Early Life and Adult Exposure to Isoflavones and Breast Cancer Risk

Abstract

Soy and red-clover isoflavones are commonly consumed within the diet or as a dietary supplement due to a range of presumed beneficial health benefits. These isoflavones are thought to protect against heart diseases as well as breast and other types of cancer. Isoflavones are structurally similar to estrogens and may act as estrogen agonists or antagonists by binding to estrogen receptors. Because of an increased use of isoflavones in processed foods and dietary supplements as well as the greater consumption of soy products, dietary intakes of isoflavones are increasing in children and adolescents in North America. Estrogens are a known component of numerous hormone related cancers including breast cancer. It is with these facts in mind that we review the existing epidemiological and experimental animal studies for a resolution to a proposed correlation between increased isoflavone consumption and breast cancer. There is conflicting evidence from epidemiological, intervention and experimental animal studies regarding the chemopreventing effects of soy isoflavones in breast cancer. Isoflavones are weak estrogens and their effect depends upon the dose, time of exposure and species involved. It would, therefore, not be safe to indisputably accept soy or red-clover as a source of isoflavone resource to prevent breast cancer.

Key Words:

• breast cancer
• early life exposure
• isoflavone
• phytoestrogen
• risk assessment

Acknowledgments

Renee Shiao worked as a summer intern during 2005 for the Office of Environmental Health Hazard Assessment. The views expressed are those of the authors and do not necessarily represent those of the Office of Environmental Health Hazard Assessment, the California Environmental Protection Agency or the State of California.

The authors thank Dr. C.S. Hsieh for her critical reading and suggestions and Ms. Ruchika Tomar for her editorial assistance.

Notes

¹USDA-Iowa state university isoflavone data base (2002) (105).

¹OR/RR (CI), Odd ratio/relative risk (95% confidence interval).

²Breast cancer cases/ and Controls in the study.

³All women participating in the study.

⁴Women stratified into premenopausal status.

⁵Women stratified into postmenopausal status.

⁶Not statistically significantly different in the trend test.

¹OR/RR (CI), Odd ratio/relative risk (95% confidence interval).

¹OR/RR (CI), Odd ratio/relative risk (95% confidence interval).