Reliability and Validity of an Assessment of Usual Phytoestrogen Consumption (United States)
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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 California 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. Participants (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 secoisolariciresinol) 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 research is needed before these tools can accurately be used to assess lignan consumption.
KeywordsPhytoestrogens Reliability Validity Dietary assessment Urinary excretion
The authors would like to thank the CTS Steering Committee who are responsible for the resource within which this substudy was conducted: Hoda Anton-Culver, Leslie Bernstein, Dennis Deapen, Harvey Mohrenweiser, David Peel, Rich Pinder, David M. Purdie, Ronald K. Ross, Daniel O. Stram, Dee W. West, William E. Wright, and Argyrious Ziogas; the following people who provided technical or administrative support: Mia Cruz, Kristi Jogis, Lorraine Lindow, Diana Lee, Kristina Rickmond, Amy Shiau, Erin Silva, Jan Stewart, and Orawan Takaki; and all the participants who donated their time to this intensive study. This research was supported by grant R01 CA77398 and cooperative agreement U01 CA81789 from the National Cancer Institute and contract 97-10500 from the California Cancer Research Fund. The mass spectrometer used in this study was provided by funds from a NCRR Shared Instrumentation Award (S10 RR06487) and institutional funds from the University of Alabama at Birmingham. Operational support for the Mass Spectrometry Shared Facility came from a National Cancer Institute Core Support grant to the UAB Comprehensive Cancer Center (P30 CA-13148).
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