Adequate functioning of blood vessels is critical for general health and for optimal recovery in athletes. Blood vessels with greater ability to dilate can increase blood flow and thereby deliver more important nutrients and remove toxins from muscle in a more efficient manner. The most important substance in the body that causes dilation is nitric oxide (NO), and as a result there are a number of products on the market that are targeted at increasing NO bioavailability. Australian researchers have identified two dietary flavonoids that showed positive effects on NO. They studied healthy men who were given an oral dose of 200 mg of quercetin, epicatechin (EC), or epigallo-catechin (EGCG). Intake of both quercetin and EC resulted in increased markers of NO including plasma S-nitrosothiols, plasma nitrite, and urine nitrate concentrations. In addition, quercetin significantly decreased endothelin-1, a potent blood vessel constrictor. There were no effects of EGCG. These results point to a novel role of EC and quercetin as potential dietary supplements to augment NO bioavailability, and in the case of quercetin a method to decrease a strong vasoconstrictor.

Loke WM, Hodgson JM, Proudfoot JM, McKinley AJ, Puddey IB, Croft KD. Pure dietary flavonoids quercetin and (-)-epicatechin augment nitric oxide products and reduce endothelin-1 acutely in healthy men. Am J Clin Nutr. 2008 Oct;88(4):1018-25.