The red, blue, or violet colour of the skin of Vaccinium fruit is due to organic chemicals; and the anthocyanosides, which derive from these are the key to the beneficial effects of the fruit. At least 15 different anthocyanoside compounds have been identified from bilberry extracts. In addition there are up to 7% tannins, several alkaloids, twelve different phenolic acids and three glycosides which may all play a positive role for medicinal benefit.

The most effective medicinal use for bilberry/blueberry extract appears to be for improving micro-circulation, thus its effects on the capillaries serving the eyes, mucous membranes of the digestive and pulmonary systems.