Quercetin is a flavonoid that occurs in many plant parts including rinds, barks, clover blossoms, and ragweed pollen. Capers are an especially rich source of quercetin. In 1962, S. Rangaswami and co-workers isolated it from Rhododendron cinnabarinum, a shrub that grows at high altitudes in Southeast Asia.
Quercetin’s bioavailability is poor, but its glycosides are readily absorbed by the body. It has been used to treat conditions ranging from eczema and inflammation to cancer and asthma. No clinical trials, however, have convincingly demonstrated its value; and it has not been approved by the US Food and Drug Administration for any use.
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