Quercetin and Psoriasis

A fellow employee suffers from severe psoriasis. She showed me an article this morning about treatment that she found in the newspaper. I have been thinking for sometime that she should be treating the condition internally as well as topically. She has tried various creams, ointments, salves, and presently uses light treatments. The article talks about several things, many of which I have heard about. However, one item that's talked about is quercetin. Can you please provide me with information about this? If nothing else, my curiosity has been aroused.

Quercetin is a water-soluble compound found in the leaves and flowers of certain plants. It belongs to a group of medicinally active plant pigments called flavonoids. Flavonoids have a wide range of known biological effects or activities, but some of the more significant for quercetin are: antioxidant, antihistamine, antiinflammatory, anticancer, and antiestrogenic. Among the many other wide ranging activities of quercetin is an antipsoriac effect.
According to Dr. Jim Duke's plant database at the U.S. department of agriculture, the top sources of quercetin in descending order are:
* evening primrose leaf (not the seed oil)
* sap of American mayapple
* onions and shallots
* tea leaf (probably green tea)
* rhizome of the Himalayan mayapple
Green tea contains about 1% quercetin. Evening primrose is remarkable in that the leaves contain 20% quercetin, the highest level recorded in plants. Evening primrose oil is a well-known source of essential fatty acids but the health benefits of the leaves are much less known. Evening primrose shoots gathered in the spring were once a favourite edible green for salads. According to herbalist John Lust in his book "The Herb Book" (available from Richters), evening primrose can be made into an ointment for skin rashes and irritations.