有没有给奶牛添加生长激素？

在北美，经常可以看到为乳腺癌的慈善募捐活动，也看到一些名人得前列腺癌报道，乳腺癌和前列腺癌的发病率比较高，到底为什么原因？不清楚。听说北美给奶牛添加生长激素，而过多的生长激素与这二种癌症有可能有关。我查了一下百度百科和维基百科，在美国，是允许给奶牛用生长激素的，但是否致癌没有定论。

摘自《百度百科》-----牛奶

牛奶营养丰富，每天喝牛奶的人越来越多，但有许多研究发现，常喝牛奶的男性易患前列腺癌。前列腺癌是男性生殖系统常见的恶性肿瘤，美国波士顿一研究小组对20885例美国男性医师进行了长达11年的随访调查，食用的奶制品主要包括脱脂奶、全脂奶和乳酪等，其中有1012例男性发生前列腺癌。

在排除了年龄、体重、吸烟、体育锻炼等影响因素后发现，每天进食奶制品2.5份以上(每份相当于240ml牛奶)的男性与进食奶制品0.5份以下的相比，发生前列腺癌的危险上升34％。美国费城的研究人员通过近10年的流行病学调查也证实，多食奶制品会增加男性发生前列腺癌的危险。

摘自《维基百科》From Wikipedia, the free encyclopedia------milk

Bovine growth hormone supplementation

Since November 1993, with FDA approval,[70] Monsanto has been selling recombinant bovine somatotropin (rbST), also called rBGH, to dairy farmers. Cows produce bovine growth hormone naturally, but some producers administer an additional recombinant version of BGH which is produced through a genetically engineered E. coli because it increases milk production. Bovine growth hormone also stimulates liver production of insulin-like growth factor 1 (IGF1). Monsanto has stated that both of these compounds are harmless given the levels found in milk and the effects of pasteurization,[71] however, Monsanto's own tests, conducted in 1987, demonstrated that statistically significant growth stimulating effects were induced in organs of adult rats by feeding IGF-1 at low dose levels for only two weeks. "Drinking rBGH milk would thus be expected to significantly increase IGF-1 blood levels and consequently to increase risks of developing breast cancer and promoting its invasiveness."[72]

On June 9, 2006, the largest milk processor in the world and the two largest supermarkets in the United States--Dean Foods, Wal-Mart, andKroger--announced that they are "on a nationwide search for rBGH-free milk."[73] Milk from cows given rBST may be sold in the United States, and the FDA stated that no significant difference has been shown between milk derived from rBST-treated and that from non-rBST-treated cows.[74] Milk that advertises that it comes from cows not treated with rBST, is required to state this finding on its label.

Cows receiving rBGH supplements may more frequently contract an udder infection known as mastitis.[75] Problems with mastitis have led to Canada, Australia, New Zealand, and Japan banning milk from rBST treated cows. Mastitis, among other diseases, may be responsible for the fact that levels of white blood cells in milk vary naturally.[76][77]

In the European Union, rBGH is banned.[78]