What are flavonoids?

Flavonoids are polyphenols abundantly found in fruits, vegetables, and herbs (eg. tea, ginger root). Flavonoids are synthesized only in plants. They are a diverse group of phytochemicals, exceeding four thousand in number. From human nutrition perspective, flavonoids are important components of a healthy diet because of their antioxidant activity. Nevertheless, the antioxidant potency and specific effect of flavonoids in promoting human health varies depending on the flavonoid type (chemical, physical, and structural properties). Among the potent antioxidant flavonoid types are quercetin, catechins and xanthohumol. Flavonoid science is a research area rapidly gaining deeper insight on the health benefit and chemical property of flavonoids.

Flavonoids and Their Food Sources

Example of dietary flavonoid sources include:

Tea: Green, white or black tea are a rich source of flavonoids, especially flavonols (catechin, epicatechin, epigallocatechin, epicatechin gallate). Tea is a good source of quecertin.

Onions: The major flavonoid in onions is quercetin. Other flavonoids in onion are kaempferol and myricertin.

Honey: Depending on the flower type the bees feed on, honey contains myricertin, and quercetin.

Other dietary flavonoid sources are beans, spinach, buckwheat, strawberry, blueberry, rooibos plant. The concentration and composition of flavonoids in plants may vary depending on the growing condition, maturity, plant part, and variety.

Health Benefits of Flavonoids

Beneficial effects of flavonoids on human health are partly explained by their antioxidant activity. Because of the antioxidative property, it is suggested that flavonoids may delay or prevent the onset of diseases (such as cancer) induced by free radicals. They also inhibit low density lipoprotein (LDL) oxidation by free radicals. Flavonoids have been reported to have negative correlation with incidence of coronary heart disease. Furthermore, flavonoids have anti-bacterial, anti-viral, anti-tumor, anti-inflammatory, antiallergenic, and vasodilatory effect. They also inhibit platelet aggregation.


Verena, S., Mario Lorenz and Karl Stangl. 2006. The role of tea and tea flavonoids in cardiovascular health. Mol. Nutri. Food res. 50:218-228.

Subramani Sellappan and Casimir C. Akoh. 2002. Flavonoids and antioxidant activity of Georgia grown Vidalia onions. Journal of Agricultural and Food Chemistry, 50(19): 5338-5342.