Polyphenols are a large heterogenous group of chemicals, many thousand of which are found in plants. Vitamin E is a well known dietary polyphenolic substance, but others include stilbenes, chalcones and terpenes. Flavonoids are another group of polyphenols phytochemicals that include the flavones, flavonols, flavan-3-ols, anthocyanins, proanthocyanidins and flavanones. Evidence suggests that flavonoids may provide health effects in humans perhaps because of their gene regulatory and antioxidant effects. Higher intakes of flavonoids are associated with a reduction is some diseases, particularly cardiovascular disease and cancer. The reduced risk of oesophageal cancer in green tea drinkers for example, is ascribed to the high concentration of flavan-3-ol (catechin) flavonoids in tea. Evidence that flavonoids are antioxidants in humans and animals is convincing, and this is the most likely mechanism for their beneficial effects, although other effects are still being investigated.
Organic fruit may be a good source of flavonoids, particularly the skins of fruits such as apples, berries and pears. The reason for this relates to the role flavonoids play in the defence systems of plants against predators and pests. Flavonoids are secondary metabolites in plants, which means they are not required for survival of the plant, but are synthesised for other reasons. In the case of flavonoids, evidence suggests that they are synthesised in response to damage from predators and pests. Based on this understanding, it has been hypothesised that fruit exposed to more pests and predators may have higher levels of flavonoids in those areas, such as the skin, that are exposed. Studies seem to confirm this, with higher concentrations of flavonoids being found in the skin of fruits exposed to environmental stress. As a much smaller range of pesticides are used in organic agriculture, it is possible that the greater reliance on the plant’s own defence systems results in higher concentrations of flavonoids in their skins.
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