Sunday October 12, 2008 (foodconsumer.org) -- A study published in the American Journal of Clinical Nutrition suggests oral supplement of flavonoids found in onions and tea may protect against cardiovascular disease.

The study led by Professor Kevin Croft from the University of Western Australia and colleagues found a daily dose of quercetin or (-)-epicatechin improved endothelial function.

Croft and colleagues tested a 200 mg dose of quercetin, (-)-epicatechin, or epigallocatechin gallate in 12 healthy men ages 43 years.

"These amounts were chosen as they represent a reasonable dose that could be achieved by eating flavonoid-rich foods such as chocolate, onions, and tea," the researchers said.

They found quercetin and (-)-epicatechinsignifcantly redued ET-1 blood levels, but only quercetin lowered urinary ET-1.

ET-1 is vasoconstrictors that narrow the blood vessels. The supplementation did not change NO or nitric oxide, a vasodilator that counteracts vasoconstrictors.