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Abstract
Some forms of estrogen are associated with breast cancer risk as well as with mammographic density (MD), a strong marker of breast cancer risk. Whether phytoestrogen intake affects breast density, however, remains unclear. We evaluated the association between serum levels of phytoestrogens and MD in postmenopausal women. We enrolled 269 women, ages 55–70 yr, who received a screening mammogram and had no history of postmenopausal hormone use. Subjects completed a survey on diet and factors related to MD and provided a blood sample for analysis of 3 phytoestrogens: genistein, daidzein, and coumestrol. We examined whether mean percent MD was related to serum level of phytoestrogens, adjusting for age and body mass index. Genistein and daidzein levels correlated with self-reported soy consumption. Mean percent MD did not differ across women with different phytoestrogen levels. For example, women with nondetectable genistein levels had mean density of 11.0% [95% confidence intervals (CI) = 9.9–12.4], compared to 10.5% (95% CI = 8.0–13.7) and 11.2% (95% CI = 8.7–14.6) for < and ≥median detectable levels, respectively. In a population with relatively low soy intake, serum phytoestrogens were not associated with mammographic density. Additional studies are needed to determine effects of higher levels, particularly given patterns of increasing phytoestrogen intake.
ACKNOWLEDGMENTS
This work was supported by the Komen for the Cure Foundation (FAS0703857), the Department of Defense (BC062649), and the National Cancer Institute (CA139548, CA014520). Brian Sprague is supported by a fellowship from the American Society of Preventive Oncology, Susan G. Komen for the Cure, and the Prevent Cancer Foundation. The authors would also like to express gratitude to the participants for their contributions to the project, to the staff of the University of Wisconsin (UW) Health Clinics and the UW Office of Clinical Trials for their assistance in subject recruitment and data collection, to Noel Weiss for providing feedback on an earlier draft of the manuscript, and to Chris Peressotti, Martin Yaffe, Karen Cruickshanks, and Julie McGregor for study advice and support.