Beef is not recommended for breast cancer

Beef is an abundant dietary source of protein, iron, zinc and B-vitamins. Meat also contains conjugated linoleic acid and stearate, both of which have been shown to induce cancer cell death, including breast cancer apoptosis. However, the potentially favorable effects of these components appear to be overwhelmed by carcinogenic effects of naturally-occurring beef compounds, beef additives and beef preparation methods. Diets high in beef or well-done beef have been linked in multiple population studies to higher risks of leukemia and cancers of the esophagus, lung, stomach, pancreas, kidney, bladder, intestine, colon, rectum, endometrium, testis and prostate. While beef fat may be responsible for some of these results, restricting consumption to lean beef would not eliminate the increased risks of most of these cancers.

Breast cancer-related effects of eating beef

Higher red meat consumption during adolescence by women in the Nurses' Health Study II has been found to be associated with increased risk of premenopausal breast cancer in adulthood. A French population study found that increasing meat consumption was associated with increasing breast cancer risk. A UK study found that both pre- and postmenopausal women who consumed the most meat (including red meat) had the highest risk of breast cancer. A German study of women under 51 years of age also found that breast cancer risk was increased with higher consumption of red meat; women with the highest consumption quartile had an 85% elevated breast cancer risk compared to the lowest quartile. For premenopausal women, the association of meat (especially beef) intake with breast cancer risk was found to be even stronger in this study. A study of tissue removed from healthy women undergoing breast reduction surgery found that the levels of DNA adducts (a type of cancer marker) in the breast tissue was correlated with the women's consumption of fried meat, beef and processed meat. Women in the Iowa Women's Health Study who consistently ate their hamburgers, steak, and bacon very well done were found to have a 4.62 times higher risk of breast cancer than women who consumed the meats rare or medium well done. However, a large 2009 study found no association between meat consumption and breast cancer risk in postmenopausal women.

A number of different factors and mechanisms have been proposed to account for the findings of increased breast cancer risk associated with beef consumption:

The U.S. beef and veal industry uses zeronal (Ralgro), a non-steroidal substance with estrogenic activity, as a growth promoter. Zeronal has been found to stimulate human breast cancer cell growth and proliferation. Other growth promoters (mostly hormones) that are routinely administered to cattle also are suspected to contribute to breast cancer risk.
Irradiation of beef, which is widespread in the U.S., has been found to result in the formation of alkylcyclobutanones, which have been shown to have mutagenic and tumor promoting activities.
Bovine leukemia virus (BLV), which estimated to infect at least 14% of U.S. beef herds, is thought by some observers to be capable of contributing to human breast cancer. Many women have antibodies to BLV, indicating exposure to the virus.
Some of the heterocyclic aromatic amines (HCAs) formed in very well done beef and steak, and in beef gravy, are known human carcinogens. Two of the HCAs, 2-amino-3-methylimidazo[4,5-b]pyridine and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, have also been shown to have potent estrogenic activity, inducing activation of estrogen-regulated genes, proliferation of estrogen-dependent cells and up-regulation of progesterone receptor.
While iron deficiency anemia obviously is to be avoided, the contribution of significant heme iron in the diet as a result of regularly consuming beef could be detrimental for some women. Iron depletion has been shown to lead to significant inhibition of breast cancer cell growth in the laboratory. Relatively high levels of iron in benign breast tissue was found in one prospective study to be associated with an increase in risk of subsequent breast cancer. Other studies have found high levels of iron in the blood to be associated with increased breast cancer risk.

If beef is to be consumed, it makes sense to buy organic beef to avoid irradiated and growth hormone-treated meat.

Additional comments

Well done and flame-broiled beef are not recommended. This includes all fast-food hamburgers. Although they are traditionally used as a base for gravies and sauces, be aware that fat drippings and grill residue scrapings contain particularly high levels of HCAs and ideally should be discarded.

Although we do not recommend supplementation with CLA (conjugated linoleic acid), we wish to advise those who do to avoid the t10,c12-CLA isomer (referred to on some supplement labels as Trans-10, Cis-12). The t10,c12 CLA isomer was found to dramatically enhance mammary tumor development in one mouse experiment. The time by which 50% of the mice in the group developed a tumor was shortened from 267 days for mice on a control diet to 169 days for mice fed t10,c12-CLA. Choose products with only the c9,t11 isomer (Cis-9, Trans-11).

The beef industry appears to take an active interest in academic studies concerning the health benefits and drawbacks of beef. We found several cancer studies that had been financed by the Cattlemen's Beef Board.

Selected studies

Mitogenic activity of zeranol in human breast cancer cells is enhanced by leptin and suppressed by gossypol Anticancer Research, November 2009

The present study was designed to investigate the impact of zeranol, an anabolic growth promoter used by the U.S. beef industry to stimulate cattle growth, on human breast cancer cells. The molecular links between obesity and breast cancer have been studied extensively, but the relationship is not fully clear. Obesity has been shown to significantly increase the risk of breast cancer, as well as increasing the likelihood of death from breast cancer. Leptin (a hormone secreted primarily by fat cells) production is enhanced in obesity. Leptin has also been shown to promote breast cancer cell growth. Zeranol is a growth promoter whereas (-)-gossypol, a polyphenol extracted from cottonseed, has been shown to be chemopreventive. In the study, the effects of leptin, zeranol, and (-)-gossypol on the growth of MCF-7 Adr hormone receptor positive (ER+/PR+) human breast cancer cells were investigated. Leptin was found to enhance the sensitivity of MCF-7 Adr cells to zeranol; the combination increased cancer cell growth. The findings suggest that exposure to zeranol may lead to initiation of transformation of normal breast cells to breast precancerous cells. The authors conclude that obese individuals may be at greater risk of developing zeranol-induced breast cancer as a result of their heightened leptin production.

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 consumption 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.

Meat intake and meat preparation in relation to risk of postmenopausal breast cancer in the NIH-AARP diet and health study International Journal of Cancer, May 2009

The present prospective study was designed to evaluate the association between meat, meat-cooking methods, and meat-mutagen intake and postmenopausal breast cancer in the NIH-AARP Diet and Health Study cohort. A number of studies have found an association between breast cancer risk and intake of red meat or meat cooked at high temperatures, but other studies have found no association. The study included 120,755 postmenopausal women who completed a food questionnaire during 1995-1996 and a detailed meat-cooking survey within six months following baseline. During eight years of follow-up, 3,818 new cases of breast cancer were identified in this study group. After adjusting for covariates, no associations with breast cancer risk were found for consumption of overall total meat, red meat, meat cooked at high temperatures, and meat mutagens. The authors conclude that this major study, which included detailed information on meat preparation methods, provides no support for a role of meat mutagens in the development of postmenopausal breast cancer.

Dietary intake of meat and meat-derived heterocyclic aromatic amines and their correlation with DNA adducts in female breast tissue Mutagenesis, March 2009

The current study was designed to examine the relationship between the intake of meat in general, meat prepared by different cooking methods, and dietary intake of heterocyclic aromatic amines (HCA) with the level of DNA adducts (cancer markers) in the breast tissue of women undergoing breast reduction surgery. Consumption of meat and the associated HCA were determined using a questionnaire in 44 women undergoing reduction mammoplasty. A median DNA adduct level of 18.45 per 109 nucleotides in breast tissue was found to be present; median HCA intake was 40.43 ng/day. The level of DNA adducts in breast tissue was found to be statistically significantly correlated with total HCA intake (r = 0.33, P = 0.03), as well as consumption of fried meat (r = 0.39, P = 0.01), beef (r = 0.32, P = 0.03), and processed meat (r = 0.51, P = 0.0004). However, the detected DNA adducts were not necessarily specific only for HCA, so it is possible that HCA intake reflects intake of other genotoxic substances in meat prepared at high temperatures, such as polycyclic aromatic hydrocarbons.

Meat Intake and Mortality Archives of Internal Medicine, March 2009

The present prospective population study was designed to investigate the relationships between consumption of red, white, and processed meat to risks of total and cause-specific mortality. The study included the National Institutes of Health–AARP Diet and Health Study cohort of half a million people 50 to 71 years old at baseline. Meat consumption was calculated based on a food frequency questionnaire administered at the outset of the study. Cox proportional hazards regression models were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) within quintiles of meat intake. Included in the models were the covariates age, marital status, race, education, family history of cancer (yes/no) (cancer mortality only), body mass index, smoking history, physical activity, calorie intake, alcohol consumption, vitamin supplement use, fruit and vegetable consumption, and hormone replacement therapy among women. The principal outcome measures were total mortality and deaths due to cancer, cardiovascular disease, injury and sudden death, and all other causes. During a follow-up period of 10 years, there were 47,976 deaths among the men and 23,276 deaths among the women. Men in the highest versus lowest quintile of red meat (HR, 1.31 [95% CI, 1.27-1.35]) and processed meat (HR, 1.16 [95% CI, 1.12-1.20]) consumption had elevated risks for overall mortality. Women in the highest versus lowest quintile of red meat (HR, 1.36 [95% CI, 1.30-1.43]) and processed meat (HR, 1.25 [95% CI, 1.20-1.31]) consumption had slightly higher elevated risks for overall mortality. With respect to cause-specific mortality, men and women had elevated risks for cancer mortality for consumption of red meat (HR, 1.22 [95% CI, 1.16-1.29], and HR, 1.20 [95% CI, 1.12-1.30], respectively) and processed meat (HR, 1.12 [95% CI, 1.06-1.19], and HR, 1.11 [95% CI 1.04-1.19], respectively). Cardiovascular disease risk was also elevated for men and women in the highest quintile of red meat (HR, 1.27 [95% CI, 1.20-1.35], and HR, 1.50 [95% CI, 1.37-1.65], respectively) and processed meat (HR, 1.09 [95% CI, 1.03-1.15], and HR, 1.38 [95% CI, 1.26-1.51], respectively) consumption. In comparing the highest and lowest quintiles of white meat consumption, an inverse association was found for total mortality and cancer mortality, as well as for all other deaths for both men and women. The authors conclude that red meat and processed meat intakes were found to be associated with modest increases in total mortality, cancer mortality, and cardiovascular disease mortality.

Red Meat Consumption during Adolescence among Premenopausal Women and Risk of Breast Cancer Cancer Epidemiology, Biomarkers & Prevention, August 2008

The current prospective study was designed to examine the relationship between red meat consumption during adolescence and premenopausal breast cancer. A total of 39,268 premenopausal women within the Nurses' Health Study II who completed validated food questionnaires concerning their diets during high school were followed from 1998 to 2005. There were 455 new cases of invasive premenopausal breast cancer in this group between 1998 and 2005. Compared with women in the lowest quintile of red meat consumption during high school, the multivariate-adjusted RR for the highest quintile was 1.34 (95% CI, 0.94-1.89). The association was found to be statistically significant only for hormone receptor–positive tumors (RR, 1.36; 95% CI, 1.08-1.70). The authors conclude that higher red meat consumption during adolescence may increase the risk of premenopausal breast cancer.

Conjugated linoleic acid induces apoptosis through estrogen receptor alpha in human breast tissue BMC Cancer, July 2008

The current study was designed to examine the roles of conjugated linoleic acid (CLA) in the induction of apoptosis in human breast tissues. CLA is a naturally occurring fatty acid found in milk and beef that has been shown to have anti-cancer actions in animal models and cell culture systems. In human breast cancer, the overall length of estrogen exposure appears to be the most important risk factor for developing estrogen-responsive breast cancer. As such, it has been suggested that estrogen exposure reduces cell death through the up-regulation of the anti-apoptosis protein, Bcl-2. Bcl-2 regulates apoptosis and has a crucial role in the development and growth of both normal and cancerous cells. Extent of Bcl-2 in both normal and cancerous human breast tissues was determined at the beginning of the experiments. Culture of epithelial cells and stromal cells was carried out in the presence or absence of CLA to evaluate apoptosis. Both normal and cancerous breast tissues were positive for Bcl-2 staining, which was found to be high in mammary ducts but very low in the surrounding stromal compartment. In fact, basal Bcl-2 protein levels were found to be higher in normal breast epithelial cells than in cancerous epithelial cells. As expected, treatment with 17beta-estradiol stimulated growth and up-regulated Bcl-2 expression in estrogen-responsive breast epithelial cells. These carcinogenic effects were found to be diminished by both CLA and tamoxifen separately and were reduced further by a combination of CLA and tamoxifen. In both one cell type cultured and co-culture systems, CLA was found to induce cell apoptosis in ERalpha transfected MDA-MB-231 cells but not in the wild type MDA-MB-231 cells, demonstrating that ERalpha plays important roles in CLA-induced apoptosis in human breast tissues.

Epigenetic modulation of protein tyrosine phosphotase methylation by Zeranol in human breast cancer cells American Association for Cancer Research (AACR) Meeting, April 2008

The current study was designed to evaluate the hypothesis that zeranol-induced breast cancer risk is modulated through the methylation of PTP (protein tyrosine phosphatase). Zeranol is a mycotoxin with estrogenic activity that is used in the U.S. beef industry as an anabolic growth promoter. Compounds with estrogenic activity are thought to play a crucial role in breast carcinogenesis since long-term exposure to estrogenic agents has been implicated in heightening breast cancer risk. The authors previously had demonstrated that zeranol induced estrogenic responses in normal human cultured cells, cancerous human breast cells, and breast cancer cell lines, and that therefore, bio-active zeranol metabolites contained in the meat of zeranol-implanted beef cattle should be considered endocrine disruptors for consumers. PTP has been shown act as a potential breast cancer suppressor gene. Data from the authors' laboratory demonstrated that zeranol and estrogen (E2) regulated PTP mRNA expression in normal breast cells and breast cancer cells. They analyzed PTP mRNA expression and methylation patterns in normal and cancerous breast cells by exposing them to 30 nm of zeranol or E2 for 48 hours. High levels of PTP mRNA expression were observed in BT549 breast cancer cells and no promoter PTP methylation was detected. On the other hand, cell lines with low PTP expression (SkBr3, T47D and BT474 cells) showed higher PTP methylation. Zeranol was found to be capable of inducing PTP methylation in MCF-10A normal human breast cells. Beef heifer blood serum collected from heifers implanted with zeranol for 30 days was also found to be more potent in stimulating human breast cancer cell proliferation than the serum of non-implanted heifers. The authors conclude that zeranol-induced PTP methylation may be involved in breast cancer risk by enhancing epigenetic modulation of PTP methylation through consumption of beef from zeranol-implanted cattle.

Dietary factors and breast cancer risk: a case control study among a population in Southern France Nutrition and Cancer, March 2008

The present case-control study was designed to determine the association of various food groups with the risk of breast cancer. 437 cases and 922 controls were matched according to age and geographic location between 2002 and 2004 and were interviewed concerning their diets. Adjusted odds ratios (ORs) were computed for various dietary intakes by two methods: the classical and the spline methods. Neither method found an association between total fruit and vegetable consumption and the risk of breast cancer. Both methods found a nonsignificant reduced risk for increased intake of cooked vegetables, as well as greater legume and fish consumption. Whereas the spline method found no associations, the classical method found the following significant associations related to the lowest consumption of raw vegetables and dairy products: OR = 0.63 for raw vegetable consumption between 67.4 and 101.3 g/day versus lower than 67.4 g/day [95% confidence interval (CI) = 0.43-0.93]; OR = 1.57 (95% CI = 1.06-2.32) for dairy consumption between 134.3 and 271.2 g/day versus lower than 134.3 g/day. However, the overall results were not consistent. Unlike the classical method, the spline method found significant associations for cereal, meat, and olive oil. The spline method found that cereal and olive oil were inversely associated with breast cancer risk and that breast cancer risk increased by 56% for each additional 100 g/day of meat consumed.

Dietary animal-derived iron and fat intake and breast cancer risk in the Shanghai Breast Cancer Study Breast Cancer Research and Treatment, January 2008

The present population-based case–control study was designed to examine the effects of iron and various fats on the risk of breast cancer. While dietary fats have been studied extensively in relation to the risk of breast cancer, iron has received little attention. Iron is an essential micronutrient, however it acts as a pro-oxidant and specific fats may augment its less desirable properties. Participants, including 3,452 breast cancer cases and 3,474 age- and frequency-matched controls, underwent person-to-person interviews, completing a detailed food-frequency questionnaire. Iron and fat intakes were estimated based on dietary data and food composition tables. Unconditional logistic regression models were used to calculate the independent and interactive effects of different forms of iron and fats on the risk of breast cancer. Animal-derived (largely heme) iron intake was found to be positively associated with breast cancer risk (odds ration (OR) = 1.49 in the highest vs. lowest quartile of iron intake, 95% confidence interval [CI] 1.25–1.78; P trend < 0.01) after adjustment for known risk factors, as well as antioxidant vitamin intake, isoflavone intake, and vitamin supplement use. The impact of animal-derived iron was found to be comparable in pre- and postmenopausal women. Intake of animal-derived fats was also associated with increased risk (adjusted OR = 1.34, 95% CI 1.14–1.58), especially after menopause. In addition, a significant interaction between iron and fat from animal sources was observed (P < 0.01). The authors conclude that high intake of animal-derived iron may be associated with an increased risk of primary breast cancer in Chinese women. Furthermore, saturated and mono-unsaturated fats also derived from animal sources may augment this effect.

Meat consumption and risk of breast cancer in the UK Women's Cohort Study British Journal of Cancer, April 2007

The effect of meat consumption on the risk of breast cancer in the UK Women's Cohort Study was evaluated in this study. 35,372 women aged 35 to 69 years between 1995 and 1998 were recruited and their diets were assessed by a 217-item food questionnaire. High intake of meat compared with no meat consumption was found to be associated with premenopausal breast cancer, HR=1.20 (95% CI: 0.86–1.68). Larger effects were found in postmenopausal women for all meat types, with significant correlations with total, processed and red meat consumption. Processed meat had the strongest positive association with postmenopausal breast cancer, with HR=1.64 (95% CI: 1.14–2.37) for high consumption compared with none. The authors conclude that both pre- and postmenopausal women who consumed the most meat had the highest risk of breast cancer.

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.

Red Meat Intake and Risk of Breast Cancer Among Premenopausal Women Archives of Internal Medicine, November 2006

The present prospective study was designed to examine the association between red meat intake and breast cancer by hormone receptor status among premenopausal women. Study participants included 90,659 women ages 26 to 46 years in the Nurses' Health Study II. Red meat intake was determined by a food frequency questionnaire administered in 1991, 1995, and 1999. Respondents were followed up through year-end 2003. Breast cancer cases were self-reported and confirmed by review of pathologic reports. During a follow-up period of 12 years, 1,021 new cases of invasive breast carcinoma were documented. Greater red meat intake was found to be strongly associated with elevated risk of breast cancers that were estrogen and progesterone receptor positive (ER+/PR+; n = 512) but not to cancers that were estrogen and progesterone receptor negative (ER–/PR–; n = 167). Compared to those consuming fewer than four servings of red meat per week, the multivariate relative risks (95% confidence intervals) for ER+/PR+ tumors with increasing servings of red meat intake were (a) 1.42 (1.06-1.90) for five to seven servings per week; (b) 1.20 (0.89-1.63) for seven to 10 1/2 servings per week; and (c) 1.97 (1.35-2.88) for more than 10 1/2 servings per week (test for trend, P = .001). The corresponding relative risks for ER-/PR- breast cancer were 1.21 (0.73-2.00), 0.69 (0.39-1.23), and 0.89 (0.43-1.84) (test for trend, P = .28). The authors conclude that higher red meat intake may be a risk factor for ER+/PR+ breast cancer among premenopausal women.

Nutrition and breast cancer risk by age 50: a population-based case-control study in Germany Nutrition and Cancer, January 2002

The present population-based case-control study was designed to investigate the influence of dietary factors in the risk of breast cancer in a German population of women less than 51 years in age. The study included 706 breast cancer cases and 1,381 controls. In addition to a questionnaire concerning breast cancer risk factors, a subset of 355 cases and 838 controls completed a detailed food questionnaire. The risk of breast cancer was found to be inversely associated with vegetable intake (P for trend = 0.034); the odds ratio (OR) for the highest quartile of vegetable intake compared with the first quartile was 0.64 (95% confidence interval (CI) = 0.43-0.96). Breast cancer risk was found to increase with higher consumption of red meat (P for trend = 0.016); women with the highest consumption quartile had an 85% elevated breast cancer risk compared to the lowest quartile (95% CI = 1.23-2.78). When premenopausal women were considered separately, the protective effect of vegetable intake and the association of meat intake with breast cancer risk were found to be even stronger. The authors conclude that the favorable effect of a diet high in vegetables and low in red meat, especially beef, may be stronger in premenopausal women.

Well-done meat intake and the risk of breast cancer Journal of the National Cancer Institute, November 1998

The current case-control study among members of the Iowa Women's Health Study was designed to assess the potential role of heterocyclic amines and intake of well-done meat on breast cancer risk. Heterocyclic amines formed in meats cooked at high temperatures have been shown to promote mammary cancer in animals. Usual consumption of meat and usual meat preparation practices were determined by a questionnaire which included color photographs showing examples of various levels of doneness of hamburger, steak, and bacon. The study included 273 case subjects and 657 controls. Doneness level of meat and breast cancer risk were found to have a dose-response relationship. The adjusted odds ratios (ORs) for very well-done meat versus rare or medium-done meat were 1.54 (95% confidence interval [CI]=0.96-2.47) for hamburger, 2.21 (CI=1.30-3.77) for beef steak, and 1.64 (CI=0.92-2.93) for bacon. Women who consistently ingested these three meats very well done had a 4.62 times higher risk of breast cancer (CI=1.36-15.70) than women who consumed the meats rare or medium well done. The risk of breast cancer also increased with increasing intake of well-done to very well-done meat. The authors conclude that consumption of well-done meats (and, thereby, exposure to heterocyclic amines or other mutagenic compounds formed as a result of high-temperature cooking) may play a significant role in the risk of breast cancer.

The effect of dietary exposures on recurrence and mortality in early stage breast cancer Breast Cancer Research and Treatment, September 1998

Here, the effects of diet and body weight in 472 women diagnosed with early-stage breast cancer during 1982 to 1984 were studied with respect to eventual breast cancer recurrence and death. The most powerful effects were observed in premenopausal women. It was found that increasing consumption of butter, margarine, and lard (risk ratio (RR)=1.67; 95% confidence interval (CI)=1.17–2.39) and beer (RR=1.58; CI=1.15–2.17) increased the risk of recurrence, after accounting for disease stage and age. An increased risk of recurrence was also found for consumption of red meat, liver, and bacon, corresponding to approximately a doubling of risk for each number of times per day that foods in this category were consumed (RR=1.93; CI=0.89–4.15). Body weight also increased risk at the rate of 9% (RR=1.09; CI=1.02–1.17) for each kg/m2 (equivalent to about 5.8 pounds for a woman 54 inches tall). For risk of death, the results were similar, but relative body weight was more strongly correlated, increasing risk by 12% per kg/m2 (RR=1.12; CI=1.03–1.22).