这是一个有争议的问题，不妨参看美国乳腺癌基金会的评论

争议的焦点是牛奶中的insulin-like growth factor 1 (IGF-1，类胰岛素生长因子-1) 。乳癌基金会的评论说：

“Elevated levels of IGF-1, in particular, have been associated with increased risk of breast cancer (Hankinson, 1998). Proponents of rBST argue that IGF-1 is harmless because it occurs naturally in humans, is contained in human saliva and is broken down during digestion. However, animal evidence indicates that digestion does not break down IGF-1 in milk because casein, the principal protein in cow’s milk, protects IGF-1 from the action of digestive enzymes (Xian, 1995).”

翻译如下：

“尤其是（奶中）增加的IGF-1, 与乳腺癌的风险有关 (见：Hankinson, 1998)。使用牛生长激素的赞成者争辩说，IGF-1 是无害的，因为它本来就天然地存在于人体，在人的唾液中就有，经过消化道时被降解。可是，有动物证据显示，消化过程不能降解牛奶中的 IGF-1，原因在于奶中的酪蛋白（casein）。酪蛋白是牛奶中的主要蛋白成分，它能保护lGF-1 不受消化酶的作用 (见 Xian, 1995)。”

 乳癌基金会评论链接：

http://www.breastcancerfund.org/clear-science/radiation-chemicals-and-breast-cancer/bovine-growth-hormone.html