Studies find that the dietary flavonoid quercetin – a potent antioxidant able to promote proper antihistamine and anti-inflammatory responses – may support cardiovascular, metabolic and respiratory health, and shows promise in the field of cancer research.
Quercetin is found in foods like apples, red onions, tea, red grapes, leafy-green vegetables and several kinds of berries. It’s the flavonoids that are responsible for the bright reds, yellows and oranges found in many of our plant foods. Of the more than 6,000 known flavonoids, quercetin is the one most often taken in supplement form.
Quercetin’s Role in the “French Paradox”
News stories have widely publicized the health benefits of drinking red wine. Scientists initially began looking at red wine as a possible explanation for the “French Paradox” – the observation that the French have a relatively low mortality rate from heart disease even though they smoke and eat diets high in saturated fats.(1) Studying 18 developed countries, researchers found a strong link between low heart disease mortality and wine consumption.(2)
The news reports attributed much of the health benefits from red wine to the polyphenol resveratrol. While red wine does contain resveratrol, it contains even higher levels of flavonoids – notably Quercetin – which has made some less-publicized, but no less-impressive news of its own.
Quercetin has long been known for its antihistamine and anti-inflammatory supporting properties. More recently, research has revealed that it may also help to promote longevity and protect against cardiovascular disease, metabolic syndrome, obesity, and cancer.
Let’s take a look at some of the science supporting the effects of this powerful little flavonoid.
Quercetin’s Effects on Allergies and Asthma
Quercetin acts as a natural antihistamine by helping prevent the release of histamine from mast cells and basophils (the culprit in hay fever’s itchy, watery eyes, runny nose, and sneezing, for example). A number of animal studies have been done to evaluate results of quercetin supplementation vis a vis asthma and allergic reactions. Here are just three examples:
• A South Korean study found that pretreating asthmatic mice with quercetin supported a significant inhibition of asthmatic reactions.(3)
• In a Brazilian study, all of the mice pretreated with quercetin were protected from fatal anaphylactic shock when challenged with an allergen, compared with 100% mortality in the untreated group.(4)
• A 2008 study using guinea pigs compared quercetin supplementation with prescription asthma medications. Quercetin supported a greater reduction of airway resistance than was achieved with the drug albuterol and as much as with the medications cromolyn and dexamethasone.(5)
Anti-inflammatory Benefits of Quercetin
The medical profession now knows that inflammation plays a part in virtually every chronic disease as well as many acute conditions. Quercetin is a powerful antioxidant that has been shown to promote the reduction of inflammation throughout the body.
• A 2007 study demonstrated how quercetin supplementation helped inhibit the production of pro-inflammatory cytokines associated with the mast cell-mediated allergic inflammation involved in diseases like rheumatoid arthritis, asthma and sinusitis. The researchers concluded, “Our study provides evidence that quercetin may [be] suitable for the treatment of mast cell-derived allergic inflammatory diseases.”(6)
• Serum C-reactive protein (CRP) is known to be a biomarker for chronic inflammation and a risk factor for a number of illnesses, including lupus and cardiovascular disease. Scientists at Michigan State University studied 8,335 adults to find out which foods could help lower serum CRP. They discovered that those who ate the most foods high in flavonoids had the lowest serum CRP levels. Of the flavonoids they studied, quercetin was at the top of the list for its ability to help the body protect against high serum CRP and thus protect against inflammation.(7)
Reducing the Risk of Cardiovascular Disease
Epidemiological studies have found that quercetin intake is associated with reduced risk of coronary heart disease and stroke.
• The oxidation of LDL has been recognized as playing an important role in the initiation and progression of atherosclerosis. In 2000, a study of 21 male subjects concluded that quercetin supplementaion can help the body inhibit LDL oxidation.(8)
• In 2007, University of Utah researchers conducted a randomized, double-blind, placebo-controlled, crossover study evaluating quercetin supplementation as a means of supporting lower blood pressure in hypertensive patients. Nineteen people with prehypertension and 22 people with stage 1 hypertension were given 730 mg of quercetin or a placebo. Although there was no change in blood pressure in the prehypertension group, there was a significant reduction in systolic, diastolic, and mean arterial pressure in the stage 1 hypertensive subjects who took quercetin.(9)
Quercetin’s Role in Metabolic Syndrome, Diabetes and Obesity
Current research is increasing the understanding of the role quercetin may play in helping to overcome obesity and managing metabolic syndrome – a group of risk factors that increase the risk for cardiovascular disease and type 2 diabetes.
• Spanish researchers undertook a study to analyze the effects of chronic administration of high doses of quercetin on metabolic syndrome abnormalities, including obesity, high cholesterol/ triglycerides, hypertension, and insulin resistance. Obese rats were given a daily dose of quercetin – either 2 mg/kg or 10 mg/kg of body weight – for 10 weeks. Both groups demonstrated improvements in cholesterol/triglyceride levels, hypertension and insulin resistance, but only those fed the higher dose produced anti-inflammatory effects and a reduction in body weight gain.(10)
• Several laboratory studies have demonstrated that quercetin may support the body’s ability to inhibit fat accumulation, surpress the growth of new fat cells, and trigger the programmed destruction of existing fat cells. One of the ways it works is by helping to block the uptake of glucose from the blood.(11-13) Interestingly, two of the studies discovered that adding resveratrol or resveratrol and genistein to the quercetin dramatically increased its ability to support reduced fat accumulation.(12, 14)
Promising Advances in Cancer Research
Scientists are interested in studying quercetin as a support for cancer prevention and even as a possible treatment component because of its ability to support the body’s ability to suppress cell proliferation and trigger programmed cell death.
• Experiments done in cell culture and animal studies have shown that quercetin can play a role in preventing or slowing tumor development in several different types of cancer, including breast, brain, pancreas, liver, and colon.(15-19)
• An early Phase I clinical trial of quercetin supplementation was conducted in the United Kingdom. It involved 51 participants who had a variety of different types of cancer. The results showed a decrease in the activity of the enzymes needed for tumor growth and evidence of antitumor activity. Additional clinical trials must be done before it can be determined whether quercetin might be a viable supportive option in treatment of cancer.(20)
Need-to-Know Facts About Quercetin
Quercetin with Bromelain: Bromelain is a protein-digesting enzyme, derived from pineapple stems, that is added to enhance the absorption of quercetin into the body. Bromelain is widely used in sports medicine to combat the discomfort and swelling of bruises, sprains, and muscle tears.
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Dosage: Recommended adult dosages range from 300 mg to 1,000 mg a day, usually divided into two or three doses. At very high doses, there have been some reports of damage to the kidneys, so it’s best not to take more than 1 gram (1,000 mg) per day without talking with your doctor.
– Do not take quercetin with bromelain if you are allergic to pineapple.
– May enhance effects of anticoagulants and increase risk of bleeding.
– May interfere with absorption of the immune suppressant cyclosporine.
– May cause corticosteroids to stay in the body longer.
– Consult a doctor before taking if you are pregnant, breastfeeding or have kidney disease.
Quercetin with its powerful “anti” properties – antioxidant, antihistamine, anti-inflammatory – may support cardiovascular, metabolic and respiratory health and shows promise in the field of cancer research.
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2. St Leger AS, et al. Factors associated with cardiac mortality in developed countries with particular reference to the consumption of wine. Lancet. 1979;1(8124):1017-1020.
3. Park HJ, et al. Quercetin regulates Th1/Th2 balance in a murine model of asthma. Int Immunopharmacol. 2008 Dec 2.
4. Cruz EA, et al. Immunomodulatory pretreatment with Kalanchoe pinnata extract and its quercitrin flavonoid effectively protects mice against fatal anaphylactic shock. Int Immunopharmacol. 2008 Dec 10;8(12):1616-21.
5. Moon H, et al. Quercetin inhalation inhibits the asthmatic responses by exposure to aerosolized-ovalbumin in conscious guinea-pigs. Arch Pharm Res. 2008 Jun;31(6):771-8.
6. Min YD, et al. Quercetin inhibits expression of inflammatory cytokines through attenuation of NF-kappaB and p38 MAPK in HMC-1 human mast cell line. Inflamm Res. 2007 May;56(5):210-5.
7. Chun OK, et al. Serum C-reactive protein concentrations are inversely associated with dietary flavonoid intake in U.S. adults. J Nutr. 2008 Apr;138(4):753-60.
8. Chopra M, et al. Nonalcoholic red wine extract and quercetin inhibit LDL oxidation without affecting plasma antioxidant vitamin and carotenoid concentrations. Clin Chem. 2000 Aug;46(8 Pt 1):1162-70.
9. Edwards RL, et al. Quercetin reduces blood pressure in hypertensive subjects. J Nutr. 2007 Nov;137(11):2405-11.
10. Rivera L, et al. Quercetin ameliorates metabolic syndrome and improves the inflammatory status in obese Zucker rats. Obesity (Silver Spring). 2008 Sep;16(9):2081-7.
11. Ahn J, et al. The anti-obesity effect of quercetin is mediated by the AMPK and MAPK signaling pathways. Biochem Biophys Res Commun. 2008 Sep 5;373(4):545-9.
12. Park HJ, et al. Combined effects of genistein, quercetin, and resveratrol in human and 3T3-L1 adipocytes. J Med Food. 2008 Dec;11(4):773-83.
13. Strobel P, et al. Myricetin, quercetin and catechin-gallate inhibit glucose uptake in isolated rat adipocytes. Biochem J. 2005 Mar 15;386(Pt 3):471-8.
14. Yang JY, la-Fera MA, Rayalam S, et al. Yang JY, la-Fera MA, Rayalam S, et al. Enhanced inhibition of adipogenesis and induction of apoptosis in 3T3-L1 adipocytes with combinations of resveratrol and quercetin. Life Sci. 2008 May 7;82(19-20):1032-9. Life Sci. 2008 May 7;82(19-20):1032-9.
15. Siegelin MD, et al. Quercetin promotes degradation of survivin and thereby enhances death-receptor mediated apoptosis in glioma cells. Neuro Oncol. 2008 Oct 29.
16. Choi EJ, et al. Antiproliferative effects of quercetin through cell cycle arrest and apoptosis in human breast cancer MDA-MB-453 cells. Arch Pharm Res. 2008 Oct;31(10):1281-5.
17. Vasquez-Garzon VR, et al. Inhibition of reactive oxygen species and pre-neoplastic lesions by quercetin through an antioxidant defense mechanism. Free Radic Res. 2008 Dec 29;1-10.
18. Tan S, et al. Quercetin is able to demethylate the p16INK4a gene promoter. Chemotherapy. 2009;55(1):6-10.
19. Warren CA, et al. Quercetin may suppress rat aberrant crypt foci formation by suppressing inflammatory mediators that influence proliferation and apoptosis. J Nutr. 2009 Jan;139(1):101-5.
20. Ferry DR, et al. Phase I clinical trial of the flavonoid quercetin: pharmacokinetics and evidence for in vivo tyrosine kinase inhibition. Clin Cancer Res. 1996 Apr;2(4):659-68.
* Karen Lee Richards is the Lead Expert specializing in Fibromyalgia and ME/CFS, for HealthCentral’s ChronicPainComnection (www.chronicpainconnection.com). Karen is co-founder of the National Fibromyalgia Association (NFA) and was Executive Editor of Fibromyalgia AWARE magazine for four years.
Note: This information has not been evaluated by the FDA. It is general and is not meant to prevent, diagnose, treat or cure any illness, condition or disease. It is very important that you make no change in your healthcare plan or health support regimen without researching and reviewing it in collaboration with your professional healthcare team.