Quercetin demonstrates blood sugar, insulin and lipid regulation; it is a powerful antioxidant with strong anti-inflammatory benefits; it is an antiviral and antimicrobial with multiple benefits against Diabetes, Alzheimer’s, blood pressure and cancer.
Quercetin is a natural flavonoid, a phytochemical and a class of polyphenols, found particularly in kale, apples, onions, capers, broccoli, cherry tomatoes and green tea, then blueberries, grapes, red wine, cherries, grains, nuts, and coffee. Sunlight stimulates the production of quercetin. Adults typically consume between 10 and 100 mg per day, largely depending upon their consumption of fruit and vegetables.
Quercetin is a lipophilic compound and therefore able to cross cell membranes and affect multiple pathways involved in illness and health (Updated from a 2010 review by Chris Woollams).
Quercetin, a very powerful antioxidant
Free radicals are dangerous molecules containing an unpaired electron which can literally rip pieces off other molecules in your body, damaging your cells. Because of the ‘double’ arrangement in the structure of the Quercetin molecule, it has twice the power to neutralise these free radicals. One review (1) describes it as an ‘outstanding’ antioxidant. It likely slows the aging process because of its power in reducing free radicals.
Quercetin, an anti-inflammatory
In a randomised, double-blind, placebo-controlled clinical trial (2) involving 50 women with Rheumatoid Arthritis, patients were given quercetin (500 mg/day for 8 weeks) or a placebo. The effects of the disease were significantly diminished, in particular for EMS, morning pain, and after-activity pain.
In a meta-analsis of blood pressure studies (17), there was a significant systolic and diastolic reduction in blood pressure with doses over 500 mg per day.
Quercetin, an antihistamine
Various studies have shown Quercetin to have various anti-allergic properties including the stimulation of the immune system, decrease in pro-inflammatory cytokines, and interleukin IL-4 suppression (3). It may be used for hay fever and other allergies. It may inhibit histamine release but, surprisingly, research with humans is limited. In lab tests it stabilised mast cells, known to release histamines.
Quercetin, an antiviral
As an antiinflammatory compound it has benefits with both viral and microbial infection. For example, Quercetin is a proven antiviral due to its ability to inhibit the initial stages of virus infection and its ability to block certain proteases important for viral replication (4). Benefits were shown with a variety of viruses from Herpes to HIV and even Coronavirus.
Quercetin and Diabetes
Quercetin has a positive effect on glycemia. In diabetes rat models, oral administration of Quercetin for 14–70 days resulted in a significant reduction in blood glucose by regenerating pancreatic islets, increased serum insulin levels and promoting insulin release. Quercetin also seems to promote glycogen synthesis, inhibit α-glucosidase activity and improve insulin resistance (5).
In another study (6) Quercetin was shown to have similar benefits to the type-2 diabetes drug Metformin. The conclusions stated, “Quercetin acts on multiple targets of diabetes and regulates key signalling pathways which improve the symptoms as well as the complications of Type 2 diabetes.”
Quercetin and Dementia (Alzheimer’s)
Quercetin, apart from its hypoglycemic benefits, is known to demonstrate hypolipidemic activities. In several in vitro studies, Quercetin has been shown to be neuroprotective - it protects neurons from oxidative damage while reducing lipid peroxidation.
Having antioxidant properties which protect the brain, it also inhibits the fibril formation of amyloid-β proteins, minimising cell breakdown and several important inflammatory cascade pathways. Quercetin supplementation also improves cognitive performance in Alzheimer’s (7).
Quercetin and Cancer
Cutting blood sugar and blood fats alone would make Quercetin a significant force in the fight against cancer. But it does more, starting with its strengths as a powerful antioxidant and anti-inflammatory.
Chronic inflammation and the development of free radicals are linked to an elevated risk of cancer and are known to increase cell proliferation, and cause direct damage to DNA, proteins, and lipids leading to carcinogenesis One would certainly expect Quercetin to be able to counter this (8). Quercetin has been shown to cause cancer cell cycle arrest. In vitro it has been shown to be very powerful against cancer, affecting many pathways. Quercetin also appears to bind to tubulin and would therefore be expected to bind to microtubules in cancer cells (9) and it has been shown to be a natural Tyrosine Kinase Inhibitor (10).
Although it has a significant number of studies and Reviews of studies, there is really little, if any, research with humans and cancer.
i) Breast cancer
In a study using mice after breast cancer injections, quercetin was shown to block the formation of blood supplies (angiogenesis) at a similar level to Tamoxifen. It achieved this by blocking the calcineurin pathway (11). In a review of the action of Quercetin in breast cancer (12), it states that quercetin leads to apoptosis via cytochrome C in the mitochondria; telomere structure can be influenced to stabilise DNA structure and Cancer Stem Cell generation may be suppressed; however the research is in the laboratory and/or with mice.
ii) Ovarian cancer
One study with mice showed significant results (13). Quercetin induced apoptosis via the mitochondria intrinsic and caspase-dependent pathways. It also caused mitochondria-mediated apoptosis and induced autophagy which normally has a protective role in ovarian cancer. Another lab study reported that quercetin decreased the viability and induced apoptosis of metastatic ovarian cancer cells.
iii) Lung Cancer
In one study, on NSCLC, Quercetin inhibited the migration/invasion of cell lines and cell invasion ability in bone metastasis in vivo (mice). Survival times of the animals also increased significantly after quercetin supplementation (14)
iv) Prostate cancer
Quercetin, as a powerful antiinflammatory compound, would seem a natural treatment for ‘highly inflammatory’ Prostate cancer. Again, the research is limited. A review suggested that Quercetin might prevent the initiation of prostate cancer as it indirectly blocks the activity of promoters of two important genes in the pathogenesis of prostate cancer i.e. androgen receptor and prostate specific antigen (PSA). Other studies have shown cytotoxic effects with the cancer cells not the healthy ones. The Quercetin effect on prostate cancer cells seems to be the detachment of Bax from Bcl-xL and the stimulation of caspase families (15).
v) Colorectal cancer
In the laboratory, Quercetin seems to inhibit the tumorigenesis of CRC via inhibiting the polarisation of M2 macrophages and downregulating hsa_circ_0006990 (16). It inhibited the proliferation of cancer cells and the migration.
Quercetin, Dosage
A typical dose is 500-1000 mg per day, but this does depend on what illness and whether you are trying to prevent or correct, and whether you are simultaneously taking drugs
Go to: Polyphenols - top foods for Health
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References
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Anticancer potential of quercetin: A comprehensive review; Abdur Rauf et al; Am Coll Nutr. 2017 Jan;36(1):9-15.
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The Effect of Quercetin on Inflammatory Factors and Clinical Symptoms in Women with Rheumatoid Arthritis: A Double-Blind, Randomized Controlled Trial; Fatemeh Javadi et al, Am Coll Nutr, 2017 Jan;36(1):9-15.
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Quercetin and Its Anti-Allergic Immune Response; Jiri Micek et al; Molecules, 2016 May 12;21(5):623
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Quercetin and its derivates as antiviral potentials: A comprehensive review; Amalia Di Petrillo et al; Phytother Res; 2022 Jan;36(1):266-278.
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In vitro and in vivo evidence that quercetin protects against diabetes and its complications: A systematic review of the literature; Guang-Jiang Shi et al; Biomedicine & Pharmacotherapy, Volume 109, January 2019, Pages 1085-1099
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Quercetin for managing type 2 diabetes and its complications, an insight into multitarget therapy; R Dhanya; Biomed Pharmacother. 2022 Feb;146:112560
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Neuroprotective Effects of Quercetin in Alzheimer's Disease; Haroon Khan et al; Biomolecules, 2019 Dec 30;10(1):59
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Role of oxygen free radicals in cancer development. Dreher D, Junod AF. Eur J Cancer. 1996;32a:30–8
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Perturbation of microtubule polymerization by quercetin through tubulin binding: a novel mechanism of its antiproliferative activity; Gupta K, Panda D. Biochemistry. 2002;41:13029–38
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Phase I clinical trial of the flavonoid quercetin: pharmacokinetics and evidence for in vivo tyrosine kinase inhibition. Ferry DR, Smith A, Malkhandi J, Fyfe DW, deTakats PG, Anderson D, et al. Clin Cancer Res. 1996;2:659–68
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Quercetin inhibits angiogenesis by targeting calcineurin in the xenograft model of human breast cancer; Xin Zhao et al; Pharmacol; 2016 Jun 15;781:60-8.
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A review on anti-cancer properties of Quercetin in breast cancer; Maryam Ezzati et al; Life Sciences, Volume 248, 1 May 2020,
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Quercetin induces protective autophagy and apoptosis through ER stress via the p-STAT3/Bcl-2 axis in ovarian cancer. Liu Y, Gong W, Yang ZY, Zhou XS, Gong C, Zhang TR, et al. Apoptosis. 2017;22:544–57.
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Quercetin suppresses the metastatic ability of lung cancer through inhibiting Snail-dependent Akt activation and Snail-independent ADAM9 expression pathways; Jer-Hwa Chang et al; Biochim Biophys Acta Mol Cell Res;. 2017 Oct;1864(10):1746-1758
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Emerging impact of quercetin in the treatment of prostate cancer; Soudeh Ghafouri-Fard et al; Biomed Pharmacother, 2021 Jun;138:111548.
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Quercetin Inhibits Tumorigenesis of Colorectal Cancer Through Downregulation of hsa_circ_0006990; Bin Chen et al; Front Pharmacol; 2022 May 18;13:874696
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Effects of Quercetin on Blood Pressure: A Systematic Review and MetaAnalysis of Randomized Controlled Trials;
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