Dietary Intakes of Flavonols, Flavones and Isoflavones by Japanese Women and the Inverse Correlation between Quercetin Intake and Plasma LDL Cholesterol Concentration

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Abstract
The intake of flavonols, flavones and isoflavones by Japanese women was calculated from our food-phytochemical composition table. The relationship between intake of these phytochemicals and various anthropometric and blood chemistry data was analyzed in a cross-sectional study. The subjects were 115 women volunteers, aged 29–78 y, living in the northern part of Japan. Each subject completed a 3-d dietary record and received a health check up, including urine and blood sampling for biochemical analysis. Total mean intakes of flavonoids (sum of flavonols and flavones) and isoflavones were 16.7 and 47.2 mg/d, respectively. The major source of flavonoids was onions (45.9%) and that of isoflavones was tofu (37.0%). Total intake of isoflavones exceeded that of other dietary antioxidants, such as flavonoids, carotenoids (3.5 mg/d) and vitamin E (8.2 mg/d), and was approximately one half of the vitamin C intake (109 mg/d). The total intake of flavonoids was inversely correlated with the plasma total cholesterol concentration (TC) (r = −0.236, P < 0.05) and plasma LDL cholesterol concentration (LDL-C) (r = −0.220, P < 0.05), after the adjustment for age, body mass index and total energy intake. As a single component, quercetin was inversely correlated with both TC (r = −0.261, P < 0.01) and LDL-C (r = −0.263, P < 0.01). Among Japanese, flavonoid and isoflavone intake is the main component among nonnutrient phytochemicals with antioxidant potential in the diet. These results suggest that a high consumption of both flavonoids and isoflavones by Japanese women may contribute to their low incidence of coronary heart disease compared with women in other countries.