Pharmacokinetics and metabolism of dietary flavonoids in humans.

Flavonoids are components of fruit and vegetables that may be beneficial in the prevention of disease such as cancer and cardiovascular diseases. Their beneficial effects will be dependent upon their uptake and disposition in tissues and cells. The metabolism and pharmacokinetics of flavonoids has been an area of active research in the last decade. To date, approximately 100 studies have reported the pharmacokinetics of individual flavonoids in healthy volunteers. The data indicate considerable differences among the different types of dietary flavonoids so that the most abundant flavonoids in the diet do not necessarily produce the highest concentration of flavonoids or their metabolites in vivo. Small intestinal absorption ranges from 0 to 60% of the dose and elimination half-lives (T1/2) range from 2 to 28h. Absorbed flavonoids undergo extensive first-pass Phase II metabolism in the small intestine epithelial cells and in the liver. Metabolites conjugated with methyl, glucuronate and sulfate groups are the predominant forms present in plasma. This review summarizes the key differences in absorption, metabolism and pharmacokinetics between the major flavonoids present in the diet. For each flavonoid, the specific metabolites that have been identified so far in vivo are indicated. These data should be considered in the design and interpretation of studies investigating the mechanisms and potential health effects of flavonoids.