Reliability and validity of an assessment of usual phytoestrogen consumption (United States).
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.


CONCLUSIONS
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.
Horn-Ross
Pamela L
PL
Northern California Cancer Center, 2201 Walnut Ave., Suite 300, Fremont, CA 94538, USA. pam@nccc.org
Barnes
Stephen
S
Lee
Valerie S
VS
Collins
Christine N
CN
Reynolds
Peggy
P
Lee
Marion M
MM
Stewart
Susan L
SL
Canchola
Alison J
AJ
Wilson
Landon
L
Jones
Kenneth
K
D000328:Adult; D000368:Aged; D002140:California; D016009:Chi-Square Distribution; D002853:Chromatography, Liquid; D015930:Diet Records; D005260:Female; D006801:Humans; D013058:Mass Spectrometry; D008875:Middle Aged; D048789:Phytoestrogens / Q000008:administration & dosage* / Q000652:urine; D011446:Prospective Studies; D015203:Reproducibility of Results
D048789:Phytoestrogens