Find out more about quercetin and how this potent antioxidant flavonoid offers significant therapeutic benefits against a wide range of conditions, from diabetes to DNA damage
Flavonoids are one of nature's many therapeutic gifts. Widely found in fruits and vegetables, these phenolic substances have antioxidant properties that protect cells from free radical damage.[i] One of the most well-known and studied flavonoids is quercetin, a flavonol mostly found in onions, berries, citrus fruits, broccoli and grapes.
A potent antioxidant, quercetin boasts of anti-inflammatory, anti-hypertensive, antiobesity and anti-atherosclerotic actions. Since free radicals figure into the development of diseases, quercetin holds promise for benefitting conditions such as high blood pressure, vascular disorders and metabolic syndrome.[ii] Here is compelling evidence of the health benefits of quercetin.
Potential Anti-Diabetes Aid
The development of Type 2 diabetes has been linked to oxidant stress caused by an unhealthy diet.[iii] Toona sinensis leaves, which are rich in quercetin, may reduce the risk of diabetes by reducing oxidative stress in the liver.
A topical compound containing substances such as quercetin, ascorbyl palmitate and vitamin D3 was formulated to reduce the oxidative stress contributing to peripheral diabetic neuropathy.[iv] A preliminary study in 2005 showed that the compound may safely relieve the symptoms of diabetic neuropathy and enhance quality of life.
Quercetin displayed protective effects in the kidneys and liver of obese animal models with Type 2 diabetes.[v] Together with quinic acid, quercetin also helped ameliorate hyperglycemia, hyperlipidemia and insulin resistance in diabetic rats.[vi]
Protection From DNA Damage
A 2011 study investigated the potential protective effects of quercetin against DNA damage and oxidative stress induced by methylmercury in animal subjects.[vii] For over 45 days, animal models were orally treated with methylmercury and the flavonoid with doses reflecting human exposure. The team then measured DNA damage in liver cells called hepatocytes and peripheral leukocytes (white blood cells).
The results revealed that methylmercury reduced the concentration of glutathione in the body by 17% and caused DNA damage to liver and blood cells. With quercetin, no such effects manifested. "In summary, our results indicate that consumption of quercetin-rich foods may protect mercury-exposed humans against the adverse health effects of the metal," the researchers wrote.[viii]
What makes this benefit particularly crucial is that the prevention of DNA damage is involved in preventing cancer via dietary compounds. An aqueous horseradish extract and its main flavonoids kaempferol and quercetin, for instance, demonstrated potential for DNA damage protection likely by acting as antimutagens.[ix]
Epidemiological studies vouch for the protective effects of phytochemicals against cancer risk. As a ubiquitous flavonoid, quercetin is an ideal candidate to fight cancer due to its antioxidant and antiproliferative actions.[x]
It is known to modulate a plethora of molecules for multitargeted cancer prevention and therapy. Here are examples of quercetin's chemopreventive abilities:
Quercetin exhibited a preventive effect on liver cancer in animal models.[xii] Hepatocellular carcinoma, the most common form of liver cancer, is on the rise in many countries, with an estimated 905,677 new cases globally in 2020.[xiii]
Quercetin inhibited tumor growth and enhanced the sensitivity to thermotherapy, indicating a potential treatment option for hepatocellular carcinoma.[xiv]
The combination of quercetin and ionizing radiation might be a promising therapy for colon cancer treatment through targeting colon cancer stem-like cells and inhibiting the Notch-1 signaling.[xv]
Quercetin suppressed the metastatic ability of lung cancer, with potential therapeutic applications for metastatic non-small cell lung cancer in particular.[xvi]
Prevention and Treatment of Various Infections
Quercetin may protect against the antibiotic-resistant Streptococcus pneumoniae infection mainly through inhibiting pneumolysin, a pore-forming cytotoxin and a major determinant of virulence.[xvii] Separate findings previously highlighted quercetin's therapeutic potential in treating sepsis as well.[xviii]
The flavonoid derivative quercetin-3β-O-D-glucoside (Q3G) also showed promising antiviral activity against two distinct species of Ebola, outbreaks of which occur frequently in African countries.[xix]
Hyaluronic acid, chondroitin sulfate, curcumin and quercetin taken together were also effective in preventing recurrent urinary tract infections in postmenopausal women.[xx]
Read more about scientific proof of the therapeutic value and significance of quercetin across numerous health issues and conditions in the nearly 600 abstracts with quercetin research found on the GreenMedInfo.com database.
[i] David A et al "Overviews of Biological Importance of Quercetin: A Bioactive Flavonoid" Pharmacogn Rev. 2016 Jul-Dec; 10(20): 84-89.
[ii] David A et al "Overviews of Biological Importance of Quercetin: A Bioactive Flavonoid" Pharmacogn Rev. 2016 Jul-Dec; 10(20): 84-89.
[iii] Zhang Y et al "Quercetin Isolated from Toona sinensis Leaves Attenuates Hyperglycemia and Protects Hepatocytes in High-Carbohydrate/High-Fat Diet and Alloxan Induced Experimental Diabetic Mice" J Diabetes Res. 2016 ;2016:8492780. Epub 2016 Nov 15.
[iv] Valensi P et al "A multicenter, double-blind, safety study of QR-333 for the treatment of symptomatic diabetic peripheral neuropathy. A preliminary report" J Diabetes Complications. 2005 Sep-Oct;19(5):247-53.
[v] Lai L et al "Protective effects of quercetin and crocin in the kidneys and liver of obese Sprague-Dawley rats with Type 2 diabetes: Effects of quercetin and crocin on T2DM rats" Hum Exp Toxicol. 2020 Oct 6:960327120954521.
[vi] Arya A et al "Synergistic effect of quercetin and quinic acid by alleviating structural degeneration in the liver, kidney and pancreas tissues of STZ-induced diabetic rats: a mechanistic study" Food Chem Toxicol. 2014 Sep ;71:183-96. Epub 2014 Jun 19.
[vii] Barcelos G et al "Protective properties of quercetin against DNA damage and oxidative stress induced by methylmercury in rats" Arch Toxicol. 2011 Feb 1. Epub 2011 Feb 1.
[viii] Barcelos G et al "Protective properties of quercetin against DNA damage and oxidative stress induced by methylmercury in rats" Arch Toxicol. 2011 Feb 1. Epub 2011 Feb 1.
[ix] Molecules. 2014 ;19(3):3160-72. Epub 2014 Mar 14. PMID: 24637991 www.greenmedinfo.com/article/aqueous-horseradish-extract-and-its-main-flavonoids-kaempferol-and-quercetin-h
[x] Priyadarsini R et al "The flavonoid quercetin modulates the hallmark capabilities of hamster buccal pouch tumors" Nutr Cancer. 2011 Feb 2:1. Epub 2011 Feb 2.
[xi] Caddeo C et al "Effect of quercetin and resveratrol co-incorporated in liposomes against inflammatory/oxidative response associated with skin cancer" Int J Pharm. 2016 Nov 20 ;513(1-2):153-163. Epub 2016 Aug 5.
[xii] Seufi A et al "Preventive effect of the flavonoid, quercetin, on hepatic cancer in rats via oxidant/antioxidant activity: molecular and histological evidences" J Exp Clin Cancer Res. 2009 ;28:80. Epub 2009 Jun 11.
[xiv] Dai W et al "Quercetin induces apoptosis and enhances 5-FU therapeutic efficacy in hepatocellular carcinoma" Tumour Biol. 2015 Dec 1. Epub 2015 Dec 1.
[xv] Li Y et al "Quercetin pretreatment enhances the radiosensitivity of colon cancer cells by targeting Notch-1 pathway" Biochem Biophys Res Commun. 2020 Jan 18. Epub 2020 Jan 18.
[xvi] Chang J et al "Quercetin suppresses the metastatic ability of lung cancer through inhibiting Snail-dependent Akt activation and Snail-independent ADAM9 expression pathways" Biochim Biophys Acta. 2017 10 ;1864(10):1746-1758. Epub 2017 Jun 23.
[xvii] Lv Q et al "Quercetin, a pneumolysin inhibitor, protects mice against Streptococcus pneumoniae infection" Microb Pathog. 2020 Mar ;140:103934. Epub 2019 Dec 17.
[xviii] Cui W et al "Quercetin Exerted Protective Effects in a Rat Model of Sepsis via Inhibition of Reactive Oxygen Species (ROS) and Downregulation of High Mobility Group Box 1 (HMGB1) Protein Expression" Med Sci Monit. 2019 Aug 4 ;25:5795-5800. Epub 2019 Aug 4.
[xix] Qiu X et al "Prophylactic efficacy of Quercetin-3-β-O-D-glucoside against Ebola virus infection" Antimicrob Agents Chemother. 2016 Jun 13. Epub 2016 Jun 13.
[xx] Torella M et al "Efficacy of an orally administered combination of hyaluronic acid, chondroitin sulfate, curcumin and quercetin for the prevention of recurrent urinary tract infections in postmenopausal women" Eur J Obstet Gynecol Reprod Biol. 2016 Dec ;207:125-128. Epub 2016 Nov 1.