There are many members of this family, which can be found in the white part of citrus fruits just below the peel. They are important for blood vessel integrity and immune function. A high intake of flavonoids has been shown to lower heart attack risk1 and 500 mg a day (of the quercitin form) decreases the symptoms of prostatitis.
1Marniemi J. Dietary and Serum Vitamins and Minerals as Predictors of Myocardial Infarction and Stroke in Elderly Subjects. Nutr Metab Cardiovasc Dis. 2005 Jun;15(3):188-97. 43761 (10/2005)