Validation of a Food Frequency Questionnaire (FFQ) for Assessing Dietary Lignans Intake in Hong Kong Chinese Women with Early-Stage Breast Cancer

Abstract

Background Lignans intake has been suggested to have effects on breast cancer outcomes based on some studies from the West. However, the relationship of lignans consumption and breast cancer outcomes in Chinese population has not been investigated. The development of a culture-specific lignan food frequency questionnaire (LFFQ) is necessary in order to assess dietary lignans intake among Chinese breast cancer patients. This study was designed to validate a newly developed LFFQ to specially assess lignans intake among Chinese subjects. Methods The original study cohort consisted of 1,462 patients with early-stage breast cancer. 133 of these patients were recruited from the original study cohort; 103 of them completed all the assessments from 2015 to 2017 and were included in the present analysis. Two face-to-face interviews were conducted one year apart using a newly developed LFFQ (LFFQ1, LFFQ2). Twelve monthly 24-hour dietary recalls (24-h DRs) were conducted through telephone interview during the same 1-year period. Total lignans intake derived from the LFFQs and 24-h DRs, correlation coefficients and cross classification between the two LFFQs and between LFFQ and 24-h DR were examined. Results Median (IQR) intakes of total lignans for LFFQ1, LFFQ2 and 24-h DRs were 1.66 (1.17–2.15), 1.38 (1.01–2.01), and 0.97 (0.70–1.31) mg/day, respectively. The energy-adjusted validity between LFFQ2 and 24-h DRs was 0.67 (P < 0.001) for log-transformed lignans intake. The reproducibility between lignans intake assessed by the two LFFQs was 0.43 (P < 0.001) for energy-adjusted lignans intake after log transformation. Bland-Altman analysis showed an acceptable agreement between methods (LFFQ and 24-h DR). Correct classification of participants into the same quartiles of energy-adjusted lignans intake after log transformation between LFFQ2 and 24-h DRs and between LFFQs were 42.7% and 37.9%, respectively. Misclassification rates of participants into extreme quartiles were 1.0% and 4.9%, respectively. Conclusion The newly developed LFFQ has acceptable validity and reproducibility, and thus could be regarded as a reasonable and useful instrument in the assessment of dietary lignans intake among Hong Kong Chinese women with early-stage breast cancer.