Quercetin is a naturally occurring phytochemical which has many promising bioactive effects. The antidiabetic, anti-inflammatory, antioxidant, antimicrobial, anti-Alzheimer’s, antiarthritic, cardiovascular, and wound-healing effects of Quercetin have been extensively investigated, as well as its anticancer activity shown against different types of cancer cells. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10384403/
Quercetin and its derivatives are found in many common foods, and people can benefit from their protective effects by ingesting them in their diet or as a food supplement. Quercetin nanoparticles also appear as a promising way  to enhance the bioavailability of other antioxidant substances and medications.
This present review provides a brief overview of the known therapeutic effects, and areas of interest which may provide new insights, and lead to new research on Quercitin.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7254783/
Quercetin is an antioxidant flavonol belonging to the flavonoid group, and gives color to vegetables, and fruits. Its main sources are grapes, berries, cherries, apples, citrus fruits, onions, buckwheat, kale, tomatoes, red wine, and black tea.
Scientific study has shown that Quercetin is an even more powerful antioxidant than vitamins C and E https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5214562/
Quercetin exerts a marked effect on the immunity and inflammation.



Quercetin has been used therapeutically for situations characterized by severe inflammation as occurs in the phenomenon known as the cytokine storm that can be a  part of the life threatening illness that may accompany a SARS-Covid infection and inflammatory pneumonia []. The acute lung damage and multiple organ failure phenomena that may occur may be helped by quercetin.


There are numerous studies on Quercetin and its potential as an anti-hypertensive agent. In one placebo-controlled double-blind study, 730 mg of Quercetin daily given for 28 days caused significant reductions in systolic and diastolic arterial pressures  in hypertensive patients.
One important action is its benefit to the endothelial layer of blood vessels. Endothelial dysfunction is tied to many of the pathological and health destroying properties of cardiovascular disease. Endothelial dysfunction is characterized by an increase in oxidative stress and impaired nitric oxide production which is a known consequence of hypertension. Quercetin  promotes nitric oxide bioavailability by increasing endothelial nitric oxide synthesis and also inhibiting the activity of enzymes that degrade nitric oxide. []. Quercetin also exerts antioxidant properties by destroying free radicals and decreasing oxidative stress. This helps the proper functioning of the endothelial cells and protects them from further damage which occurs in hypertensive states. Quercetin therefore promotes vasodilation, reducing vascular resistance, and lowering blood pressure [].


Quercetin and related flavonoids inhibit the release of histamine from mast cells , an important mechanism involved in allergic type reactivities of all kinds[]. Also, Quercetin and related flavonols suppress the release of the inflammatory markers interleukin (IL)-4 and IL-13 production which are released by anti-IgE antibody-stimulated cells, such as mast cells or basophils.


Acute  asthma is characterized by an eosinophilic response and its consequent  inflammation, which occurs with an increase in mucus output, and the hyperresponsiveness of the airways []. Quercetin, has been shown to have anti-asthmatic effects which may interfere with the development and persistence of wheezing and airway obstruction which occurs. In this condition airway edema (swelling of surrounding tissues) , increased mucus secretion, the increase in eosinophils, and systemic immunoglobulin E (IgE) production, may all be beneficially affected by Quercetin [].  Numerous studies have identified the pathways whereby Quercetin shows its potent anti-inflammatory and antioxidant properties which suppress production of the inflammatory cytokines that play a crucial role in asthma []. In this situation quercetin reduces airway hyperresponsiveness, eosinophilic inflammation, and the excess secretion of  mucus[].

Beneficial Effects on Diabetes Complications

Quercetin has been shown to improve glucose metabolism and the body’s ability to produce insulin secretion.  Studies have shown that Quercetin may be a promising target for drug  development as it enhances insulin sensitivity and reduces insulin resistance. It is also felt that the many properties that Quercetin has been shown to have may help to prevent diabetes and its complications via reducing oxidative stress.

Beneficial Effects on Diabetic Liver Disorders 

Quercetin may prevent oxidative damage to the liver.

Beneficial Effect on Diabetic Nephropathy (kidney damage) Quercetin ameliorates oxidative stress in renal tissues.

Diabetic Retinopathy 

Diabetes-induced diabetic retinopathy occurs mainly due to oxidative stress, inflammation, and damaged retinal blood vessels. .  Quercetin has been shown experimentally to to reduce

VEGF (vascular endothelial growth factor) expression. , a mechanism involved in blood vessel proliferation. Quercetin may exerted a protective effect against retinal neurodegeneration by reducing oxidative damage and  inflammation, and inhibiting the neuron apoptosis.

Effect on Cardiovascular Disease

 Overweight or obese subjects ranged between 25 and 65 years were exposed to a double-blind study of 6 weeks to examine the effects of Quercetin (150 mg Que daily).

This study showed anti-inflammatory properties in patients with coronary artery disease (CAD).

A 10-week double-blind randomized clinical study of  72 females with type 2 diabetes, were given either a placebo or 500 mg capsules of Quercetin daily. Those given Quercetin reduced systolic blood pressure and also reduced total cholesterol levels, LDL, and triglyceride levels. The levels of the inflammatory markers TNF-α and IL-6 were also lowered.

Effect on Alzheimer’s Disease

Quercitin is being used and studied for its potential therapeutic benefit in resistance to the development of dementia/Alzheimer’ disease. It has documented neuroprotective effects against oxidative stress .  A number of mechanisms may be in play here including amyloid-β (Aβ) aggregation inhibition, intracellular neurofibrillary tangles formation inhibition, amyloid precursor protein  inhibition, cleaving enzyme inhibition, acetylcholinesterase inhibition.

Reduced cholinergic neurotransmission is known as an early symptom of Alzheimer’s disease. Quercetin may counter this reduction. 


Effect on Arthritis

Arthritis is associated with decreased motion and flexibility, and its symptoms include swelling, pain, stiffness, and redness. There are many types of arthritis, the most common being osteoarthritis, gout, and rheumatoid arthritis. Treatment of arthritis often includes steroids, and nonsteroidal anti-inflammatory drugs.,  The side effects of a prolonged use of steroids may be severe and among other problems may lead to worsening of the osteoporosis itself, as well as susceptibility to fractures. Chronic use of nonsteroidal anti-inflammatory drugs can lead to stomach ulcers and kidney damage. Chronic joint inflammation may lead to the destruction of a joint,  requiring surgical intervention by a joint replacement .

Quercetin may reduce the  pain and inflammation associated with arthritis.  It inhibits joint pain and  edema, without the adverse effects on other organs described as medication side effects. Quercetin’s protective  mechanisms include inhibiting of oxidative stress, cytokine production, COX-2 production, and other biochemical benefits.

Quercetin has been considered as an adjunctive treatment for rheumatoid arthritis. The administration of Quercetin has been shown to be effective when given with methotrexate to reduce joint inflammation . The mechanisms included reduction of TNF-α, IL-1β, IL-17, and monocyte chemoattractant protein-1 levels.

Anticancer Effects

Many reports were detected on the anticancer activity of Que, and they are summarized in the published report entitled, “Quercetin and epigallocatechin gallate inhibit glucose uptake and metabolism by breast cancer cells…” it  is stated , “Our results implicate QUE and EGCG as metabolic antagonists in breast cancer cells, independently of estrogen signalling, and suggest that these flavonoids could serve as therapeutic agents/adjuvants even for ER-negative breast tumors.”https://pubmed.ncbi.nlm.nih.gov/23664836/

Antiparasitic Activity

Many naturally derived products used as antiparasitic remedies have much of their activity against parasites attributable to the presence of Quercetin and related compounds found together in the plant species which are used therapeutically. Such medicinal plants  have been used in the treatment of parasites since ancient times.

Antibacterial Activity

Quercetin has been shown to have strong action against many bacterial species, including Helicobacter pyloriYersinia enterocolitica, Pseudomonas aeruginosaEscherichia coliS. aureusP. fluorescens, and others.

 Antifungal Activity


Quercetin exhibits antifungal activity against various pathogenic fungi. It has been reported to inhibit the growth of Candida species, Cryptococcus neoformans, Aspergillus species, and others. Quercetin alters their cell membrane, leading to cell death. Quercetin has also been found to be synergistic with other antifungal medications, and so can be used as an adjunctive treatment for  fungal infections.

 Antiviral Activity

Quercetin has been shown in many studies to be active against a variety of viruses, and is synergistic with Vitamin C’s antiviral action.

In summary Quercetin is a very safe compound that can be incorporated into a person’s supplement regimen for a myriad of beneficial effects.

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