Scientists at the Institute of Food Research (IFR) have found that although the metabolites of quercetin - a common flavonol found in apples onions, tea and red wine - may reduce some of the early signs of heart disease, they are less effective than the compound itself. This illustrates the need for studies to concentrate on the effects of the compounds are found in the blood after the flavonoid has been ingested, absorbed and metabolised, rather than the flavonoid itself. "We tested compounds that are actually found in the blood, rather than the flavonoid in food before it is eaten, as only these compounds will actually come into contact with human tissues and have an effect on arterial health", said research leader Dr Paul Kroon. According to the scientists at the IFR, previous research has shown that quercetin is metabolised very quickly by the intestine and the liver and is not actually found in the blood. Consequently the team chose to focus on the metabolites and not the flavonoid itself. According to the researchers, it is one of only a few studies to do so. The research, published in the September issue of Atherolsclerosis, found quercetin and its metabolites may help prevent chronic inflammation leading to cardiovascular disease, via their effect on cells lining the blood vessels. Although the metabolites did have some effect on cells lining the blood vessels, it was lower than the effect of the parent compound, quercetin. "The effect is more subtle than laboratory experiments using the compound", said Dr Kroon. "But we can confirm that eating quercetin-rich foods may help prevent chronic inflammation leading to cardiovascular disease because the metabolites still have an effect on the cells lining the blood vessels", he said. A further finding from the study was that increasing the dose does not necessarily mean an increased effect. In fact, quite the opposite was seen in one of the inflammatory processes, where a lower dose had a larger impact. According to the scientists this lower dose was achievable through diet, for example by consuming 100-200g of onions. Flavonoids have been receiving increasing attention of late, with a mounting body of science, epidemiological and laboratory-based, suggesting a wide range of health benefits, including cancer-fighting potential, immune system benefits and cardiovascular health benefits. According to Business Insights, the market potential for flavonoids in the dietetic and nutritional supplement market is in excess of €670m for 2007, with annual increases of 12 per cent.