Consumption of Vegetables and Fruits and Risk of Breast Cancer
Abstract & Commentary
Synopsis: In this prospective, observational study, increased total or specific vegetable and fruit intake did not reduce the risk of breast cancer.
Source: van Gils CH, et al. JAMA. 2005;293:183-193.
The present study was undertaken to test the hypothesis that high fruit and vegetable consumption reduces the risk of breast cancer. A multinational team of investigators conducted a prospective, observational study of the relationship between fruit and vegetable intake and invasive breast cancer as part of the European Prospective Investigation Into Cancer and Nutrition (EPIC) study. Briefly, 285,526 women from several European countries completed a detailed nutritional assessment from 1992 to 1998. The incidence of breast cancer through 2002 was monitored. There were 4148 incident breast cancers, of which 3659 were invasive tumors. The median duration of follow-up was 5.4 years. The median age at diagnosis of breast cancer was 57 years. A variety of statistical models were employed to assess the relationship between fruit and vegetable intake, potential modifiers, and incident breast cancer. Potential modifiers that were modeled included energy intake from fat, saturated fat intake, body size, obesity, body mass index, alcohol intake, smoking, physical activity, age at menarche, exogenous hormone exposure including oral contraceptives, parity, reproductive status, family history, and educational level. More than 90% of the tumors were histologically confirmed. van Gils and colleagues note that this is the largest study of its type to explore this hypothesis.
Comment by Sarah L. Berga, MD
The rationale for the present study was that fruits and vegetables contain several substances thought to protect against the development of cancer, including fiber, antioxidant vitamins and minerals, flavonols, phytoestrogens, and lignans, among others. In the introduction, van Gils et al review the extant data and note that the available data are inconclusive, but suggest that fruits and vegetables may confer a protective effect.
This study is important because diet has been implicated as a causal factor to explain why women in developing countries have a higher incidence of breast cancer. van Gils et al sought to overcome the methodological flaws of earlier studies and it would appear that they have succeeded. The only relationship they found was that the incidence of breast cancer was slightly higher in northern vs southern latitudes.
These findings certainly give pause for thought. There has been a tendency to think that the differential rates of breast cancer between countries might be attributable to certain dietary habits, but van Gils et al were unable to find such an association the consumption of fruits and vegetables. This does not mean that lifestyle factors such as meat intake, alcohol, smoking, exercise, or obesity do not play a role, but it does suggest that the relationships between lifestyle variables and breast cancer are likely to be complex. For the patient and doctor, there are no simple answers here.
Sarah L. Berga, MD, James Robert McCord Professor and Chair, Department of Gynecology and Obstetrics, Emory University School of Medicine is Associate Editor for OB/GYN Clinical Alert.