Quercetin is a ubiquitous flavonoid (flavonoids are natural compounds widely present in the plant world; they are secondary metabolites and perform numerous and important ecological functions, including the coloring of plants or their flowers and fruits, protection from UV rays, protection from some microorganisms, involvement as chemical messengers and as regulators of the cell cycle) present in a great variety of vegetables, including several fruits, such as grapes, apples, citrus fruits, in some vegetables, such as tomatoes, onions, broccoli, capers and in various plants, such as green tea, the Japanese Sophora (Styphnolobium japonicum (L.) Schot, syn. Sophora japonica L.) whose flowers are particularly rich in them, but also horse chestnut, ginkgo biloba, calendula, hawthorn, chamomile.

In nature, quercetin is not present in the isolated form but as an aglycone (portion of the non-sugar molecule) of various glycosides, including rutin and quercitrin.

Quercetin is extensively studied and used for its high antioxidant, anti-inflammatory and antiviral properties, which are widely demonstrated both in vitro and in vivo.

The quercetin molecule exerts its antioxidant effect as a scavenger of free radicals and is also able to counteract their production; the molecule has a certain cytoprotective action by entering the phospholipid bilayer of cell membranes, therefore protecting them from damage caused by reactive oxygen species.

Quercetin proved to be an anti-inflammatory molecule thanks to its ability to inhibit the progression of the arachidonic acid cascade, selectively inhibiting COX2 enzymes, reducing the production of prostaglandins (PGE2), a key protein in the inflammatory process; the molecule is also capable of controlling mast cell degranulation, inhibiting lipoxygenases and the synthesis of cytokines also involved in inflammatory processes.

Also known for its antiviral properties, quercetin is currently the subject of several studies for the treatment of patients with COVID-19.

The studies are clearly in the initial phase, but preliminary data are confirming its antiviral properties due to its ability to interfere with the virus replication process: the quercetin molecule destabilizes the protein (3CLpro) crucial for replication and therefore for the survival of the virus.


Quercetin is extracted and concentrated starting from the flowers of Sophora Japonica L. and is in a solid state, therefore ideal for all nutraceutical formulations, in particular in hard gelatin tablets and capsules; it is gluten-free and food-grade.

Quercetin, thanks to its proven antioxidant, anti-inflammatory and antiviral properties, is suitable for use in nutraceutical products intended to defend against the attack of free radicals, in the treatment of inflammatory conditions and in supporting the defenses against pathogens (maximum content / day: 200 mg, according to the indications of the Department of Health).

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Quercetin, Inflammation and Immunity – Nutrients. 2016 Mar 15;8(3):167. doi: 10.3390/nu8030167
Quercetin Directly Targets JAK2 and PKCδ and Prevents UV-Induced Photoaging in Human Skin – Int J Mol Sci . 2019 Oct 23;20(21):5262. doi: 10.3390/ijms20215262
Quercetin and Vitamin C: An Experimental, Synergistic Therapy for the Prevention and Treatment of SARS-CoV-2 Related Disease (COVID-19) – Front Immunol . 2020 Jun 19;11:1451. doi: 10.3389/fimmu.2020.01451. eCollection 2020.
A role for quercetin in coronavirus disease 2019 (COVID-19) – Phytother Res . 2020 Oct 9. doi: 10.1002/ptr.6887