More research needed into effects of flavonoids and flavonoid-rich food sources on heart disease

More research is needed into food compounds which could reduce the risk of heart disease, according to a systematic review of trials carried out so far.

Dr Lee Hooper from the University of East Anglia (UEA) led a group of scientists who analysed 133 studies on the effects of flavonoids and flavonoid-rich food sources on heart disease related risk factors.

It is known that consuming certain foods may reduce the risk of cardiovascular disease and increased attention is being focused on flavonoids, a diverse group of compounds that occur naturally in many commonly consumed fruits, vegetables, herbs, grains and drinks.

The health benefits associated with flavonoids were reported as early as 1930, but limited data and a small number of studies have made it difficult for scientists to make specific recommendations regarding flavonoid consumption and health.

The review, thought to be the first of its kind, was carried out to gain a better understanding of which flavonoids and flavonoid-rich foods are most beneficial to human health and identify priorities for future research. It involved scientists from UEA, the Institute of Food Research, the Harvard School of Public Health, the Heart Research Institute and Kings College London. The results are published in the July issue of the American Journal of Clinical Nutrition.

While the analysis confirmed differential effects among flavonoid subclasses and flavonoid-rich foods, it found significant research gaps for some common subclasses, such as anthocyanins and flavanones.

Acute and chronic consumption of chocolate or cocoa increased flow-mediated dilation, an indicator of vascular blood flow, and reduced blood pressure. However there was no evidence that chocolate or cocoa had an effect on low-density lipoprotein (LDL) - the 'bad' cholesterol - concentrations. The effects of different soy sources on blood pressure also varied. Acute intake of black tea increased blood pressure, whereas that of green tea significantly reduced LDL cholesterol.

Dr Hooper, from the School of Medicine, Health Policy and Practice, said the review highlighted the need for studies that explain the role of individual flavonoids and the relevant effects on heart disease risk factors.

"This next step will advance flavonoid research and help determine optimal doses or specific food sources required to reduce heart disease risk. Meanwhile existing data suggests that consuming a variety of flavonoid-rich food sources - aiming for 5 portions of fruit and vegetables daily - will be beneficial to our health."

The results of the review come as researchers at UEA embark on a study to find out whether flavonoids in cocoa reduce heart disease risk in women with diabetes. Postmemopausal women with type 2 diabetes will be asked to eat a bar of specially formulated chocolate every day for a year. It will provide a higher dose of the protective compounds than found in standard chocolate, while soy has also been added to maximise the potential benefits.

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