Is Milk from rbGH-Injected Cows Safe? Why Isn\'t It Labeled?Response:
Bovine growth hormone (bGH), also called bovine somatotropin (bST), is unrelated to steroid hormones. bGH, produced in the pituitary glands of dairy cows, is a naturally occurring protein hormone in milk, which stimulates the liver to produce insulin-like growth factor-I (IGF-I). The structure of human somatotropin differs from bGH, and the latter is not biologically active in humans (1). Upon pasteurization, 90% of bGH is destroyed; digestive enzymes degrade the remainder. Other growth factors in milk (e.g., the cytokines IL-1 and IL-2), though sometimes slightly elevated in milk from bGH injected cows, are inactive in other mammals (2).
Since the late 1920s it was known that lactating mammals produce more milk when treated with extracts of the pituitary hormone bGH, but because that hormone could only be isolated from the pituitary glands of slaughtered cattle, bGH was not available in sufficient quantities for commercial use in the dairy industry (3). Sufficient quantities were made available when a synthetic gene for bGH was inserted into a bacterium to produce recombinant bGH (rbGH or rbST), which is chemically identical to bGH. When rbGH is injected into cows, the efficiency of conversion of feed to milk is increased and milk yields can be increased by 15% to 20% (4, 5). Trace amounts of bGH is found in all milk; cows given rbGH contain no morebGH than unsupplemented cows (2). Published data indicate that the use of rbGH to increase milk production does not impact its nutritional quality.
Extensive studies of rbGH safety have been conducted worldwide and reviewed by the FDA, after which both milk and meat from rbGH-injected cows were deemed safe (6). Separate reviews of the data by the National Institutes of Health, theWorld Health Organization, the Office of the Inspector General of the Department of Health and Human Services, and reviews by the Journal of the American Medical Association and the Journal of the American Dietetic Association all independently concluded that milk from rbGH injected cows is safe.
Despite these safety assurances, claims were made as recently as 2001 (7) that milk from rbGH-treated cows contains elevated levels of IGF-I, a protein hormone normally present in milk (8). An elevated content of IGF-I has been suggested to have adverse implications for human health and cancer frequency. Comparisons of marketed milk indicate that there are no differences in IGFI concentrations between milk derived from cows treated or not with rbGH (9), and levels are within the limits of natural variation (for review, see 10). Assumptions that milk levels of IGF-I increase after cows are treated with rbGH and that biologically active IGF-I is absorbed into the body are not supported by the main body of science (10). Carefully analyzing published literature provides no compelling evidence that milk from rbGH-treated cows contains higher levels of IGF-1 compared to milk from untreated cows. Although some studies claim that milk proteins protect IGF-I from digestion, the vast majority of published evidence indicates that very little IGF-I is absorbed following ingestion. IGF-I content of milk from rbGH-treated cows has been extensively reviewed and its safety confirmed (6, 11, 9).
The FDA concluded that the use of rbGH in dairy cattle presents no confirmed health risks to consumers and the milk is substantially equivalent to milk from cows not treated with rbGH (see “Are Food Safety Studies Conducted on GE Foods?”). However, aside from safety issues, some consumers view the use of rbGH to increase milk production as “unnatural” and this has been promoted as a reason to oppose milk from cows injected with rbGH (3). This perspective led some dairies to voluntarily, although not legally, label milk as being from cows not injected with rbGH, even though FDA labeling policy for foods produced from GE ingredients (which is the same as for all other foods and food ingredients) specifies no label is needed if the food is substantially equivalent to non-GE foods in safety, composition, and nutrition. Of note, in January 2008, the Pennsylvania Department of Agriculture issued a new labeling standard indicating that milk could be labeled as coming from cows not treated with rbGH as long as the labeling was uniform (12).
Outside the U.S., countries that are signatories to the World Trade Organization cannot bar milk from cows injected with rbGH based solely on its production method, unless there is scientific evidence that it affects human health or safety (3). But the E.U. has been staunch in its opposition to such milk in part due to consumer concerns that arose in the 1990s as a result of certain food safety outbreaks, such as bovine spongiform encephalopathy (13), that were not effectively handled by existing regulatory systems. In 1999 the E.U. decided not to approve sales of milk from rbGH-treated cows in E.U. member countries, based not on human health concerns but on animal welfare issues (14). Today milk and milk products from rbGH-treated cows are recognized as safe in the E.U. and can be marketed in E.U. countries (15, 11), but the use of rbST in their dairy herds is not approved.
With regard to animal health, some studies have reported an increased frequency of mastitis in groups of rbGH-treated cows. This increase has been attributed mainly to increased milk volume in the mammary glands of treated cows and no convincing data are available that show a decrease in secretion of mammary gland immune factors as a result of growth hormone treatments (16). A 1999 study (17) indicated the rbGH can actually provide a protective effect against Streptococcus uberis mastitis following experimental infection.
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