In 1997, the World Cancer Research Fund and the American Institute for Cancer Research concluded that dairy products should be considered a possible contributor to prostate cancer. Researchers are looking, not only at whether milk increases cancer risk, but how . The answer, apparently, is in the way milk affects a man's hormones. In turn, IGF-I promotes cancer cell growth. A small amount is normally in the bloodstream, but several recent studies have linked increased IGF-I levels to prostate cancer and possibly to breast cancer as well.
Milk does other mischief.
Its load of calcium depletes the body's vitamin D, which, in turn, may add to cancer risk. Most dairy products are also high in fat, which affects the activity of sex hormones that play a major role in cancer. And it would come as no surprise that milk might affect the growth of cancer cells. After all, its biological purpose is to support rapid growth in all parts of a calf's body. Researchers are investigating whether dairy products might be culprits in other forms of the disease.