Quercetin shows antioxidant effects by scavenging free radicals directly and affecting the pathway of oxidative stress. Experimental results suggested that Quercetin scavenging activity on hydroxyl radical (·OH) was 89.3% (concentration: 50μM), 5.2 times as large as that of vitamin C. On an in vitro model, FRAP value for reducing power was 4.2 mmol Fe² + /g, 37% greater than general antioxidants like quercetin. A 2021 study published in the Journal Antioxidants demonstrated that Quercetin was able to decrease the formation of malondialdehyde (MDA) by 62% (concentration 100μM) in lipid peroxidation inhibition (TBARS method), which is superior to the 48% effect of alpha-tocopherol.
Another mechanism is metal ion chelation. Quercetin possesses a chelation constant (log K) of 5.8 for Fe² +, suppressing 90% of Fenton reactions (iron-catalyzed ·OH generation) at pH 7.4, and consequently reducing oxidative DNA damage. In the clinical trial (NCT04594254), it was found that the patients receiving 500mg per day of Quercetin experienced a 28% reduction in serum ferritin levels and a 41% reduction in the oxidative stress marker 8-OHDG after 8 weeks. This compound is applied in the food market to prevent oil racidity, and adding 0.02% Quercetin can decrease the peroxidation value (PV) of rapeseed oil from 12.3 meq/kg to 4.1 meq/kg, and prolong the shelf life to 180 days (90 days only in the control group).
Quercetin upregulates the cellular defense system by stimulating the Nrf2-ARE pathway. Animal models have established that Quercetin dose of 50mg/kg is capable of increasing liver SOD activity by 65% and GSH level by 52%. Quercetin (20μM) in UV-irradiated human skin fibroblast models reduced MMP-1 expression by 73% and collagen synthesis by 38%. This mechanism has been applied to anti-aging skin products, and one brand of serum with 1% Quercetin enhanced skin elasticity by 21% after 28 days in a third-party test (Cutometer MPA580 measurement).
Inhibition of activating enzymes is one key method. Quercetin inhibits xanthine oxidase (XO) with an IC50 value of 3.2μM, 58% lower than allopurinol, which can reduce uric acid and superoxide anion production. In a model of gout, 100mg/kg Quercetin reduced levels of the joint inflammation factor IL-1β by 66%, an action equivalent to colchicine but without toxicity to the kidneys. In 2023, Quercetin was approved by the European Union (EFSA) as a food additive (E number E161b), to be used to add to beverages up to 0.05g/L, which experimentally has been demonstrated to inhibit 80% oxidation of nitrite (in conditions of gastric fluid).
A synergistic effect increases antioxidant activity. With vitamin C (molar ratio 1:2), Quercetin boosted the clearance rate of DPPH free radicals from 78% to 94%, as the oxidized vitamin C was regenerated by Quercetin with an efficiency of 92%. A sports supplement brand took the “500mg Quercetin+1g vitamin C” formula, and clinical trials found that the exhaustion time of athletes was extended by 19%, and muscle injury marker CK-MB decreased by 33%. In the cultivation of agricultural production, 0.1% Quercetin with chitosan treated strawberries, after storage in the fridge for 14 days, the decay rate decreased from 28% to 7%, and anthocyanin retention rate increased to 91%.
Cell membrane protection capacity was established through quantitative evidence. Quercetin (10μM) reduced RBC hemolysis rate from 25% to 6% (H₂O₂ model), and membrane fluidity (as measured by fluorescence polarization method) increased to 0.28 (control group 0.35, lower the better for fluidity). In a cell model of Parkinson’s disease, preconditioning with Quercetin increased dopaminergic neuron survival to 79% from 38%, and mitochondrial membrane potential recovered to 85% of the control group. Industrial application scenario: A Quercetin coated health supplement, the bioavailability was enhanced to 32% (that of the standard preparations being only 5%) whereas for once oral dosing peak in plasma was found to be 1.2μg/mL with extended half life to 6.8 hours.
Its wonderful neutralization on environmental toxins. Quercetin has dose-dependent effects in protecting against oxidative injury caused by PM2.5 in lung cells, suppressing ROS generation by 82% at a dose of 50μM. In cadmium-treated liver cells, Quercetin (20μM) restored the activity of GSH-Px enzyme to 76% of normal value, and the rate of cadmium chelation was up to 63%. In accordance with this, a maker of an air purifier applied Quercetin over a HEPA filter, and the test confirmed that the decomposition rate of formaldehyde was as high as 41% to 89% compared to a normal filter, and remained active for 1,200 hours.
Economy and security supports are widely utilized. The Quercetin API price is about 220/kg (≥952.2-22 purity). Toxicology tests demonstrated LD50 (oral rat) > 2000mg/kg, mutagenic test (Ames test) negative. The FDA in 2022 certified Quercetin as a GRAS (generally regarded as safe) ingredient to be used as a dietary supplement in an upper limit dose of 1,000 mg/day. The world market figures in 2023 placed the total sales of Quercetin allied products at 120 million and projected the compound to rise with an average annual growth rate of 11.3% in 2025, where over 60% was taken by anti-aging and sports nutrition.
