Quercetin metabolites in lower dose range have anti-inflammatory protective effect on endothelial cells lining the blood vessels, and may protect against cardiovascular disease.

Scientists at the Institute of Food Research have found that flavonoid metabolites present in the blood after eating a flavonoid-rich meal may reduce some early signs of heart disease. The research is to be published in the journal Atherosclerosis, and is unique in that it focused on the natural compounds delivered to the blood after the intestines and liver metabolize dietary flavonoids. Much previous research has focused only on the “parent” flavonoids found in fruits and vegetables, assuming that once the original dietary flavonoid is metabolized, the metabolites had no beneficial effects in the body.

“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.

There are six classes of flavonoids: flavonols, flavones, isoflavones, flavanones, flavan-3-ols and anthocyanins. The scientists focused on the major flavonol in the diet, quercetin, the main sources of which are tea, onions, apples and red wine in the Western diet.

Previous IFR research has shown that quercetin is metabolized very quickly by the intestine and liver and is not actually found in human blood. For this study, Dr Kroon and his team analyzed the compounds that enter the bloodstream after quercetin is ingested, absorbed and metabolized and used them to treat cells in a simple model of atherosclerosis.

“The effect is more subtle than laboratory experiments using the parent 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,” said Dr Kroon.

The biological activity of flavonoids is highly dependent on their structure, and quercetin metabolites have very different activities from those of the parent compound.

“In order to assess the contribution of diets rich in fruit and vegetables to protect against cardiovascular disease, it is crucial that laboratory studies use the relevant compounds and most importantly, at concentrations achievable through diet,” said Dr Kroon.

This is one of very few studies that have used concentrations of quercetin metabolites that are achievable after eating quercetin-rich foods, such as onions. It was the first study to investigate all the major metabolites. It was possible because the scientists synthesized the exact compounds found in the blood after eating a quercetin-rich meal.

In the case of one inflammatory process, a lower dose actually had a larger impact. This indicates that if something is good for you, it does not necessarily follow that more is even better for you. Also, the lower dose was achievable through diet, for example by consuming 100 to 200 grams of onions.

Flavonoids are polyphenols naturally present in fruits and vegetables. People with high intakes of fruit and vegetables have been found to have a lower risk of cardiovascular disease and it was originally thought this was due to the antioxidant nutrients in plants. However, so far research has failed to observe any dramatically beneficial effects of the antioxidant vitamins in terms of preventing cardiovascular disease and recently interest has focused on the protective effect that dietary flavonoids (which can also be antioxidants) may have on the heart and blood vessels. IFR.ac.uk

Posted: 11|4|07 at 9:36 am. Filed under: News.