Many studies have been conducted to try to determine the effects of milk consumption on the risk of breast cancer and its recurrence. The results are somewhat inconsistent. Milk is a complex food that incorporates both anti-cancer and cancer-promoting compounds. However, on balance, full-fat milk appears to promote breast cancer and its progression.
Numerous studies have reported that milk (i.e., cow's milk) consumption is related to lower risk of colon cancer (a relationship that appears to be due in part to the calcium found in milk). However, studies also indicate that milk consumption may increase the risk of prostate, endometrial, testicular and ovarian cancer, although some of the increases appear to be modest.

Breast cancer-related effects of drinking milk

Anti-breast cancer milk components

Milk is a very good source of conjugated linoleic acid (CLA), bovine lactoferrin, and lactaptin. Each of these compounds has been reported to induce apoptosis of breast cancer cells or reduce mammary tumor size and incidence in the laboratory.
For example, CLA, a fatty acid found primarily in dairy foods and meat, has been demonstrated to inhibit the growth of both estrogen receptor positive (ER+) and estrogen receptor negative (ER-) breast cancer cells. CLA has also been reported to alter estrogen receptor transcriptional activities and inhibit cancer cell adhesion and migration. However, potentially beneficial effects of the CLA in milk appear to be overwhelmed by its cancer-promoting characteristics. One 2022 study reported that CLA from ruminant sources was associated with increased breast cancer risk.
Milk is also a source of other compounds such as calcium, iodine, riboflavin (vitamin B2), stearate, vitamin B12 and vitamin D that have demonstrated or suspected anti-cancer activities.
Note that fermented milk, which is covered in the kefir webpage, has been found to be associated with reduced breast cancer risk.

Breast cancer-promoting milk components

Whole milk has an unfavorable fat profile
Whole milk is a source of several types of saturated fat, as well as cholesterol, all of which have been found to be associated with increased breast cancer risk. The saturated fatty acids in milk (primarily palmitic acid, myristic acid, and stearic acid) account for approximately 70% by weight. Myristic acid has been linked to increased breast cancer risk in epidemiological studies. Intake of animal fats has been found to be associated in several studies to increased breast density, a risk factor for breast cancer and its recurrence. High cholesterol has been shown to promote metastasis in an animal model of breast cancer.
Milk production methods can be source of harmful compounds
Most of the milk we drink is produced from pregnant cows, in which estrogen and progesterone levels are markedly elevated, although the effect on breast cancer risk is not clear. Other components of milk influenced by milk production methods that are suspected to be breast cancer promoting include 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 to be avoided.
Raw milk is potential source of bovine leukemia virus
Several studies have reported that bovine leukemia virus (BLV), which is prevalent in U.S. dairy herds, could contribute to breast cancer risk, although not all studies are in agreement. One study found that women with BLV in their breast tissue were three times as likely to have breast cancer as women without BLV. Most women carry BLV antibodies in their blood, indicating exposure to the virus.
The most likely sources of BLV exposure are raw or rare beef and raw (unpasteurized) milk. A 2020 Brazilian study reported that women who consumed raw milk had high rates of BLV DNA in breast tissue samples. Breast cancer patients living in a region of Brazil where unpasteurized dairy products are normally consumed were found to have higher rates (96%) of BLV than healthy women (59%).
Raw milk labelled "organic" is not necessarily BLV-free. Pasteurization destroys this virus (as well as bird flu virus, which has been shown to be prevalent in US dairy herds as of early 2024). Note that raw milk has also been linked to foodborne illnesses due to contamination with pathogenic bacteria.

Animal studies of milk consumption

A 2021 study that compared calorically equivalent milk and olive oil high-fat diets in a mouse model of breast cancer reported that animals in the olive oil group developed a lower number of lung metastases with a decreased surface area compared to the milk group. The authors concluded that different types of fats predominating in high-fat diets might have varying influences on breast cancer metastasis.
Another 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 have also been found to increase the incidence and volume of mammary tumors in experimental rats with carcinogen-induced tumors.

Human studies

Since milk incorporates both beneficial and potentially harmful compounds, it makes sense to look to the actual effects of milk consumption to determine whether it prevents or promotes breast cancer and its progression. Although some population-based studies have reported that milk is not associated with breast cancer risk, on balance there is enough evidence to caution against consuming milk in adolescence and adulthood:
  • A major 2023 prospective study reported that milk intake, including adolescent milk intake, was modestly associated with higher breast cancer risk. The positive association appeared stronger for postmenopausal breast cancer.
  • A 2023 analysis of available research concluded that commercial milk consumption is an important risk factor for ER+ breast cancer. Milk also appears to be linked to increased breast cancer risk in BRCA1 carriers.
  • A 2021 meta-analysis of data from previous studies with a total of 1,019,232 participants reported that high-fat dairy was associated with increased breast cancer risk in both premenopausal and postmenopausal women.
  • A major 2021 prospective Chinese study found that dairy consumption (with milk accounting for most of this) was associated with increased breast cancer risk.
  • A 2021 meta-analysis of data from previous studies found no clear association between milk consumption and risk of breast cancer.
  • A large 2021 prospective study of Spanish women found an inverse association between intermediate low-fat dairy product consumption and premenopausal breast cancer, as well as between medium total dairy product consumption and postmenopausal breast cancer.
  • A major 2020 Swedish study reported that normal and underweight women who had long-term milk consumption of at least two servings of milk per day experienced a higher risk of breast cancer than those with lower milk intake.
  • A 2019 study of 52,795 women in the Adventist Health Study-2 (AHS-2) cohort determined that dairy milk consumption was clearly associated with increased breast cancer risk.
  • A 2013 prospective study including 1,893 women with early-stage breast cancer reported that those consuming greater amounts of high-fat (but not low-fat) dairy had higher rates of breast cancer-specific mortality.
Note that milk has been found to be somewhat protective against breast cancer when consumed in infancy and childhood. Milk should not be withheld from infants and children in an attempt to prevent breast cancer.

Best milk for those with breast cancer

While we do not recommend milk, modest amounts consumed infrequently may not be harmful. Based on the available evidence, the best choice appears to be organic, pasteurized, skim or low-fat, grass-fed milk.

Additional comments

Milk contains important nutrients
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.
Sugar in chocolate milk outweighs benefits of chocolate content
Chocolate milk incorporates some of the polyphenols with anti-cancer properties found in chocolate, including catechin, epicatechin and procyanidins. However, the amounts are small and any potential benefits are likely to be offset by the added sugar content of chocolate milk. Chocolate milk brands that list carrageenan (a thickener that is a possible breast carcinogen) as an ingredient should be avoided.
Benefits of grass-fed milk
Milk from grass-fed cows has a higher level of CLA, vitamin B12 and some other nutrients than than milk from cows fed primarily grain. Grass-fed milk also incorporates less saturated fat and has a more favorable omega-6 to omega-3 fatty acid profile (with a lower level of omega-6 and a higher level of omega-3 fats), although this difference may not be meaningful in the content of the relatively high-fat U.S. diet. To the extent that grass-fed cattle are not fed soy products, grass-fed milk also prevents exposure to the estrogenic isoflavone content potentially contributed by soy in conventional milk.

Sources of information provided in this webpage

The information above, which is updated continually as new research becomes available, has been developed based solely on the results of academic studies. Clicking on any of the underlined terms will take you to its tag or webpage, which contain more extensive information.
Below are links to 20 recent studies concerning this food and its components. For a more complete list, including less recent studies, please click on milk.