Soya intake and plasma concentrations of daidzein and genistein: validity of dietary assessment among eighty British women (Oxford arm of the European Prospective Investigation into Cancer and Nutrition)

Soya products contain high levels of the isoflavones genistein and daidzein , and their glucosides, and may lower the risk of cardiovascular disease, o steoporosis and cancer. The present cross-sectional study investigated plas ma concentrations of daidzein and genistein and their correlations with die tary soya consumption in four groups of twenty premenopausal British women. The women were selected from the Oxford arm of the European Prospective In vestigation into Cancer and Nutrition using data from food-frequency questi onnaires (FFQ) to guarantee a wide variation in soya consumption, and to in vestigate the utility of the question related to soya milk consumption comp ared with the utility of the question related to other soya foods. Dietary intakes of isoflavones were additionally assessed by 7 d food diaries. Plas ma concentrations of daidzein and genistein were measured by time-resolved fluoroimmunoassay. Geometric mean plasma concentrations (nmol/l) were for t he four groups, which were based on increasing soya intake, 4.9, 8.4, 39.2 and 132 for daidzein and 14.3, 16.5, 119 and 378 for genistein. The Spearma n correlation coefficients for plasma isoflavone concentrations with estima ted dietary intakes were between 0.66 and 0.80 for the diary-based estimate s and between 0.24 and 0.74 for the FFQ-based estimates. The correlations f or soya milk intakes were clearly higher than the correlations for intakes of other soya foods. We conclude that both the food diary and the FFQ estim ate dietary soya isoflavone intakes sufficiently well to use them in epidem iological studies, and that plasma concentrations of daidzein and genistein in Western women who consumed soya products as a part of their regular die t were close to those in Asian populations.