NOW Foods' Quercetin is from a non-citrus source. This makes it quite suitable for persons with allergies, especially to citrus fruits.
Bromelain, a pineapple-derived enzyme, is added to enhance the absorption of Quercetin

Free Of:  sugar, salt, yeast, wheat, corn, milk, preservatives.
Other Ingredients:
Cellulose, Magnesium Stearate, Silica
S u p p l e m e n t   F a c t s
  Serving Size:   2 Vcaps
  Servings Per Container:   60
  -- Amount
Per Serving
% Daily
   Quercetin (as Quercetin Dihydrate) 800 Mg
   Bromelain (2,000 GDU) 200 Mg
 * Percent Daily Values are based on 2,000 calorie diet.     
  Daily Value not established.


Quercetin has been shown to be active against many types of cancer including: breast, prostate, colon, gastric, head and neck, leukemia, lung melanoma, liver, ovarian, cervical, rhabdomyosarcoma and it damages cancer cells only. In addition to its powerful antioxidant activity it is a potent aromatase inhibitor. Quercetin inhibits production of estrogen from DHEA and testosterone and also inhibits estrone sulfatase in the liver. It has anti-inflammatory effects and could help the muscle and joint pain associated with CFS. It also has strong anti-histamine activity and could improve the environmental and chemical sensitivities associated with CFS. It is immunostimulatory and antiviral against CMV, EBV, HIV, poliomyelitis and herpes simplex I & II. It blocks RNA transcriptase, impedes viral replication and increases reduced intracellular glutathione. Quercetin is non-toxic and the major flavonoid found in the US diet. It is estimated that Americans can consume approximately 25 mg/day. The therapeutic dose ranges from 2000 to 4000 mg/day.

excerpts from Quercetin - Resveratrol article by James South

Quercetin has also shown potent anti-cancer activity. Quercetin has "been shown to inhibit the growth of cells derived from human and animal cancers, such as leukemia and Ehrlich ascites tumors, the estrogen receptor-positive breast carcinoma (MCF-7), squamous cell carcinoma of head and neck origin, gastric cancer and colon cancer, as well as human leukemia HL-60 cells in culture [Vang et al reported resveratrol to be active in normalizing HL-60 cells in culture back into normal cells].... Quercetin has antiproliferative activity against breast and stomach cancer cell lines and human ovarian cancer primary cultures and can potentiate the action of [the anti-cancer drug] cisplatin ex vivo....
Hoffman et al in 1988 related both quercetin's direct anti-cancer activity, as well as its synergistic effect with several standard anti-cancer drugs to its ability to inhibit the enzyme protein kinase C. They also noted that Quercetin " a licensed [anti-cancer] drug in many countries, and is non-toxic at the required dose range." (20).

In his textbook Cancer & Natural Medicine, J. Boik reports the importance of platelet aggregation and eicosanoid issues in cancer. Thus he writes: "The importance of platelet aggregation in cancer metastasis is more widely accepted.... Activated platelets are sticky and may enhance the adhesion of tumor cells to the endothelial lining. Platelet-secreted factors... may stimulate the growth of tumor cells and contribute to their survival within the blood circulation. Experimental studies have shown that migrating cells from some cancers induce platelet aggregation by modifying the eicosanoid balance.... Tumors promote platelet aggregation by stimulating the production of PGI2.... Tumors synthesize eicosanoids through both the [COX and LOX] pathways. The [LOX] pathway of [AA] is important, if not essential, to tumor promotion." (23). Given the prior discussion in this article of resveratrol as premier COX-inhibitor and quercetin as premier LOX-inhibitor, and both as excellent anti-platelet aggregators, their combined potential anti-cancer benefit should be evident.

Hollman, et al recently completed a study of Quercetin absorption in healthy ileostomy patients with complete small intestines. They found a 100mg dose of pure Quercetin to be absorbed approximately 24%. (24).

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