Breast Cancer: Red Meat Consumption May Raise Risk

Norra MacReady

June 18, 2014

Women who frequently eat steaks, burgers, and other sources of red meat during their premenopausal years may be raising their risk for breast cancer compared with women who get their protein mostly from poultry, fish, eggs, nuts, and legumes, a new study shows.

In an analysis of nearly 90,000 women, heavy consumption of red meat was associated with a relative risk for breast cancer 22% higher than that seen among women at the lowest end of the meat-eating spectrum, Maryam S. Farvid, PhD, Takemi fellow and associate professor from the Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts, and colleagues report in an article published online June 10 in BMJ.

The authors analyzed data from 88,803 premenopausal women participating in the Nurses Health Study II, a prospective cohort study of female registered nurses who were 24 to 43 years of age in 1989, when the study began. Their average age was 36.4 years (standard deviation, 4.6 years). Nutritional information came from food frequency questionnaires the nurses completed in 1991, 1995, 2003, and 2007. The questionnaires asked about usual intake of 130 foods within the past year. In 1998, the women completed a similar questionnaire exploring their food intake during adolescence. The study participants also provided information about other breast cancer risk factors, including height, weight, race, age at first menarche, parity, age at first pregnancy, menopausal status, use of oral contraceptives, and smoking history.

The authors estimated relative breast cancer risk using Cox proportional hazard models. They also performed multivariate analyses, adjusting for race, family history of breast cancer, history of benign breast disease, smoking history, height, body mass index, age at menarche, parity and age at first birth, use of oral contraceptives, intake of alcohol and calories, and menopausal status. They used the dietary information from the 1991 questionnaire in their primary analysis, "as this represents the dietary intake in early adulthood."

There were 2830 cases of invasive breast cancer during 1,725,419 person-years of follow-up of 88,803 women: 1511 premenopausal cases, 918 postmenopausal cases, and 401 cases in which menopausal status was uncertain. Compared with women in the lowest quintile of red meat intake, the highest level of red meat intake in 1991 was associated with a relative risk (RR) of 1.22 for subsequent breast cancer in premenopausal and postmenopausal women (95% confidence interval [CI], 1.06 - 1.40; P for trend = .01). This positive association persisted after adjusting for total fat intake (RR for highest vs lowest fifth, 1.20; 95% CI, 1.03 - 1.40; P for trend = .04), fruit and vegetable consumption (RR, 1.19; 95% CI, 1.04 - 1.37; P for trend = .03), and intake of heme iron (RR, 1.21; 95% CI, 1.04 - 1.41; P for trend = .03).

"When total red meat intake was modeled as a continuous variable, each additional serving/day increase in total red meat was associated with a 13% increase in risk of breast cancer among all women," the authors write. The relative risk did not change significantly after adjusting for red meat intake during adolescence. "When this relatively small relative risk is applied to breast cancer, which has a high lifetime incidence, the absolute number of excess cases attributable to red meat intake would be substantial, and hence a public health concern," the authors write.

Higher levels of poultry intake were associated with a lower risk for breast cancer (RR for highest versus lowest fifth, 0.73; 95% CI, 0.58 - 0.91; P for trend = .02). Each additional daily serving lowered the risk for postmenopausal breast cancer by 25% (RR, 0.75; 95% CI, 0.58 - 0.98). There was no association with premenopausal cancer risk. Replacing 1 daily red meat serving with a serving of poultry lowered breast cancer risk by 17% (RR, 0.83; 95% CI, 0.72 - 0.96). Substituting 1 serving of legumes per day for a serving of meat lowered the risk among all women by 15% (RR, 0.85; 95% CI, 0.73 - 0.98). In addition, risk was lowered by 14% when fish, nuts, legumes, and poultry were combined to substitute for 1 serving/day of meat (RR, 0.86; 95% CI, 0.78 - 0.94).

These findings are not consistent with other studies, in which there was no association between red meat intake and breast cancer risk, the authors write. "However, most of the results have been derived from diet during midlife and later, and red meat intake during early adulthood may be more related to an increased risk of breast cancer. Carcinogenic byproducts such as heterocyclic amines and polycyclic aromatic hydrocarbons, created during high temperature cooking of meat; animal fat and heme iron from red meat; and hormone residues of the exogenous hormones for growth stimulation in beef cattle are some of the mechanisms that may explain the positive association between high intake of red meat and risk of breast cancer."

Study limitations include use of a predominantly white, well-educated, middle-class cohort; reliance on food frequency questionnaires, which usually include some measurement errors; and inability to control for unknown residual confounders. Strengths include the large number of cases and the prospective design.

"This analysis supports an association between higher consumption of total red meat during early adulthood and increased risk of breast cancer that was not clearly restricted to breast cancers in premenopausal women," the authors conclude. "Consistent with the American Cancer Society guidelines, replacement of unprocessed and processed red meat with legumes and poultry during early adulthood may help to decrease the risk of breast cancer."

This study was supported by a grant from the National Institutes of Health. The authors have disclosed no relevant financial relationships.

BMJ. 2014;348:g3437. Full text

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