Data regarding convenient, valid methods for measuring U.S. isoflavone intake are limited. We evaluated a soy food questionnaire (SFQ), the Willett food frequency questionnaire (FFQ), and overnight urine samples relative to excretion in 24-h urine samples. We also described intake among women in a high-risk program for breast or ovarian cancer. Between April 2002 and June 2003, 451 women aged 30 to 50 yr with a family history of breast or ovarian cancer completed the SFQ and FFQ. Of them, 27 provided four 24-h and overnight urine specimens. In these women, 24-h sample measures were correlated with SFQ estimates of daidzein (Spearman r =.48) and genistein (r =.54) intake, moderately correlated with the Willett FFQ (daidzein r =.38, genistein r =.33), and strongly correlated with overnight urine excretion (daidzein r =.84, genistein r = 0.93). Among all 451 SFQ respondents, mean (median) daidzein and genistein intakes were 2.8 (0.24) and 3.9 (0.30) mg/day. Primary sources of both were soymilk, soy nuts, and tofu. We conclude that targeted soy food questionnaires, comprehensive FFQs, and multiple overnight urines are all reasonable options for assessing isoflavone intake in epidemiologic studies.
Bibliographical noteFunding Information:
This work was supported by grants from the Cancer Research and Prevention Foundation, Grant CA–096414 from the National Institutes of Health, and grant IRG–92–027–09 from the American Cancer Society. We thank Etyia Faison for her extensive work in data collection, Andrew Balshem and his facility for data entry and management, and Cynthia Spittle and Rita Michielli for their assistance in processing specimens for analysis.