Dietary Intake and Plasma Levels of Isoflavones Among Breast Cancer Survivors

Abstract

Abstract Objectives Isoflavones, rich in soybeans, are phytoestrogens with a similar chemical structure to estrogen and their roles in breast cancer prognosis remains equivocal. We aimed to estimate dietary intake of isoflavones and soy and examine their correlations with plasma levels of isoflavones among Korean breast cancer survivors. Methods A total of 974 female breast cancer survivors (mean age, 52 years) were included in the cross-sectional study. We estimated dietary intake of soy and isoflavones using either a 3-day food record (3DR; n = 645) or a food frequency questionnaire (FFQ; n = 329). Plasma isoflavone levels were measured by liquid chromatography methods in 439 participants. We calculated total isoflavones by summing daidzein, genistein, and glycitein. We estimated % contribution of food sources to dietary isoflavone intake and Pearson correlation coefficients with plasma isoflavone levels. We calculated de-attenuated correlations among those who reported dietary intake using 3DRs to reduce within-person variation (n = 233). Results The mean daily intake of total isoflavones among Korean breast cancer survivors was 21.91 mg/d. The major sources were tofu (% contribution = 30.6%), soybean (14.2%), and soybean sprouts (12.8%). The correlation coefficients with plasma isoflavone levels were 0.19 for dietary isoflavone intake and 0.18 for soy and its products intake. The de-attenuated correlation coefficients with plasma isoflavone levels were 0.25 for dietary isoflavone intake and 0.35 for soy and its products intake. When we examined the correlation between specific type of isoflavone and circulating level of each isoflavone, the de-attenuated correlation coefficients were 0.18 for daidzein, 0.28 for genistein, and 0.25 for glycitein. Conclusions We found the highest contribution from tofu and soybean to dietary isoflavone intake and moderate correlations of dietary intakes of soy and isoflavones with plasma levels of isoflavones among Korean breast cancer survivors. Our study warrants further investigation on the roles of isoflavones in breast cancer prognosis. Funding Sources This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (Ministry of Science and ICT, MSIT) (No. 2019R1F1A1061017).