a Total flavonoid are often given as a sum of the subgroups listed excl. the catechins and anthocyanins. b Data from Justesen et al. (2000).
c Dragsted et al. (1997) based on Danish consumption levels. d Sampson et al. (2002). e Hertog et al. (1993c). f Arts et al. (2001c). g Kumpulainen et al (1999). h Average daily intake in Finland, Heinonen (2001). i Data obtained from Arai et al (2000). n.d. = no data available.
The flavanonols, also called dihydroflavonols, are found only in trace amounts in plants, and are therefore not important constituents in the human diet (Pierpoint, 1986). The contribution offlavones to the human intake of flavonoids is generally limited; however, some spices and herbs contain high amounts of flavones. Parsley, for instance, contains large amounts of apigenin (Justesen et al., 1998), and the highly methylated flavone tangeretin is found in the peel of citrus fruits, and can thus occur in juices made from whole fruits (Pierpoint, 1986).
The flavonols are one of the major groups of flavonoids present in the human diet. Quercetin is the most abundant flavonol, found ubiquitously in fruits and vegetables and is especially present in high amounts in onions, cruciferous, apples, wine and tea. Kaempferol, found in broccoli, kale and tea, and myricetin, found in tea and wine, are also major flavonols found in the human diet (Hertog et al., 1992, 1993b).
The isoflavones are present only in legumes, especially in soybean. The European intake of isoflavones is therefore limited, but in Asia and especially in Japan, where soy are consumed in large amounts, the intake is considerable, and as seen in Table 9.1 it exceeds the intake of all other flavonoids.
Catechins are quantitatively a quite large group within the human diet. They either occur as free catechins or are derivatised with gallic acid, and are found mainly in green and black tea, chocolate and wine (Forsyth, 1955; Rimm et al., 1996a). In countries with a high intake of tea, such as Japan (mainly green tea) and the United Kingdom (black tea), the daily intake of catechins is substantial. As seen in Table 9.1, the average intake of the strongly coloured anthocyanins may also be extensive, in particular for regular consumers of red wine, blackcurrant juice, berries, and red grapes.
The estimated average daily intake of flavonoids including catechins and anthocyanins is thus well above 50 mg for all countries presented in Table 9.1 and the real intake is probably higher than 100 mg/day if data on all flavonoid subgroups were available. The daily intake of other dietary antioxidants such as vitamin C (80mg/day), vitamin E (8.5 mg/day) and ^-carotene (1.9 mg/day) (Nielsen, 1999a) is comparable to or considerably lower than the intake of the flavonoids, so these compounds certainly constitute an important part of the daily intake of dietary antioxidants.
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