ABSTRACT & COMMENTARY
Red Meat and Increased Breast Cancer Risk
By Traci Pantuso ND, MS
Adjunct Faculty, Bastyr University, Seattle, WA
Dr. Pantuso reports no financial relationships relevant to this field of study.
- According to this study, each daily serving of red meat increased relative risk of breast cancer by 13%.
- Higher poultry intake is associated with a lower incidence of breast cancer in postmenopausal women.
- Replacing one serving per day of red meat with a combination of poultry, legumes, fish, eggs, and nuts reduces the relative risk of breast cancer.
In this study, the authors investigated the relationship between dietary protein sources during early adulthood in women and overall breast cancer risk. Previously, Cho and colleagues reported that increased red meat intake was associated with greater risk of breast cancer in premenopausal women who participated in the Nurses’ Health Study II (NHII) cohort. The current study found that red and processed meat intake in early adulthood may increase the risk of breast cancer in women, but eating legumes, nuts, poultry, and fish reduced the risk of breast cancer in the NHII cohort.
Farvid MS, et al. Dietary protein sources in early adulthood and breast cancer incidence: Prospective cohort study. BMJ 2014;348:g3437.
The majority of the research has demonstrated no significant association between breast cancer and red meat intake, but most of these studies examined meat intake at midlife, not in early adulthood when environmental cancer pathophysiology may occur.1 Red and processed meat intakes have been associated with an increasing risk of colorectal, esophageal, liver, and prostate cancers, but not breast cancer.
METHODS
The study population was the Nurses’ Health Study II, a prospective cohort study that started in 1989; participants included 116,430 female nurses who were aged 24-43 years old in 1989. A food frequency questionnaire (FFQ) was given in 1991 regarding their dietary intake in the past year. A total of 97,813 women answered the questionnaire; 9010 women were excluded from the study, meaning that data came from a total of 88,803 women. Exclusion criteria included the following:
- Diagnosis of diabetes, coronary heart disease, or stroke
- Diagnosis of any cancer other than non-melanoma skin cancer
- Missing data on red meat intake or age
- Being postmenopausal
- 70 or more of the FFQ items were left unanswered
- Dietary intake that was < 2508 kJ (599 kcal) or ≤ 14,630 kJ (3496 kcal)
Diet Evaluation
In 1991, 1995, 1999, 2003, and 2007, participants completed a semi-quantitative FFQ that evaluated usual dietary intake and alcohol use in the past year. Items related to red meat that were evaluated consuming either unprocessed red meat (beef, pork, or lamb as a sandwich, pork as a main dish, beef or lamb as a main dish, and hamburger) or processed red meat (hot dogs, bacon, and other processed meat such as sausage). Other protein sources such as eggs, poultry, legumes, and nuts were also measured.
Food intake measured in 1998 included an assessment of foods that were consumed during 1960-1980 when these women would have been in high school. Nutrient intakes were calculated by multiplying the frequency of consumption of each item by the nutrient content of the reported portion sizes and then adding up the items. Nutrient values were taken from the USDA, food manufacturers, independent academic sources, and investigators’ own fatty acid analysis for commonly used products.
Breast Cancer Measurement
Breast cancer cases were evaluated based on the biennial questionnaires with hospital and pathology reports when available. Eighty-eight percent of medical records were obtained and 98% of self-reported breast cancer cases were confirmed through review of pathology reports. Cases of carcinoma in situ were excluded from the analysis. Estrogen and progesterone receptor status was determined by the pathology reports.
Additional variables measured included:
- Age, height, weight, smoking status
- Family history of breast cancer, history of benign breast disease
- Age at menarche, oral contraceptive use
- Parity, age at first birth
- Menopausal status, postmenopausal hormone use, and age at menopause.
According to food group or nutrient intake, women were divided into five categories from highest to lowest dietary intakes. Cox proportional hazards models were used to calculate relative risk and 95% confidence intervals (CI). To assess interactions with additional variables, multivariate analysis was performed.
RESULTS
Between 1991 and 2011, a total of 1,725,419 person years data from 88,803 premenopausal women was obtained, and 2830 invasive breast cancer cases were identified, including:
- 1511 premenopausal breast cancers
- 918 postmenopausal breast cancers
- 401 cancers in women of uncertain menopausal status.
The average age of the participants in 1991 was 36.4 years, with a range of 26-45 years. The average age of diagnosis in premenopausal women was 45, with a range of 27-60 years. In postmenopausal women, the average age was 55 with a range of 39-64 years.
Women in the highest red meat quintile had a median intake of 1.5 serving/day compared to women in the lowest quintile who had a median intake of 0.14 serving/day.
Women in the highest red meat quintile demonstrated a 22% increased relative risk (RR) of breast cancer compared to women with the lowest intake (RR, 1.22; 95% CI, 1.06-1.40; Ptrend = 0.01 for highest quintile vs lowest). After controlling for total fat intake, the relative risk was still significant (RR, 1.20; 95% CI, 1.03-1.40; Ptrend = 0.04). Women who had a median intake of 1.5 serving/day of red meat compared to those that had 0.14 serving/day had a 22% increased relative risk of breast cancer with each additional daily serving of red meat increasing the relative risk of breast cancer by 13% (RR, 1.13; 95% CI, 1.04-1.22; see Table 1).
Red meat intake during adolescence did not appreciably change the relative risk of breast cancer overall (RR, 1.20; 95% CI, 1.07-1.34) or the risk of premenopausal breast cancer (RR, 1.24; 95% CI, 1.07-1.44). With additional adjustment for menopausal status, oral contraceptive use, body mass index, smoking, height, age at menarche, age at menopause, parity and age at first birth; red meat intake during adolescence changed little for breast cancer overall (RR, 1.18; 95% CI, 1.06-1.33) and for premenopausal breast cancer (RR, 1.20; 95% CI, 1.03-1.40).
The study also found that women who consumed more red meat had higher energy intake, were heavier, were more likely to smoke, and were more likely to have three or more children. These women were also less likely to use oral contraceptives and to have a history of benign breast disease. The authors controlled for these findings through their multivariate statistical model with additional adjustments for these potential confounders.
Eating poultry was associated with a lower risk of postmenopausal breast cancer (RR, 0.73; 0.58-0.91; Ptrend = 0.02) and the estimate was unchanged when adjusted for fruits, fat, or vegetable intake. The cumulative average intake of poultry by premenopausal women was associated with a lower relative risk of postmenopausal breast cancer. There was a 25% lower risk of postmenopausal breast cancer per serving of poultry/day (RR, 0.75; 95% CI, 0.58-0.98).
Legume, fish, egg, and nut intakes were not associated with either post- or premenopausal breast cancer risk. Replacing one serving per day of red meat with a combined serving of legumes, nuts, poultry, and fish reduced the relative risk of breast cancer in women overall.
COMMENTARY
Breast cancer is the second leading cause of cancer in the U.S. population and the number one cause of cancer in women. During 2014, 232,670 new cases are expected and 40,000 deaths are expected to be due to breast cancer in the United States.2 In addition, 12.3% of women in the United States are expected to receive a diagnosis of breast cancer during their lifetime.2 This study found that a median intake of 1.5 servings of red meat per day had a 22% increased relative risk of breast cancer compared to women with the lower intake of 0.14 serving/day. Each additional serving of red meat increased the relative risk of breast cancer another 13% in women. Because of the high incidence of breast cancer, dietary intake of red and processed meats may be a significant risk factor and is also a modifiable factor.
The strengths of this study are the number of participants, the large number of breast cancer cases and the long follow-up period. There are a number of limitations to this study. The study population was predominately white educated women from the United States, making the conclusions less generalizable to other populations. Another limitation with this study is that genetic predispositions such as breast cancer gene (BRCA) mutations were not measured and have been shown to increase overall breast cancer risk in women. Exercise was also not measured in this study, a clear and proven variable in breast cancer risk. Another limitation of this study is that risks related to unprocessed meat servings were calculated together rather than evaluated individually, and the chemicals in processed meat may have been an important contributing factor to breast cancer development. Nitrites and nitrates are used to preserve processed meats and can undergo a process of nitrosation, which occurs spontaneously with these compounds. The resulting compounds have been declared to be “probable human carcinogens” by the International Agency for Cancer Research in 1996.3
Despite the limitations of this study, the increased relative risk of breast cancer with red meat intake in women is notable and also modifiable. Although there is not a larger body of evidence suggesting that increased red meat intake increases relative risk of breast cancer, there is evidence for increased risk of colorectal, esophageal, liver, and prostate cancer.3 All of these are compelling reasons to pay attention to this aspect of someone’s diet. It is also recommended to encourage patients to eat red meat products that are procured from grass-fed animals without additional hormones and to avoid processed meats that contain chemicals such as nitrites.
Conclusion
Recommending a diet such as the Mediterranean diet pattern that is low in red meat emphasizing vegetables, fruit, legumes, and healthy fats with poultry is a reasonable recommendation to reduce the risk of cancer and promote overall health.4,5
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Table 1. Percent Increased Breast Cancer Relative Risk by Group
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% Increased Risk per Additional Serving of Red/Processed Meat
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RR
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95% CI
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All women
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13
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1.13
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1.04-1.22
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Premenopausal women
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12
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1.12
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1.01-1.25
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Postmenopausal women
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8
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1.08
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0.94-1.23
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REFERENCES
- Cho E, et al. Red meat intake and risk of breast cancer among premenopausal women. Arch Intern Med 2006;166:2253-2259.
- Abid Z, et al. Meat, dairy and cancer. J Nutr 2014;100(Suppl 1):386S-393S.
- National Cancer Institute. Surveillance, Epidemiology and End Results Program. SEER Stat Fact Sheets: Breast Cancer. Available at: http://seer.cancer.gov/statfacts/html/breast.html. Accessed Sept. 4, 2014.
- Bonaccio M, et al. The Mediterranean diet: The reasons for a success. Thromb Res 2012;129:401-404.
- Samieri C, et al. The association between dietary patterns at midlife and health in aging. Ann Intern Med 2013;159:584-591.
