Dietary intake of flavonoids

The same authors [204] confirmed these results in the Seven Country Study. The contribution of flavonols and flavones in explaining the variance in coronary heart disease mortality rates across 16 cohorts from seven countries was studied. Flavonol and flavone intake was inversely correlated with mortality from coronary heart disease. These finding are in line with the results of a cohort study in Finnland [205], where a significant inverse gradient was observed between dietary intake of flavonoids and total and coronary mortality. 

Not all the effects of dietary intake of flavonoids are positive. The excessive consumption of soybean and its products has been considered goitrogenic in humans and animals. Several researchers have reported induction of goitre in iodine-deficient rats maintained on a soybean diet [125, 126, 127], In some cases, the extreme intake of soybean has been correlated with cancer. Thus, Kimura et al reported the induction of thyroid carcinoma in rats fed on defatted soybean deficient in iodine by up to 40% [128],... 

In the Zutphen Elderly Study (in Holland) carried out on 805 men aged 65-84 years, dietary intake of flavonoids was calculated during a five-year period. The study indicates that the intake of flavonoids is inversely associated with mortality from coronary heart disease and, to a lesser extent, myocardial infarct. The main source of flavonoids in the men s diets were tea, onions and apples. These flavonoids include quercetin, kaempferol and myricitin as well as the catechin-type condensed tannins found in black tea (Hertog et al. 1993). 

Weame S. Estimating dietary intakes of flavonoids. In Rice-Evans C, ed. Wake Up to Flavonoids. London Royal Society of Medicine Press, 2000 35-43. 

Flavonoids are part of the hiunan diet, and high levels occm in fruits, vegetables, wine, tea, and cocoa. It is suggested that dietary intake of flavonoids has beneficial health effects due to their antioxidant and radical-scavenging properties... 

Table 2 Estimated dietary intake of flavonoid subclasses in different countries...

The flavonoid database described in this chapter was applied to 4-day weighed food records obtained from healthy Scottish men n = 41) and women ( = 52) to provide a provisional estimate of flavonoid intake in Scotland. All subjects consumed foods containing flavonols, procyanidins, and catechins, dietary intakes of which are given in Table 4.15. The main flavonol consumed was quercetin, accounting for 66 and 63% of the total flavonol intake of 18.8 mg/day. Primary sources of flavonols were from black tea (42.7%), onions (14.3%), apples (10.2%i), and lager (7.2%i) (Table 4.16). 

A comprehensive and critical review of food flavonoid literature has led to the development of a food composition database for flavonols, flavones, procyanidins, catechins, and flava-nones. This database can now be used and continuously updated to estimate flavonoid intake of populations, to identify dietary sources of flavonoids, and to assess associations between flavonoid intake and disease. However, there is a need for better food composition data for flavones, procyanidins, and flavanones as current literature is sparse particularly for citrus fruits, fruit juices, and herbs. In addition, anthocyanin food composition data are lacking although validated methods of determination are becoming available. 

In the Finnish Mobile Clinic examination there was an inverse relation between the dietary intake of some flavonoids and the incidence of several chronic diseases, The positive outcome was related to the consumption of apples, The authors concluded, although our finding was independent of the intake of antioxidant vitamins, the potential... 

In contrast to epidemiological studies of these diseases, there has been just one study that compared flavonoid intake and cataract [44]. In this Finnish study the dietary intakes of over 10,000 men and women were estimated for the year preceding baseline health examination. Health outcomes were determined 28-30 years later using Finnish government health statistics and compared with the highest and lowest intakes. Neither higher total flavonoid intake nor higher intakes of quercetin, kaempferol, myricetin,... 

In contrast to many studies that identify beneficial effects of dietary flavonoids against cellular Hpid oxidation, the action of flavonoids on bovine leukemia virus-transformed lamb fibroblasts (line FLK) and HL-60 cells was accompanied by lipid peroxidation [90]. Their toxicity was partly prevented by iron chelator desferrioxamine and antioxidant AA iphenyl-p-phenylene diamine, a result that pointed to the involvement of oxidative stress in their cytotoxicity. Interestingly, the toxicity of quercetin was partly prevented by nontoxic concentrations of other flavonoids examined, thus suggesting potential neutralization of quercetin cytotoxicity by intake of flavonoid mixtures. In another study, supplementation of rat hepatocyte cultures with the flavonoid myricetin led to the formation of phenoxyl radical intermediates, as detected in intact cells by electron paramagnetic resonance (EPR) spectroscopy [220]. These phenoxyl radicals corresponded to one-electron oxidation products of... 

Estimation of the daily intake of flavonoids is not a straightforward matter because of the mentioned variation in the content and composition of flavonoids in foods. Moreover, the variability and the lack of standardized analytical methods for their estimation further hinder the creation of compositional databases necessary to calculate flavonoids consumption. Intakes wUl also be affected by seasonal and regional availability of plant foods, as weU as by dietary habits dependant of cultural traditions and individual preferences. 

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