The Mediterranean Diet is a well-known healthy regimen that can reduce the risk of cardiovascular disease. Now, a new study has found that it may reduce the risk of breast cancer. The findings were published online on September 15 in the journal JAMA Internal Medicine by researchers in Spain and their colleagues at Harvard Medical School.
The study authors note that breast cancer is the most frequently diagnosed malignant tumor and the leading cause of cancer death among women; in addition, its incidence is increasing. In 2012, 1.7 million women were diagnosed with the malignancy. Since the 2008 estimates, breast cancer incidence has increased by more than 20% worldwide, and mortality has increased by 14%.1 In European nations, breast cancer is the most common cancer and the first or second (after lung cancer) malignancy implicated in mortality among women.
The authors explain that diet has been extensively studied as a modifiable component of lifestyle, which could influence breast cancer development. However, epidemiological evidence on the effect of specific dietary factors remains inconsistent, and the only convincing evidence relates to an increased risk in women with high alcohol consumption.
To gain understanding of the effect of diet on breast cancer risk, the researchers evaluated the effect of two interventions with Mediterranean diet compared to the advice to follow a low-fat diet (control group) on breast cancer incidence. They reviewed data from the PREDIMED study, which was a randomized trial conducted at primary healthcare centers in Spain. From 2003 to 2009, 4,282 women aged 60 to 80 years and at high cardiovascular disease risk were asked to enroll in the study by their primary care physicians.
The women were randomly assigned to a Mediterranean diet supplemented with extra-virgin olive oil, a Mediterranean diet supplemented with mixed nuts, or a control diet (advice to reduce dietary fat). The main outcome measurement was breast cancer incidence among women without a past history of breast cancer (4,152 women).
After an average follow-up of 4.8 years, the researchers identified 35 confirmed incident cases of breast cancer. Observed rates (per 1,000 person-years) were 1.1 for the Mediterranean diet with extra-virgin olive oil group, 1.8 for the Mediterranean diet with nuts group, and 2.9 for the control group. The breast cancer risk compared to the control group was a 68% risk reduction for the Mediterranean diet with extra-virgin olive oil group and 41% risk reduction for the Mediterranean diet with nuts group. In analyses that incorporated yearly cumulative updated dietary exposures, the risk reduction for each additional 5% of calories from extra-virgin olive oil was 28%.
The authors note that their study was the first randomized trial finding an effect of a long-term dietary intervention on breast cancer incidence. They concluded that their results suggested a beneficial effect of a Mediterranean diet supplemented with extra-virgin olive oil in the primary prevention of breast cancer. They recommended that further large, long-term studies should be conducted to confirm their findings.
