Written by Marcia J. Egles, MD.
Flavonoids are a diverse family of compounds made by plants. Over 4,000 flavonoids have been identified. Important dietary sources of these micronutrients include cocoa, tea, apples, berries, citrus, soy and red wine. Flavonoids may contribute to some of the health benefits associated with diets rich in fruits and vegetables (1). A reduced risk of cardiovascular disease has been reported in persons with high flavonoid intakes (2).
In the test tube, the anti-oxidant activity of flavonoids can be demonstrated. However, in the human diet, flavonoids are absorbed in small amounts. That which is absorbed is quickly eliminated from the body. Thus, the anti-oxidant activity of flavonoids within the human body may be negligible.
Other studies have shown that consumption of flavonoid-rich foods is associated with improvement in blood pressure and other measures of cardiovascular health (3, 4). This action within the body may be occurring within the lining of blood vessels.
A recent study gives evidence that flavonoids might be the active agents involved. Twelve healthy Australian adult men, ages 39 to 47, participated in the four- week study. The men took no medications or vitamin supplements and consumed a flavonoid-restricted diet. Each week, the men came to a clinic visit and received either water or one of the three flavonoids dissolved in water. More specically, they each received, in a random order, a 300 milliliter drink of one of the following: water (control), 200 milligrams of quercetin dissolved in water, 200 milligrams of (-)-epicatechin in water, or 200 milligrams of epigallocatechin gallate in water. The amounts of flavonoids consumed in the drinks were designed to be comparable to amounts found in flavonoid- rich foods.
On each treatment day, blood and urine samples were collected prior to the drink. A second blood sample was taken two hours later, and a five hour urine sample collected. The blood and urine samples were analyzed for the presence of the flavonoids and their metabolites, markers of vascular activity, as well as markers of oxidative stress.
Significant changes in markers of vascular activity were found with two of the flavonoids, quercetin and (-)-epicatechin. None of the three treatments revealed any anti-oxidant activity.
Quercetin-rich foods include apples and onions. Cocoa is a source of (-)-epicatechin. Per 100 gram servings, raw apples with skin contain about 5 milligrams of quercetin, and raw red onions about 20 milligrams. A 100 gram portion of dark chocolate provides 40 milligrams of (-) epicatechin. (5)
Source: Loke, Wai Mun, et al. “Pure dietary flavonoids quercetin and (−)-epicatechin augment nitric oxide products and reduce endothelin-1 acutely in healthy men.” The American journal of clinical nutrition 88.4 (2008): 1018-1025.
© 2008 American Society for Nutrition
Posted May 7, 2010.
References:
- Review of flavonoids: found on the Oregon State University website.
- Huxley RR, Neil HAW. The relation between dietary flavonol intake and coronary heart disease mortality: a meta-analysis of prospective cohort studies. Eur J Clin Nutr 2003;57:904.
- Stein JH, Keevil JG, Wiebe DA, Aeschlimann S, Folts JD. Purple grape juice improves endothelial function and reduces the susceptibility of LDL cholesterol to oxidation in patients with coronary artery disease Circulation1999;100:10505 .
- Hodgson JM, Burke V, Puddey IB. Acute effects of tea on fasting and postprandial vascular function and blood pressure in humans. J Hypertens 2005;23:4754.
- USDA Database for the Flavonoid Content of Selected Foods – 2003 found on the USDA website.
