Quercetin is best known for its effectiveness in treating asthma and
allergies as well as its ability to fight viruses and inflammation. While these
uses are fairly well established, you may have heard that quercetin can do far
more, such as prevent strokes or fight cancer. Outlined below is what the
research has shown on quercetin and why it is an effective remedy, and how you
can obtain it.
To date, studies on quercetin have been very positive, showing that high
dietary intake of quercetin may lower your risk for stroke and cardiovascular
disease. There is evidence that quercetin has bone-building effects, which may
make it a useful therapy for countering osteoporosis. Quercetin also appears to
fight ulcers—it has been shown to inhibit the growth of
the bacteria responsible for most stomach and small intestine ulcers. Other
research has shown quercetin to be a potential aid to HIV treatment, and yes,
quercetin even shows promise as a cancer therapy: studies report quercetin
appears to kill cancer cells in certain cancers, including squamous cell
cancers, leukemia, and cancers of the breast, lungs, ovaries, and colon. Of
course, all of these study results need to be confirmed by further studies and
Quercetin is one of the bioflavonoids, the antioxidants that give color to
fruits, vegetables, and flowers. Bioflavonoids help to keep blood vessels strong
and to repair cartilage, tendons, and ligaments. Quercetin has the greatest
antioxidant effect of all of the flavonoids. When it comes to battling asthma,
quercetin has healing properties that nonsteroidal anti-inflammatory drugs
(NSAIDs) and antihistamines lack—by repairing
tissues, fibers, and membranes, it strengthens the entire respiratory system. In
addition to relieving symptoms, quercetin decreases allergies and respiratory
symptoms over time by regenerating tissues.
Where can you find quercetin? Foods with the highest levels of quercetin
include onions, apples, red wine, tea, green tea, spices, and to a lesser extent
green leafy vegetables and beans. Most people consume about 25 to 50 mg of
quercetin daily. Healthy people can safely increase their intake to 250 to 1,000
mg daily. For chronic allergy, pain, inflammation, asthma, or sinusitis, take
500 to 6,000 mg daily, divided into several doses. Keep in mind that quercetin
supplements come in various forms, and some are more usable by the body than
others. Quercetin dihydrate is the most easily used by the body, followed by
quercetin chalcone. In contrast, other quercetins, such as hesperidin, rutin,
and rosehip, are far less effective.
Be sure to talk with your physician or pharmacist to determine whether
quercetin might be beneficial for you. Some supplements should not be taken if
you have certain medical conditions or are taking particular prescription
Nonsteroidal anti-inflammatory drugs (NSAIDs): A large class of drugs
commonly used to relieve pain, reduce inflammation, and lower fevers. Side
effects may include stomach upset and intestinal bleeding. Ibuprofen is a common
Squamous cell cancer: Cancer in the form of a slow-growing tumor that
is often found on the skin and has been caused by overexposure to the sun.
Squamous cell cancer may also occur in the lungs, larynx, nose, bladder, anus,
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Kandaswami C, Perkins E, Drzewiecki G, Soloniuk DS, Middleton E Jr.
Differential inhibition of proliferation of human squamous cell carcinoma,
gliosarcoma and embryonic fibroblast-lung cells in culture by plant flavonoids.
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Kandaswami C, Perkins E, Soloniuk DS, Drzewiecki G, Middleton E Jr. Ascorbic
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Keli SO, Hertog MG, Feskens EJ, Kromhout D. Dietary flavonoids, antioxidant
vitamins, and incidence of stroke: the Zutphen study. Arch Intern Med.
Le Marchand L, Murphy SP, Hankin JH, Wilkens LR, Kolonel LN. Intake of
flavonoids and lung cancer. J Natl Cancer Inst. 2000;92(2):154-160.
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Ranelletti FO, Maggiano N, Serra FG, et al. Quercetin inhibits p21-RAS
expression in human colon cancer cell lines and in primary colorectal tumors.
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Sziklai I, Ribari O. Flavonoids alter bone-remodeling in auditory ossicle
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