- Quercetin is a major flavonol, one of the almost 4,000 flavonoids (antioxidants) that occur in foods of plant origin, such as red wine, onions, green tea, apples, berries, and Brassica vegetables (cabbage, broccoli, cauliflower, turnips). Quercetin is also found in Gingko biloba, St. John’s wort, and American elder.
- Quercetin and rutin (another flavonol) are used in many countries as vasoprotectants (protects blood vessels) and are ingredients of numerous multivitamin preparations and herbal remedies. They occur mainly as glycosides, which means they are linked with various sugars. However, the ability of the body to absorb these compounds is questionable.
- Quercetin and other flavonols have a wide variety of biological effects, but the scientific evidence for use in the prevention or treatment of disease is weak. Quercetin has been considered as a therapy for cardiovascular diseases, high cholesterol, diabetic cataracts, inflammation, ischemic injury, chronic prostatitis, chronic venous insufficiency, gastrointestinal ulceration, hepatitis, allergies, asthma, viral infections, and hay fever.
- Review of the literature shows that there have been several studies on the association of quercetin and with the risk reduction for coronary heart disease and stroke, high blood pressure, cancers, and a few studies on other medical conditions. However, there is a lack of strong evidence to support any of these conditions.
Several of the effects of flavonoids that have been observed in laboratory and animal studies suggest that they might be effective in reducing cardiovascular disease risk. Studies in humans using polyphenolic compounds from red grapes showed improvement in endothelial function in patients with coronary heart disease. Antioxidant and cholesterol-lowering effects are proposed.
Population-based studies report that quercetin is associated with a reduced risk of coronary heart disease and stroke. Quercetin supplementation reduced blood pressure in hypertensive rodents and hypertensive humans.
|Immune function (after intense exercise)
Quercetin does not appear to affect changes in the immune system caused by intense exercise. However, it reduced the number of respiratory tract infections in people who participated in intense cycling. More research is needed.
|Pancreatic cancer prevention
Some research suggests that quercetin may help prevent pancreatic cancer in smokers. However, quercetin did not have this effect in non-smokers or former smokers. More research is needed to determine if quercetin is beneficial.
|Prostatitis/chronic pelvic pain syndrome
There is some evidence that quercetin may be useful for the treatment of chronic prostatitis and chronic pelvic pain syndrome. Further research is needed to confirm these results.
*Key to grades:
A: Strong scientific evidence for this use;
B: Good scientific evidence for this use;
C: Unclear scientific evidence for this use;
D: Fair scientific evidence against this use (it may not work);
F: Strong scientific evidence against this use (it likely does not work).
- Allergic rhinitis, allergies, anti-aging, antihistamine, anti-inflammatory, antioxidant, antispasmodic, anti-thrombotic, arthritis, antiviral, asthma, atherosclerosis (hardening of the arteries), autoimmune diseases, brain tumors, breast cancer prevention, cancer treatment, capillary fragility, cataract prevention, cerebrovascular disease, chronic venous insufficiency, coronary heart disease, cutaneous blood flux, diabetes mellitus, diarrhea (acute), depression, DNA damage, draft healing, eczema, edema, fibromyalgia, gout, hepatitis, herpes, high cholesterol, hives, ileostomy use, inflammation, interstitial cystitis, kidney toxicity, local anesthesia, lung problems, macular degeneration, mucosal mast cell inhibition, osteoporosis, peptic ulcers, platelet aggregation, prostate cancer prevention, protection against chemotherapy side effects, retinopathy, rheumatoid arthritis, schizophrenia, systemic lupus erythematosus (SLE), ulcers, vasoprotective, viral infections, vision problems (age-related).
Adults (over 18 years old)
- It has been suggested that quercetin should be taken 20 minutes before meals. Quercetin has been ingested from onions, juice, black tea, and red wine. Doses of 100-500 milligrams of quercetin have been taken 2-3 times daily. It is available in tablet, capsule, or softgel form. Intravenous and intramuscular forms have been injected by a healthcare provider.
Children (under 18 years old)
- Insufficient available evidence to recommend.
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