA (in a critical review of more than 120 studies) 10, scientists from Washington University School of Medicine in St. Louis and Cornell University in Ithaca, NY 11, a National Institutes of Health Technology Assessment Panel 12, the Office of Technology Assessment 13, the American Council on Science and Health 15, and a commentary in the journal, Pediatrics 16, along with regulatory agencies worldwide, have independently concluded that dairy foods from BST-treated cows are safe for human consumption.

There are several reasons why BST residues in milk, present either naturally or as a result of BST administration to cows, do not have any physiological effect on humans ingesting the milk 9-14. BST is species-specific, which means that BST is biologically inactive in humans, even if injected 10, 11, 14, 16. Also, pasteurization destroys 90% of BST in milk 10, 12. Furthermore, any trace amounts of BST ingested in milk are broken down into inactive fragments (i.e., constituent amino acids) by enzymes in the gastrointestinal tract, just like any other protein 10-12.

Although a protein controlled by BST (i.e., insulin-like growth factor I or IGF-I) is slightly elevated in the milk of BST-treated cows, data indicate that IGF-I levels in milk from BST-treated cows are within normal range and are lower than levels reported in human milk 10-12. Moreover, in animal studies, this protein is not toxic, even in high doses 10,14. Like all other dietary proteins, Like all other dietary proteins, IGF-I is broken down by enzymes in the digestive tract prior to absorption. Therefore, IGF-I consumed in foods has no biological activity in humans.

Administering BST to cows does not significantly change milk composition or nutritional quality 10, 11, 14. Any minor differences in milk composition reported between BST-supplemented and BST-unsupplemented cows are within the normal biological ranges 10, 11. Because there are no differences in milk from BST-treated cows and milk for cows not treated with this hormone, dairy products from cows treated with BST are not required to be labeled at such 8.

Critics of BST purport that BST increases a cow’s risk of mastitis (udder inflammation), thereby exposing milk drinkers to additional animal antibiotics used in treatment. However, an FDA advisory committee concluded that other factors (e.g., season, age of the cows) are more likely than BST to be associated with mastitis 17. Moreover, FDA has established safeguards to prevent unsafe levels of antibiotic residues from entering the milk supply 17.

FDA is not authorized to require special labeling for milk from BST-treated cows. However, food companies that do not use milk from cows supplemented with BST can voluntarily label their products with this information. To help ensure that consumers are not misled, FDA issued interim guidelines on February 8, 1994, for the voluntary labeling of milk from cows that have not been treated with BST 18. According to these guidelines, labels for dairy foods can state that the foods come from "cows not treated with" the hormone. However, the label would also have to carry an accompanying statement such as "No significant difference has been shown between milk derived from rbst-treated and non-rbst treated cows" 18.

The FDA has recently reaffirmed its 1993 position that milk from cows treated with BST is safe for human consumption 19. Likewise, the Joint FAO/WHO Expert Committee on Food Additives recently reconfirmed its 1992 position on the safety of BST 20.

References for Hormones and Milk

1. Jenness, R. Composition of milk. In: Fundamentals of Dairy Chemistry. 3rd ed. N. P. Wong, R. Jenness,

M. Kenney, and E.H. Marth (Eds.). New York: Van Nostrand Reinhold Co., 1988, p.19.

2. Campana, W. M., and C. R. Baumrucker. Hormones and growth factors in bovine milk. In: Handbook of Milk Composition. R.G. Jensen (Ed.). New York: Academic Press, 1995, pp. 476-494.

3. Koldovsky, O., and W. Thornburg. Hormones in milk. J. Pediatr. Gastroenterol. Nutr. 6: 172-196. 1987.

4. Gyawu, P., and G. S. Pope. Oestrogens in milk. J. Steroid Biochem. 19: 877-882, 1983.

5. Hagemeister, H., H. Sick, and C. A. Barth. Nitrogen balance in the human and effects of milk constituents. Role of Milk Protein in Human Nutrition. Bull. Int. Dairy Federation 253: 3-18, 1990.

6. Collins, S. S., K. E. Belk, H. R. Cross, and G. C. Smith. The EEC ban against growth-promoting hormones. Nutr. Rev. 47: 238-246, 1989.

7. Kenney, J., and D. Fallert. Livestock hormones in the United States. Natl. Food Rev. 12: 21-24, 1989.

8. Food and Drug Administration, USDHHS. Animal drugs, feeds, and related products; sterile sometribove zinc suspension. Fed. Regist. 58(217): 59946-47, 1993.

9. Blayney, D. P. Milk and biotechnology: maintaining safe, adequate milk supplies. Food Rev. 17(2):27-31, 1994.

10. Juskevich, J. C., and C. G. Guyer. Bovine growth hormone: human food safety evaluation. Science 249:875-884, 1990.

11. Doughaday, W. H., and D. M. Barbano. Bovine somatotropin supplementation of dairy cows. Is the milk safe? JAMA 264: 1003-1005, 1990.

12. Technology Assessment Panel. NIH Technology Assessment Conference statement on bovine somatotropin. JAMA 265: 1423-1425, 1991. (Nutr. Rev. 49: 227-232, 1991).

13. U.S. Congress, Office of Technology Assessment, U.S. Dairy Industry at a Crossroad: Biotechnology and Policy Choices: Special Report. OTA-F-470. Washington, DC: Superintendent of Documents, U.S. Government Printing Office, May 1991.

14. Etherton, T. D., P. M. Kris-Etherton, and E. W. Mills. Recombinant bovine and porcine somatotropin: safety and benefits of these biotechnologies. J. Am. Diet. Assoc. 93: 177-180, 1993.

15. American Council of Science and Health. BST=A Safe, More Plentiful Milk Supply. September 1990.

16. Kretchmer, N. Why not have more milk? Pediatrics 88: 1056-1057, 1991.

17. Ropp, K. L. New animal drug increases milk production. FDA Consumer 28(4): 24-27, 1994.

18. Food and Drug Administration. Interim guidance on the voluntary labeling of milk and milk products from cows that have not been treated with recombinant bovine somatotropin. Fed. Regist. 59(Feb 10):

19. Report on the Food and Drug Administration’s Review of the Safety of Recombinant Bovine Somatotropin.

20. Murphy, J. JECFA approves safety of BST; report forwarded to Codex. Food Chemical News 40(4):




A review of the hormone prolactin during lactation.

Ostrom KM

Department of Nutritional Sciences, University of Connecticut, Storrs.

The principal lactogenic hormone, prolactin, secreted by the anterior pituitary is critical to the establishment of lactation, milk macronutrient content and milk production. The concentration of circulating prolactin increases during pregnancy so that by the end of gestation, levels are 10 to 20 times over normal amounts. However, prolactin is prevented from exerting its effect on milk secretion by elevated levels of progesterone. Following clearance of progesterone and estrogen at parturition, copious milk secretion begins. The minimal hormonal requirements for normal lactation to occur are prolactin, insulin and hydrocortisone. Prolactin stabilizes and promotes transcription of casein mRNA; may stimulate synthesis of alpha-lactalbumin, the regulatory protein of the lactose synthetase enzyme system; and increases lipoprotein lipase activity in the mammary gland. Prolactin levels decrease as lactation is established but nursing stimulates prolactin release from the pituitary which promotes continued milk production. Prolactin is secreted into milk at levels representative of the average circulating concentration. The physiological significance of milk prolactin to the infant is uncertain. Prolactin exists in three heterogenic forms which possess varying biological activity. The monomer with a molecular weight of 23 kDa is found in greatest quantity and is the principal biologically active form. The pattern of heterogeneity changes during pregnancy to favor even more monomer in proportion to the dimer. However, during lactation, the proportion of the monomer in circulation decreases in response to selective uptake of the monomer by the mammary gland. Over 90 percent of the prolactin in milk is present as the monomer. Prolactin may exert some of its biological effect by a shift in the ratio of active to less active forms of the molecule.

Med Hypotheses 1997 Jun;48(6):453-61 t


Dairy products and breast cancer: the IGF-I, estrogen, and bGH hypothesis.

Outwater JL, Nicholson A, Barnard N

A. B. Princeton University 1996, Physicians Committee For Responsible Medicine, Washington, DC 20016, USA.

Research on the role of dietary factors in breast cancer causation has focused predominantly on fat intake. While some studies have examined associations between breast cancer rates and consumption of whole milk, there has been less attention given to dairy products in general. Dairy products contain both hormones and growth factors, in addition to fat and various chemical contaminants, that have been implicated in the proliferation of human breast cancer cells. This literature review evaluates the epidemiological and mechanistic evidence linking dairy consumption with breast cancer risk.

Hormones (estrogens) are also involved in cancers of reproductive organs, like breast and uterine cancer. There are several reasons dairy products raise a woman's hormone levels causing a variety of hormone-dependent problems from early onset of menstruation (menarche) to PMS and uterine fibroids - but one is unique to cow's milk. Cows are milked even while they are pregnant. As a result of the pregnancy, cows secrete high levels of estrogen into their milk.