Assessing phytoestrogen exposure in epidemiologic studies: development of a database (United States)

Background and objective: Phytoestrogens (weak estrogens found in plants or derived from plant precursors by human metabolism) have been hypothesized to reduce the risk of a number of cancers. However, epidemiologic studies a ddressing this issue are hampered by the lack of a comprehensive phytoestro gen database for quantifying exposure. The purpose of this research was to develop such a database for use with food-frequency questionnaires in large epidemiologic studies. Methods: The database is based on consumption patterns derived from semistr uctured interviews with 118 African-American, Latina, and white women resid ing in California's San Francisco Bay Area. HPLC-mass spectrometry was used to determine the content of seven specific phytoestrogenic compounds (i.e. the isoflavones: genistein, daidzein, biochanin A, and formononetin; the c oumestan: coumestrol; and the plant lignans: matairesinol and secoisolarici resinol) in each of 112 food items/groups. Results: Traditional soy-based foods were found to contain high levels of g enistein and daidzein, as expected, as well as substantial amounts of coume strol. A wide variety of "hidden" sources of soy (that is, soy protein isol ate, soy concentrate, or soy flour added to foods) was observed. Several ot her foods (such as various types of sprouts and dried fruits, garbanzo bean s, asparagus, garlic, and licorice) were also found to be substantial contr ibutors of one or more of the phytoestrogens analyzed. Conclusions: Databases, such as the one described here, are important in as sessing the relationship between phytoestrogen exposure and cancer risk in epidemiologic studies. Agencies, such as the United States Department of Ag riculture (USDA), that routinely provide data on food composition, on which epidemiologic investigations into dietary health effects are based, should consider instituting programs for the analysis of phytochemicals, includin g the phytoestrogens.