Background: Red meat consumption has been associated with an increased risk of breast cancer. Although a case-control trial found this association, prospective cohort studies cannot consistently connect red meat intake with a risk of breast cancer. However, these studies did not have many participants who were young and premenopausal.

The number of women 40 to 49 years of age with hormone-receptor–positive breast cancer has increased. Some components of red meat are estrogenic and may affect breast cancer through hormone receptors, indicating that dietary habits in early adulthood may have an effect on this risk. Cho and colleagues evaluated the effect of red meat consumption on the risk of breast cancer in premenopausal women.

The Study: Participants included nurses involved in the Nurses Health Study II who were premenopausal and had completed most of a dietary questionnaire. Women were excluded if they had natural or surgical menopause during the study or if they had a hysterectomy and menstrual status could not be verified. More than 130 questions about dietary intake were included in the questionnaires for 1991, 1995, and 1999. Red meat was defined as beef, lamb, and pork, as well as hamburger, bacon, hot dogs, and other processed meats. The cumulative average consumption of red meat was calculated using the responses from the questionnaire, and women with breast cancer were identified by a specific question during follow-up mailings until 2003. In the event of death, an attempt was made to identify the cause. If the participant was diagnosed with breast cancer, the authors reviewed pathology reports to confirm the diagnosis and recorded the hormone-receptor status.

Results: Of the 90,659 participants, 1,021 were diagnosed with invasive premenopausal breast carcinoma. Although a high intake of red meat was weakly associated with an over-all increased risk of breast cancer, there was a strong association between the intake of red meat and the risk of hormone-receptor– positive breast cancer. Consuming red meat was not associated with an increased risk of hormone-receptor–negative breast cancer. Compared with participants who ate three or fewer servings of red meat per week, women who had four to five servings per week had a relative risk of breast cancer of 1.14. Those who consumed more than 1.5 servings per day had a relative risk of 1.97.

Conclusion: Red meat intake was associated with a higher risk of hormone-receptor– positive breast cancer in premenopausal women. Moreover, a higher consumption of red meat during the study increased the risk of invasive hormone-receptor–positive breast cancer. Because few breast cancer risk factors are modifiable, the authors add that these findings have potential health implications in preventing breast cancer.