Flavonoids: Quercetin

Quercetin is a flavonoid, or chemical based in plants. Medical research has pinned quercetin as a focus of interest. Because of its antioxidant and anti-inflammatory effects, quercetin may one day be determined to work as an aid to fighting cancer.

Found in foods and available as a supplement, quercetin is used medicinally for patients with heart and circulation problems. It is also said to help patients with cataracts, hay fever, ulcers and gout.

Quercetin and Cancer

In the years of research to identify various types of flavonoids and their effects on disease, exciting findings involve quercetin. According to the Sloan-Kettering Cancer Center, quercetin ranks high in interest among the flavonoids, since it is the key source of bioflavonoids in the human diet. Moreover, scientists are always eager to find clues as to what chemicals found in nature might slow the growth of cancer cells.

Quercetin is believed to have potential for, if not eradicating cancer, at least slowing down the growth of cancerous cells. Recent studies suggest that quercetin may even have a beneficial effect on the body’s process of apoptosis, a dying-off process that eradicates defective cells.

The key breakthrough thus far has been research on the quercetin effect on prostate cancer. In 2001, media attention was focused on a Mayo Clinic study published in a leading cancer journal, “Carcinogenesis.” Quercetin blocked the growth of cancerous cells in that study.

Wait and See

You can get quercetin by eating some everyday foods, but it is also available in the form of pills. The American Cancer Society, however, would not want to see people of normal health spending money on quercetin supplements or changing their diet to accommodate high dosages. The ACS also notes that whlle quercetin studies look promising, it is too soon to be certain about cancer-fighting claims. Studies on quercetin so far have been performed on animals or on cell cultures in the lab. The ACS says more studies need to be done.


Study results have suggested that quercetin may fight sarcoidosis, an inflammatory disease, and asthma. It has also drawn interest in its potential to improve the condition of those who suffer from diabetes. Research has found that quercetin lowered levels of glucose in the blood. The study was performed on rats, not humans, but is certain to draw more attention in investigating the benefits of quercetin for diabetics.

Quercetin in Foods

You can find quercetin in many fruits and vegetables. Here is a sample list of food sources of quercetin according to food groups:

  • Fruits: Apples, red grapes, citrus fruits, raspberries, cranberries
  • Vegetables: Red onions, tomatoes, broccoli, leafy greens 
  • Others: Red wine, black tea, green tea, capers


Quercetin is available as supplements as well as in food, but you should always consult a doctor before resorting to supplements. Ample amounts of quercetin for normal functioning are available in foods. Since the Food and Drug Administration does not consider quercetin an essential nutrient, such as calcium or vitamin A, there is no FDA recommended intake to go by. As a supplement, the recommended dosage of quercetin varies depending on the ailment. If you think you might benefit, your doctor can advise you and recommend the right dosage.











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