Quercetin belongs to a group of plant pigments called flavonoids that give many fruits, flowers, and vegetables their color.
Flavonoids such as quercetin are antioxidants -- they scavenge damaging particles in the body known as free radicals, which damage cell membranes, tamper with DNA, and even cause cell death. Antioxidants can neutralize free radicals and may reduce or even help prevent some of the damage they cause. They also help keep LDL ("bad") cholesterol from being damaged, which scientists think may contribute to heart disease. In test tubes, quercetin has strong antioxidant properties, but researchers aren't sure whether taking quercetin (and many other antioxidants) has the same effects inside the body.
Quercetin acts like an antihistamine and an anti-inflammatory, and may help protect against heart disease and cancer.
Allergies, Asthma, Hay Fever and Hives
In test tubes, quercetin prevents immune cells from releasing histamines, chemicals that cause allergic reactions. On that basis, researchers think that quercetin may help reduce symptoms of allergies, including runny nose, watery eyes, hives, and swelling of the face and lips. However, there is no evidence yet that it works in humans.
Test tube, animal, and some population-based studies suggest that the flavonoids quercetin, resveratrol, and catechins (all found in high concentration in red wine) may help reduce the risk of atherosclerosis (plaque build up in arteries that can lead to heart attack or stroke). These nutrients appear to protect against the damage caused by LDL ("bad") cholesterol and may help prevent death from heart disease. However, most human studies have looked at flavonoids in the diet, not as supplements. Animal studies have used extremely large amounts of flavonoids (more than you could get through a supplement). More studies in people are needed to see if flavonoid supplements can be effective.
Test tubes studies show that quercetin prevents damage to LDL cholesterol, and population studies show that people who eat diets high in flavonoids have lower cholesterol. One study found that people who took quercetin and an alcohol-free red wine extract (which contains quercetin) had less damage to LDL cholesterol. More studies are needed, however, to show whether taking a quercetin supplement will have the same effect.
Studies show that quercetin supplementation reduces blood pressure in people who have hypertension.
Two small studies suggested that people with interstitial cystitis might benefit from flavonoids. People with this condition have bladder pain, similar to a bladder infection, and often experience an urgent need to urinate. In both studies, those who took a supplement containing quercetin appeared to have fewer symptoms. However, the studies included other flavonoids, so it isn't known which one might have the most beneficial effect. More and better-designed studies are needed.
Some preliminary evidence indicates that quercetin might reduce symptoms of prostatitis (inflammation of the prostate). One small study found that men who took quercetin had a reduction in symptoms compared to men who took placebo. The study was small, however, and the results need to be confirmed by other studies.
Rheumatoid Arthritis (RA)
There are reports of people with RA who had fewer symptoms when they switched from a typical Western diet to a vegan diet with lots of uncooked berries, fruits, vegetables, nuts, roots, seeds, and sprouts containing antioxidants, including quercetin. But there is no evidence that the positive effects were due directly to antioxidants, and no evidence that quercetin supplements will help treat RA.
Quercetin and other flavonoids contained in fruits and vegetables. Scientists have long considered important in cancer prevention. People who eat more fruits and vegetables tend to have lower risk of some types of cancer. And animal and test-tube studies suggest that flavonoids do indeed have anti-cancer properties. Quercetin and other flavonoids have been shown in these studies to inhibit the growth of cancer cells from breast, colon, prostate, ovarian, endometrial, and lung tumors. However, more research is needed.
Fruits and vegetables -- particularly citrus fruits, apples, onions, parsley, tea, and red wine -- are the primary dietary sources of quercetin. Olive oil, grapes, dark cherries, and dark berries -- such as blueberries, blackberries, and bilberries -- are also high in flavonoids, including quercetin.
Quercetin supplements are available as pills or capsules. They are often packaged with bromelain (an enzyme found in pineapple) because both are anti-inflammatories. Other flavonoid-rich extracts include those from grape seed, bilberry, Ginkgo biloba, and green tea.
There are also water-soluble forms of quercetin available, such as hesperidn-methyl-chalcone (HMC) or quercetin-chalcone.
How to Take It
There isn't enough evidence to recommend quercetin for children.
Recommended adult dosages of quercetin vary depending on the condition being treated. The following are guidelines:
- General supplementation: 100 - 250 mg 3 times per day
- Allergy symptoms: 250 - 600 mg per day divided in several doses
- Chronic prostatitis: 500 mg 2 times per day
- Interstitial cystitis: 500 mg 2 times per day
Do not exceed 1 g per day without talking to your doctor first.
Quercetin is generally considered safe. Side effects may include headache and upset stomach. Preliminary evidence suggests that a byproduct of quercetin can lead to a loss of protein function.
Pregnant and breastfeeding women and people with kidney disease should avoid quercetin.
At high doses (greater than 1 g per day), there are some reports of damage to the kidneys.
If you are being treated with any of the following medications, you should not use quercetin supplements without first talking to your health care provider.
Anticoagulants (blood thinners) -- Quercetin may enhance the effect of these drugs, increasing your risk for bleeding:
- Warfarin (Coumadin)
- Clopidogrel (Plavix)
Chemotherapy -- Test tube and animal studies suggest that quercetin may enhance the effects of doxorubicin and cisplatin, two chemotherapy medications used to treat cancer. In addition, some doctors believe taking antioxidants at the same time as chemotherapy can be harmful, while others believe it can be helpful. Talk to your oncologist before taking any supplements if you are undergoing chemotherapy.
Corticosteroids -- Quercetin may cause these drugs to stay in the body longer.
Cyclosporine -- Quercetin may interfere with the body's absorption of this drug, which is used to suppress the immune system.
Boots AW, Haenen GR, Bast A. Health effects of quercetin: from antioxidant to nutraceutical. Eur J Pharmacol. 2008;582(2-3):325-37.
Boots AW, Li H, Schins RP, Duffin R, Heemskerk JW, Bast A, Haenen GR. The quercetin paradox. Toxicol Appl Pharmacol. 2007;222(1):89-96.
Cai J, Nelson KC, Wu M, Sternberg P Jr, Jones DP. Oxidative damage and protection of the RPE. Prog Retin Eye Res. 2000;19(2):205-221.
Chan MM, Mattiacci JA, Hwang HS, Shah A, Fong D. Synergy between ethanol and grape polyphenols, quercetin, and resveratrol, in the inhibition of the inducible nitric oxide synthase pathway. Bio Pharm. 2000;60(10):1539-1548.
Edwards RL, Lyon T, Litwin SE, Rabovsky A, Symons JD, Jalili T. Quercetin reduces blood pressure in hypertensive subjects. J Nutr. 2007;137(11):2405-11.
Gates MA, Tworoger SS, Hecht JL, De Vivo I, Rosner B, Hankinson SE. A prospective study of dietary flavonoid intake and incidence of epithelial ovarian cancer. Int J Cancer. 2007 Apr 30; [Epub ahead of print]
Giuliani C, Noguchi Y, Harii N, Napolitano G, Tatone D, Bucci I, Piantelli M, Monaco F, Kohn LD. The flavonoid quercetin regulates growth and gene expression in rat FRTL-5 thyroid cells. Endocrinology. 2008;149(1):84-92.
Guardia T, Rotelli AE, Juarez AO, Pelzer LE. Anti-inflammatory properties of plant flavonoids. Effects of rutin, quercetin, and hesperidin on adjuvant arthritis in rat. Farmaco. 2001;56(9):683-687.
Hanninen, Kaartinen K, Rauma AL, Nenonen M, Torronen R, Hakkinen AS, Adlercreutz H, Laakso J. Antioxidants in vegan diet and rheumatic disorders. Toxicology. 2000;155(1-3):45-53.
Harwood M, Danielewska-Nikiel B, Borzelleca JF, Flamm GW, Williams GM, Lines TC. A critical review of the data related to the safety of quercetin and lack of evidence of in vivo toxicity, including lack of genotoxic/carcinogenic properties. Food Chem Toxicol. 2007 Jun 7; [Epub ahead of print]
Knekt P, Isotupa S, Rissanen H, Heliovaara M, Jarvinen R, Hakkinen S et al. Quercetin intake and the incidence of cerebrovascular disease. Eur J Clin Nut. 2000;54(5):415-417.
Kurowska EM, Spence JD, Jordan J, Wetmore S, Freeman DJ, Piche LA, Serratore P. HDL-cholesterol-raising effect of orange juice in subjects with hypercholesterolemia. Am J Clin Nutr. 2000;72(5):1095-1100.
Lamson DW, Brignall MS. Antioxidants and cancer III: quercetin. Alt Med Rev. 2000;5(3):196-208.
Longanga OA, Vercruysse A, Foriers A. Contribution to the ethnobotanical, phytochemical and pharmacological studies of traditionally used medicinal plants in the treatment of dysentery and diarrhoea in Lomela area, Democratic Republic of Congo (DRC). J Ethnopharmacol. 2000;71(3):411-423.
Mackraj I, Govender T, Ramesar S. The antihypertensive effects of quercetin in a salt-sensitive model of hypertension. J Cardiovasc Pharmacol. 2008;51(3):239-45.
Otshudi AL, Foriers A, Vercruysse A, Van Zeebroeck A, Lauwers S. In vitro antimicorbial activity of six medicinal plants traditionally used for the treatment of dysentery and diarrhoea in Democratic Republic of Congo (DRC). Phytomedicine. 2000;7(2):167-172.
Owen RW, Giacosa A, Hull WE, Haubner R, Spiegelhalder B, Bartsch H. The antioxidant/anticancer potential of phenolic compounds isolated from olive oil. Eur J Cancer. 2000a;36(10):1235-1247.
Owen RW, Mier W, Giacosa A, Hull WE, Spiegelhalder B, Bartsch H. Identification of lignans as major components in the phenolic fraction of olive oil. Clin Chem. 2000b;46(7):976-988.
Rakel D. Rakel Integrative Medicine. 2nd ed. Philadelphia, PA: Saunders Elsevier;2007.
Ramos S. Effects of dietary flavonoids on apoptotic pathways related to cancer chemoprevention. J Nutr Biochem. 2007 Jul;18(7):427-42. Epub 2007 Feb 23.
Ruiz PA, Braune A, Holzlwimmer G, Quintanilla-Fend L, Haller D. Quercetin inhibits TNF-induced NF-kappaB transcription factor recruitment to proinflammatory gene promoters in murine intestinal epithelial cells. J Nutr. 2007 May;137(5):1208-15.
Taepongsorat L, Tangpraprutgul P, Kitana N, Malaivijitnond S. Stimulating effects of quercetin on sperm quality and reproductive organs in adult male rats. Asian J Androl. 2008;10(2):249-58.
Thornhill SM, Kelly AM. Natural treatment of perennial allergic rhinitis. Alt Med Rev. 2000;5(5):448-454.
Xing N, Chen Y, Mitchell SH, Young CY. Quercetin inhibits the expression and function of the androgen receptor in LNCaP prostate cancer cells. Carcinogenesis. 2001;22(3):409-414.
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