Numerous studies have found that the milk consumption is related to lower risk of colon cancer and that this relationship appears to be due in part to the calcium found in milk. However, studies also indicate that the consumption of milk may increase the risk of developing prostate, endometrial, testicular and ovarian cancer, although some of the relative risks do not appear to be high. Whole milk is a source of saturated fat, which has been linked to cardiovascular disease as well as various cancers.
Breast cancer-related effects of drinking milk
Many studies have been conducted to try to determine the effects of milk consumption on the risk of breast cancer and on breast cancer development, but the results appear contradictory, presumably because milk has both beneficial and harmful components.
Components of milk, including calcium, vitamin D, stearate, lactaptin, conjugated linoleic acid (CLA), and bovine lactoferricin, have been found to induce apoptosis of breast cancer cells or reduce mammary tumor size and incidence in the laboratory. In fact, milk has been found to be somewhat protective against breast cancer when consumed in infancy and childhood.
Some population-based studies have found that milk consumption is not associated with risk of breast cancer. However, the case against consuming milk in adulthood is compelling, on balance. One study of rats with carcinogen-induced mammary tumors found that while removing the ovaries of rats reduced the number and size of the tumors, feeding milk to similar ovariectomized rats led to increases in mammary tumor incidence, tumor number and tumor volume. Consumption of both nonfat and whole milk also has been found to increase the incidence and volume of tumors in experimental rats with carcinogen-induced mammary tumors. Several major population-based studies have found that milk consumption is positively associated with the risk of breast cancer. High intake of animal fats has been linked in several studies to increased breast density, a risk factor for breast cancer and recurrence.
Several studies have reported that bovine leukemia virus, which is prevalent in U.S. dairy herds, could contribute to human breast cancer. Most women carry BLV antibodies in their blood, indicating exposure to the virus. The most likely sources of BLV exposure are raw milk and raw or rare beef, which should be avoided. One 2015 study reported that women with BLV in their breast tissue were three times as likely to have breast cancer as women without BLV. Pasteurization destroys the virus. Raw milk labelled "organic" is not necessarily BLV-free.
Some observers have noted that much of the milk we drink today is produced from pregnant cows, in which estrogen and progesterone levels are markedly elevated. Other components of milk that are suspected to be breast cancer promoting include saturated fat, recombinant bovine growth hormone (rBGH), insulin-like growth factor (IGF), pesticides, and polychlorinated biphenyls (PCBs). Since cream concentrates some of the potentially harmful substances found in milk, it is also to be avoided.
Since calcium and vitamin D both have been shown to be very significant in protecting against cancer, and since milk is a major source of both in the typical American diet, it is important that those who start to limit their consumption of milk add new sources of calcium and vitamin D.
Consuming unpasteurized or raw milk is associated with health hazards due to possible contamination with pathogenic bacteria, in addition to bovine leukemia virus.
Kefir, a fermented milk drink, has been found to be associated with reduced breast cancer risk.
Below are links to recent studies concerning this food. For a more complete list, including less recent studies, please click on milk.