Milk is not recommended for breast cancer
Numerous studies have found that the consumption of milk is related to lower risk of colon cancer and that this relationship appears to be due in part to the calcium found in milk. 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.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, 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.
Several major population-based studies have found that milk consumption is not associated with risk of breast cancer. However, the case against consuming milk in adulthood appears to be compelling. 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. A 2007 study found that bovine leukemia virus, which is prevalent in U.S. dairy herds, could contribute to human breast cancer. 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, pesticides, and polychlorinated biphenyls. Since cream concentrates some of the potentially harmful substnaces found in milk, it is also to be avoided.
Additional comments
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.
Although consuming unpasteurized milk is associated with health hazards due to possible contamination with pathogenic bacteria, it does not appear to increase the risk of cancer. Kefir, a fermented milk drink, has been found to be negatively associated with breast cancer risk.
Selected studies
Prepubertal exposure to cow's milk reduces susceptibility to carcinogen-induced mammary tumorigenesis in rats International Journal of Cancer, March 2010The present study was designed to investigate whether prepubertal cow's milk exposure affects mammary gland development and carcinogenesis in rats. Milk contains high levels of estrogens, progesterone and insulin-like growth factor 1 (IGF-1), all of which have been reported to be associated with increased risk of breast cancer. In the study, Sprague-Dawley rats were given either whole milk or tap water to drink from day 14 to day 35 after birth; all of the rats received tap water thereafter. Mammary tumors were induced by administering the carcinogen 7,12-dimethylbenz[a]anthracene on day 50. Milk exposure was found to increase circulating estradiol (E2) levels 10-fold (p < 0.001) by day 25. Milk consumption also accelerated vaginal opening, which marks the onset of puberty in rats, by 2.5 days (p < 0.001). However, rats fed milk before puberty were found to have reduced mammary carcinogenesis: tumor latency was longer (p < 0.03) and incidence was lower (p < 0.05) than in the water-fed controls. Mammary glands of milk-exposed rats had significantly fewer terminal end buds than controls (p < 0.019) when sampled on days 25 and 50. Estrogen receptor protein levels were elevated in the terminal end buds and lobules of milk-fed rats, compared to controls (p < 0.019), but no changes in cyclin D1 expression, cell proliferation or apoptosis were observed. IGF-1 mRNA levels were found to be reduced on day 50 in the mammary glands of rats exposed to milk at puberty. The authors conclude that consuming milk before puberty reduces later risk of developing mammary cancer in rats. This reduced risk might be mediated by a reduction in the number of terminal end buds and lower expression of IGF-1 mRNA in the mammary glands of milk-exposed animals.
Conjugated linoleic acid intake and breast cancer risk in a prospective cohort of Swedish women American Journal of Clinical Nutrition, September 2009
The present prospective study was designed to investigate the association between intake of conjugated linoleic acids (CLAs) and the risk of breast cancer. Animal and in vitro studies suggest that CLAs, fatty acids found primarily in dairy products and in the meat of ruminants, have protective activities against mammary carcinogenesis. However, findings from population studies in relation to breast cancer risk are few and inconsistent. The study included 61,433 women in the Swedish Mammography Cohort who were cancer-free at enrollment during 1987 to 1990. Dietary CLA intake was determined by means of a food-frequency questionnaire at baseline. Cox proportional hazards models were used to calculate rate ratios (RRs) and 95% confidence intervals (CIs), adjusted for breast cancer risk factors. During a mean follow-up period of 17.4 years, 2,952 new cases of invasive breast cancer were diagnosed in the study group. No significant association was found between dietary CLA intake and risk of breast cancer, overall or by estrogen receptor (ER) and progesterone receptor (PR) status of the tumors. The multivariate relative risks (95% CI) for the highest fifth of CLA intake (155.7 mg/day) compared with the lowest quintile (<78.1 mg/day) were 1.04 (0.92 - 1.17) for overall breast cancer, 1.09 (0.90 - 1.31) for ER+/PR+ tumors, 1.09 (0.78 - 1.53) for ER+/PR- tumors, and 0.84 (0.57 - 1.24) for ER-/PR- tumors. The authors conclude that the results provide no evidence of a protective effect of CLA against breast cancer development in women.
Meat, eggs, dairy products, and risk of breast cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort American Journal of Clinical Nutrition, June 2009
The present prospective study was designed to investigate the association between meat, egg, and dairy product consumption and risk of breast cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC) study cohort. Information concerning diet was collected from 319,826 women during the period 1992 - 2003. During a median follow-up period of 8.8 years, 7,119 breast cancer cases were diagnosed. Multivariate Cox proportional hazard models were used to calculate disease hazard ratios. No consistent overall association was found between risk of breast cancer and consumption of any of the food groups under study. High consumption of processed meat was associated with a modest increase in breast cancer risk in the categorical model (hazard ratio: 1.10; 95% CI: 1.00 - 1.20; highest versus with lowest quintile: P for trend = 0.07). An association of breast cancer risk with butter consumption for premenopausal women was suggested in subgroup analysis (hazard ratio: 1.28; 95% CI: 1.06 - 1.53; highest compared with lowest quintile: P for trend = 0.21). Between-country heterogeneity was found for red meat consumption (Q statistic = 18.03; P = 0.05) and was significantly explained by the proportion of meat cooked at high temperature (P = 0.023). The authors conclude that they had not consistently identified intakes of meat, eggs, or dairy products as risk factors for breast cancer.
Dairy food, calcium, and risk of cancer in the NIH-AARP diet and health study Archives of Internal Medicine, February 2009
In the present large prospective cohort study, researchers from the National Institute of Health’s Diet and Health Study set out to determine whether dairy food and calcium in the diet were associated with risk of various cancers, as well as total cancer. A food frequency questionnaire was used to measure intakes of dairy food and calcium from foods and supplements. State cancer registries were used to identify new cancer cases during the follow-up period. During an average of seven years of follow-up, 36,965 male and 16,605 female cancer cases were identified. In both men and women, dairy food and calcium intakes were found to be inversely associated with cancers of the digestive system. Dairy food, dietary calcium, supplemental calcium, and total calcium were not associated with total cancer mortality for both men (8,787 deaths) and women (4,479 deaths). The researchers also found that in women, total calcium intake was not linearly associated with total cancer incidence: the risk decreased up to approximately 1300 mg of calcium per day, after which no further risk reduction was gained by consuming more calcium.
Long-term dietary calcium intake and breast cancer risk in a prospective cohort of women American Journal of Clinical Nutrition, January 2009
The current prospective study was designed to examine the association between dietary calcium intake and breast cancer risk by estrogen receptor (ER) and progesterone receptor (PR) status of the tumor. Calcium is thought to potentially influence breast cancer risk since it has a role in regulating cell proliferation, differentiation, and apoptosis. The study included 61,433 women in the Swedish Mammography Cohort who were cancer-free at enrollment during 1987 to 1990. Dietary calcium intake was determined by means of a food-frequency questionnaire at baseline and again in 1997. Cox proportional hazards models were used to calculate rate ratios (RRs) and 95% confidence intervals (CIs), adjusted for breast cancer risk factors. During a mean follow-up period of 17.4 years, 2,952 new cases of invasive breast cancer were diagnosed in the study group. Dietary calcium intake was found not to be associated with breast cancer risk in the group overall; the multivariate RR for the highest compared with the lowest fifth of calcium intake was 0.97 (95% CI: 0.87 - 1.09; P for trend: 0.49). However, a statistically significant inverse trend for ER-negative/PR-negative (ER-/PR-) breast cancer (P for trend: 0.02) was observed; the multivariate RR for the comparison of the highest with the lowest quintiles of calcium intake was 0.66 (95% CI: 0.44 - 0.99). Calcium intake was not found to be associated with ER+/PR+ or ER+/PR- tumors. The authors conclude that their findings do not support an association between dietary calcium intake and overall breast cancer risk and that the inverse relation between calcium intake and ER-/PR- breast cancer requires confirmation in other studies.
Unpasteurized milk consumption and subsequent risk of cancer Cancer Causes and Control, October 2008
The present study examined the relationship between self-reported intake of unpasteurized milk and subsequent risk of cancer using the Iowa Women’s Health Study cohort, with 55 to 69 year old women at baseline in 1986. 22,808 cancer-free women completed the fourth follow-up questionnaire in 1997. Reported intake of unpasteurized milk was relatively high: 59.2% consumed raw milk only as a child, 2.5% consumed it only as an adult, and 16.5% consumed it both as a child and as an adult. 2,379 cancers were found in the cohort at risk. The authors found that consumption of unpasteurized milk does not increase risk of cancer.
Milk Inhibits the Regression of 7,12-Dimethylbenz(a)anthracene-Induced Mammary Tumors in Ovariectomized Rats Nutrition and Cancer, July 2008
In the present study, the carcinogen 7,12-dimethylbenz(a)anthracene was used to induce mammary tumors in rats. After the tumors developed to pre-determined levels, the rats were divided into three treatment groups. The ovaries were removed from those in the negative control group and the milk group. Those in the positive control group were sham operated. After grouping, the tumor incidence stayed at 100% in each group. Both tumor number and tumor volume increased in the positive control group. However, the tumors in the two ovariectomized groups regressed, presumably because removing the ovaries depleted circulating estrogen. Compared with the negative control group, tumor incidence and tumor number and volume per rat in the milk group became significantly higher over time. Insulin-like growth factor-I levels were higher (with borderline significance) in the milk group than in the negative control group at autopsy. Although 17β-estradiol levels in the blood did not differ significantly between the milk group and the negative control group, estrogenicity was found in the milk group because uterine weight was significantly heavier than in the negative control group. The authors conclude that commercial milk inhibited the expected regression of existing mammary tumors in rats after removing the ovaries.
Bovine leukemia virus infection is significantly associated with risk of breast cancer American Association for Cancer Research (AACR) Meeting, April 2007
The present study was designed to investigate whether bovine leukemia virus is related to U.S. breast cancer risk. Breast cancer in mice can be caused by a retrovirus, mouse mammary tumor virus, which is transmitted from mother to nurslings. Since humans consume more cow milk than human milk, the authors were interested in determining if a bovine virus might be capable of causing human breast cancer. Bovine leukemia virus is an oncogenic retrovirus that infects more than 90% of U.S. dairy herds and more than 14% of beef herds. Fewer than five percent of infected cattle actually develop leukemia, resulting in their removal from the human food supply. The remaining infected cattle remain healthy and are sources of beef and dairy products. There is some evidence that humans can become infected with bovine leukemia virus. Previous studies have found IgG antibodies to bovine leukemia virus in 39% of study volunteers. Furthermore, bovine leukemia virus capsid protein and proviral DNA have been found in human mammary epithelium. In the current case-control study, 213 samples of formalin-fixed breast tissue sections from 110 women with breast cancer and 103 breast cancer-free controls were evaluated. The authors tested for the presence of bovine leukemia virus and found that positive reactions were present only in mammary epithelium. Bovine leukemia virus was found in 59% of the breast cancer cases and 29% of the controls. Adjusting for donor age, race, catchment area, and length of time in formalin-fixed state, the odds ratio for breast cancer associated with the presence of bovine leukemia virus was 3.22 (95% confidence interval = 1.7-6.2, P < .0005). The data indicates that 39% of the breast cancer cases were attributable to BLV infection. 69% of the specimens from women with breast cancer had bovine leukemia virus proviral DNA in accompanying nonmalignant mammary epithelium. This suggests that cancer development may have been a rare, delayed event within a population of bovine leukemia virus-infected cells widespread in the breast tissue. The authors conclude that the study is promising first step in establishing a causal role for bovine leukemia virus in human breast cancer.
The t10,c12 isomer of conjugated linoleic acid stimulates mammary tumorigenesis in transgenic mice over-expressing erbB2 in the mammary epithelium Carcinogenesis, January 2007
The present study was designed to test the efficacy of two conjugated linoleic acid (CLA) isomers in a clinically relevant breast cancer model. CLA has been shown to inhibit rat mammary carcinogenesis, angiogenesis, and lung metastasis from a transplantable mammary tumor. c9,t11-CLA, the predominant isomer in dairy products, and t10,c12-CLA, a component found in CLA supplements, have been found to be equally effective. Experimental erbB2 transgenic mice were fed either a control diet or a 0.5% CLA-supplemented diet after weaning. It was found that t10,c12-CLA unexpectedly stimulated lobular hyperplasia of the mammary epithelium and accelerated mammary tumor development. The t10,c12-CLA diet decreased median tumor latency to 168 days of age compared to 256 and 270 days in the c9,t11-CLA and control diet groups, respectively. Metastasis was also found to be increased by t10,c12-CLA, with the percentage of tumor-bearing mice with lung metastasis found to be 73%, 14% and 31% in the t10,c12-CLA, c9,t11-CLA and control groups, respectively. A second study was performed in which CLA administration was initiated after puberty. This study confirmed the cancer-promoting effect of t10,c12-CLA. In addition, t10,c12-CLA (but not c9,t11-CLA) increased the size of the mammary liver, heart, spleen and lymph node. The effects of t10,c12-CLA were not specific to the erbB2 transgenic mice, as t10,c12-CLA supplementation also increased proliferation in the mammary epithelium of wild-type FVB mice and FVB/erbB2 mice as well. In fact, the number of terminal end buds, the mammary epithelial structures most sensitive to a carcinogens, was increased 30-fold in FVB wild-type mice fed t10,c12-CLA. The authors conclude that it would be prudent to avoid CLA supplements containing the t10,c12-CLA isomer. However, even though c9,t11-CLA was not efficacious in the erbB2 model, its ability to inhibit mammary tumor development in some rat models suggests that it may have activity for prevention of some types of breast cancer.
Naturally Occurring Estrogens in Processed Milk and in Raw Milk (from Gestated Cows) Journal of Agricultural and Food Chemistry, November 2006
The occurrence of the steroid hormones estrone, 17α-estradiol, 17β-estradiol, and estriol in processed cow milk with different fat contents and in raw milk from non-gestating (i.e., not pregnant) cows was investigated. Estrone (6.2−1266 ng/L) was the major estrogen, followed by 17α-estradiol (7.2−322 ng/L) and 17β-estradiol (5.6−51 ng/L). Estriol was detected regularly at the detection limit of 10 ng/L. The lowest and highest concentrations of estrogens in raw milk were from nonpregnant cows and cows in the third trimester of gestation, respectively. The total estrogen concentration in processed milk coincides with that of raw milk from cows between the first and second trimesters of pregnancy, reflecting the contribution of lactating pregnant cows to the milk supply. The authors estimate the daily intake of total estrogens from milk at 372 ng, which is much more than currently recognized.
Dairy product consumption and the risk of breast cancer Journal of the American College of Nutrition, December 2005
This review starts with a brief overview of the roles of fat, bovine growth hormone, insulin-like growth factor-1, and estrogens and then examines the evidence from animal studies and epidemiology regarding the role of milk fat in the etiology of breast cancer. The daily intake of insulin-like growth factor-1 and biologically active estrogens from dairy products is minute in comparison to the daily endogenous secretion of these factors in women, and bovine growth hormone is biologically inactive in humans. On the other hand, milk contains rumenic acid, vaccenic acid, branched chain fatty acids, butyric acid, cysteine-rich whey proteins, calcium and vitamin D, all of which have the potential to help prevent breast cancer. Furthermore, the authors conclude, evidence from over 40 case-control studies and 12 cohort studies does not support an association between dairy product consumption and the risk of breast cancer.
Milk consumption in relation to incidence of prostate, breast, colon, and rectal cancers: is there an independent effect? Nutrition and Cancer, 2005 Vol. 53
The current study examined whether milk consumption is associated with the risk of prostate, breast, colon, and rectal cancers. Data on milk consumption for nine time periods during the period 1964 to 1994 and incidence rates of prostate, female breast, and colorectal cancers (mostly during 1993-1997) in 38 countries were collected from the Food and Agriculture Organization and the World Health Organization, respectively. Milk consumption was found to be strongly correlated with rates of prostate cancer and breast cancer for all nine time periods examined. A modest positive association was also found for colon and rectal cancers in both sexes. All of these findings remained essentially unchanged after adjustment for vegetable, alcohol, and cigarette consumption, but disappeared after further adjustment for fat consumption (i.e., other than milk fat consumption), except for breast cancer in the last three time periods.
Milk and lactose intakes and ovarian cancer risk in the Swedish Mammography Cohort American Journal of Clinical Nutrition, November 2004
The current prospective study was designed to examine the associations between consumption of dairy products and lactose and the risk of epithelial ovarian cancer and its subtypes. High dairy product consumption and high intake of the milk sugar lactose have been hypothesized to increase the risk of ovarian cancer, but prospective studies are scarce. The study comprised the 61,084 women aged 38 to 76 years who were enrolled in the Swedish Mammography Cohort. A self-administered food frequency questionnaire was used to gather dietary information in 1987-1990. During a mean follow-up period of 13.5 years, 266 women were diagnosed with invasive epithelial ovarian cancer; 125 of them had serous ovarian cancer. After adjusting for potential confounders, women who consumed at least four servings of total dairy products per day were found to have double the risk of serous ovarian cancer (rate ratio (RR) = 2.0; 95% confidence interval (CI): 1.1 - 3.7; P for trend = 0.06) than that of women who consumed fewer than two servings per day. No significant associations were observed for other subtypes of ovarian cancer. Milk had the strongest positive association with serous ovarian cancer (RR comparing consuming at least two glasses of milk per day with never or seldom consuming milk = 2.0; 95% CI: 1.1 - 3.7; P for trend = 0.04). A positive association between lactose intake and serous ovarian cancer risk was also observed (P for trend = 0.006). The authors conclude that high intakes of lactose and dairy products, particularly milk, are associated with an increased risk of serous ovarian cancer but not of other subtypes of ovarian cancer. Future studies should consider ovarian cancer subtypes separately.
Intake of conjugated linoleic acid, fat, and other fatty acids in relation to postmenopausal breast cancer: the Netherlands Cohort Study on Diet and Cancer American Journal of Clinical Nutrition, October 2002
Conjugated linoleic acid (CLA), which is present in milk and meat from ruminants, has been shown to have anticarcinogenic activity against breast cancer in animal and in vitro experiments. The present study was designed to evaluated the association between intakes of CLA and other fatty acids and the risk of breast cancer in the Netherlands Cohort Study. Information obtained by means of a validated 150-item food-frequency questionnaire was linked to an existing database with information on specific fatty acids in European foods. There were 941 new cases of breast cancer during a follow-up period of 6.3 years. Associations were calculated for energy-adjusted intakes of fatty acids and CLA-containing food groups (e.g., butter, cheese, milk, other milk products, and meat). CLA intake was found to have a weak, positive association with breast cancer incidence (rate ratio for highest compared with lowest quintile: 1.24, 95% CI: 0.91, 1.69; P for trend = 0.02). Statistically significant positive associations also were found with total trans fatty acids and with saturated fatty acids (borderline). Significant inverse relations were found with monounsaturated and cis-unsaturated fatty acids, whereas the total fat and energy intake of CLA-containing food groups were found not to be related to breast cancer incidence. The authors conclude that the apparent anticarcinogenic properties of CLA in animal and tissue culture models was not confirmed in this epidemiological study of humans.
