Impact of cows’ milk estrogen on cancer risk

Estrogens have been implicated in cancer at hormone-responsive sites, such as the breast, ovaries, endometrium and prostate. Because cows’ milk contains estrogens, some authors have suggested that its consumption may contribute to the risk of cancer at these sites. However, these reports do not recognize the complex mechanisms these cells possess to regulate estradiol levels. Hormone-responsive and many peripheral cells contain all the necessary steroidogenic enzymes necessary for in situ synthesis of bioactive estradiol from abundant androgenic precursors and for inactivation of unwanted estrogens. Estradiol from dairy products is extensively inactivated in the gastrointestinal tract and only about 5% survives the first pass to the liver. Thus daily dairy product intake would supply only about 0.25% of the FAO/WHO upper acceptable daily intake of estradiol. Available epidemiological evidence does not suggest an association between dairy product consumption and risk of cancer of the breast, ovaries and endometrium.