ORIGINAL PAPER Reliability and validity of an assessment of usual phytoestrogen consumption (United States) Pamela L. Horn-Ross Stephen Barnes Valerie S. Lee Christine N. Collins Peggy Reynolds Marion M. Lee Susan L. Stewart Alison J. Canchola Landon Wilson Kenneth Jones Received: 31 March 2005 / Accepted: 5 August 2005 Ó Springer-Verlag 2006 Abstract Objective To evaluate the reliability and validity of a food-frequency questionnaire (FFQ) and database designed to quantify phytoestrogen consumption. Methods This study included 195 members of the Cali- fornia Teachers Study (CTS) cohort who, over a 10-month period, completed four 24-h dietary recalls, a pre- and post- study FFQ, and provided two 24-h urine specimens. Par- ticipants (n = 106) in a parallel study (and 18 women who dropped out of the long-term study) completed a single recall and FFQ, and provided one 24-h urine specimen. Urinary phytoestrogens were determined using liquid chromatography–mass spectrometry. Reliability and validity were evaluated using Shrout–Fleiss intraclass correlations and energy-adjusted deattenuated Pearson correlations, respectively. Results Correlations reflecting the reproducibility of the FFQ phytoestrogen assessment ranged from 0.67 to 0.81. Validity correlations (FFQ compared to dietary recalls) ranged from 0.67 to 0.79 for the major phytoestrogenic compounds (i.e., daidzein, genistein, and secoisolaricires- inol) and 0.43 to 0.54 for the less common compounds. Compared to urinary levels, validity correlations ranged from 0.41 to 0.55 for the isoflavones and 0.16 to 0.21 for total lignans. Conclusion Our isoflavone assessment is reproducible, valid, and an excellent tool for evaluating the relationship with disease risk in non-Asian populations. Further re- search is needed before these tools can accurately be used to assess lignan consumption. Keywords Phytoestrogens Reliability Validity Dietary assessment Urinary excretion Introduction In recent years, substantial interest has developed in the effects of phytoestrogens on the risk of cancer and other chronic diseases. Two classes of phytoestrogens are of primary interest: the isoflavones, found primarily in soy- based foods, and the lignans, found in various whole grains, seeds, legumes, fruits, and vegetables [1, 2]. Most All work was performed at the Northern California Cancer Center with the exception of the laboratory analyses which were performed at the University of Alabama, Birmingham. P. L. Horn-Ross (&) V. S. Lee C. N. Collins A. J. Canchola Northern California Cancer Center, 2201 Walnut Ave., Suite 300, Fremont, CA, 94538, USA e-mail: pam@nccc.org Tel.: +1-510-608-5014 Fax: +1-510-608-5085 S. Barnes L. Wilson K. Jones Departments of Pharmacology and Toxicology and Biochemistry and Molecular Genetics, University of Alabama, Birmingham, AL, USA P. Reynolds California Department of Health Services, Environmental Health Investigations Branch, Oakland, CA, USA M. M. Lee Department of Epidemiology and Biostatistics, School of Medicine, University of California, San Francisco, CA, USA S. L. Stewart Division of General Internal Medicine, Department of Medicine, University of California, San Francisco, CA, USA Cancer Causes and Control (2006) 17:85–93 DOI 10.1007/s10552-005-0391-6 123