How Quercetin Works: Health Benefits of Quercetin

Quercetin is a flavonoid antioxidant found in plant foods. It is found in leafy vegetables, tomatoes, broccoli, and berries. Quercetin is actually a plant pigment. In the human diet, quercetin is one of the most abundant antioxidants. It destroys free radicals, and thus, fights against aging and inflammation. Some people get quercetin from their diet while some may need to take supplements. 

Quercetin has antiviral, antimicrobial, anti-allergic and anti-inflammatory properties. It can suppress inflammatory pathways and functions. It also shows strong effects on inflammation and immunity.

It offers protection against heart disease, cancer, and age-related diseases since it is a natural antioxidant and anti- inflammatory agent. Quercetin also gives color to flowers and fruits. It belongs to a group of polyphenolic flavonoid substances and is a naturally occurring flavonol compound. Usually, it is found in the Western diet. Rich dietary sources of quercetin are red wine and black tea.

How does quercetin work?

A number of inflammatory health problems such as heart diseases, allergies, infections, arthritis, chronic fatigue, and blood vessel problems can be managed by anti-inflammatory foods that contain quercetin. These foods are able to scavenge free radicals and slow down the process of aging.

Oxidative stress happens in people due to high-stress levels, poor diet, less sleep, and exposure to certain toxic chemicals. Quercetin lessens the oxidative stress and slows the aging progress. Through cell signaling pathways such as kinases and phosphatases, it regulates the response of the immune system to outside stress. Kinases and phosphatases are needed for proper cellular functions.

Quercetin is beneficial for the animals as well as humans. It intervenes in various preventive and therapeutic ways at the cellular level. The various ways in which it acts are:

• Inhibits or inactivates enzyme and pathways to prevent diseases from developing.
• It reduces cellular degradation.
• It promotes the production of molecules to maintain healthy cells.

Properties of Quercetin 

• Anti-inflammatory - The production of inflammatory proteins such as tumor necrosis factor alpha is inhibited by quercetin. Quercetin prevents inflammation in conditions such as cancer, nasal allergies, cardiac hypertrophy, and high cholesterol.

• Antihistamine - Quercetin prevents histamine release. Histamine which is an inflammatory substance that causes the symptoms of allergy. 

• Inhibiting Chemokinesis and Cytokines - Quercetin prevents the recruitment of mast cells. It also stabilizes the release of mast cells and blocks their degranulation. By doing this, histamine, serotonin, and proteases are not released. Hence, allergic symptoms are not caused. The recruitment, activation, and degranulation of mast cells are blocked by quercetin. Symptoms of allergic rhinitis can be prevented by quercetin by stabilizing the mast cells in an inactive state. Thus, it is known to have broad spectrum of actions. Quercetin downregulates the balance of Th1 and Th2 and avoids the activation of mastocytes. When early stages of an allergic reaction show its effect, quercetin reduces the response of Th2. Therefore, the production of IgE is inhibited and the masctocyte is inactivated.

• Antibacterial Activity - Quercetin is known to possess antibacterial properties against almost all strains of bacteria that cause respiratory, skin, gastrointestinal, and urinary tract disorders.

• Anticarcinogenic - The hyperactivation of protein kinase C is believed to play a role in tumor progression. Studies have shown that quercetin exhibits antitumor activities. However, its mechanism is not yet known. Studies have shown its anticarcinogenic effects by up-regulation of p53 and BAX in HepG2 cells and downregulation of PKC, PI3K, COX-2, and ROS.

• Causes Cell Death and Inhibits the Proliferation of Cancer Cells - In the cellular reproductive cycle, it helps stop the growth of cancer cells at some point.

• Antioxidant - Through antioxidant activities such as scavenging of free radicals, quercetin inhibits the oxidation of substances that lead to heart disease and skin cancer. Thus, it protects the cells. Quercetin also protects the body against reactive oxygen species. It acts as a second line of defense by scavenging free radicals. It inhibits the initiation of oxidation chain, prevent the propagation of the chain, and may terminate the chain by causing reaction between two radicals.

• Antiviral - Quercetin is known to inhibit the enzyme needed by the HIV virus to replicate. Hence, it is known to inhibit viral replication and improve the function of immune system. It also acts in multiple ways to bring out its antiviral effects. The ability of the virus to infect the cells is reduced. It inhibits the ability of viral cells to replicate and reproduce as well as reduce their resistance to pharmaceutical drugs. Quercetin blocks the activity of the virus at every level. Its systemic, multifaceted interference and powerful nutraceutical therapy can be useful for many conditions. Quercetin's antiviral effects have been studied in hepatic viruses, respiratory viruses, and HIV.

• Immune System Booster - Connective tissue molecules are required for protecting the cells from bacteria and other harmful substances. The enzyme hyaluronidase breaks down these molecules. Quercetin is known to inhibit the action of this enzyme, thereby protecting the cell and also stimulate the formation of immune cells.

• Decreases Leukocyte Immobilization - Oxygen-derived free radicals are formed due to immobilization and adhesion of leukocytes to the endothelial walls. Generally, the leukocytes move freely along the endothelial walls. However, in certain conditions such as inflammation and ischemia, many factors may cause their adhesion, thereby immobilizing them. Quercetin oral administration was known to reduce the number of immobilized leukocytes and protects against inflammatory conditions.

• Inhibits the Actions of Xanthine Oxidase - An important route in the oxidative injury is the xanthine oxidase pathway. Xanthine dehydrogenase and xanthine oxidase metabolize xanthine to uric acid. Xanthine dehydrogenase is changed to xanthine oxidase during oxidative stress. Quercetin decreases the oxidative injury by inhibiting xanthine oxidase activity.

• Scavenging Action - In reperfusion ischemic tissue damage, quercetin was known to exert a protective effect by scavenging the free radicals, which induce tissue injury. Quercetin prevents tissue injury by scavenging the free radicals and also inhibit LDL oxidation. It can also protect against atherosclerosis.

• Modulates Gene Expression - Quercetin reduces phosphorylation of BAD and activation of caspase 3, thereby induces inhibition of both Akt/PKB and ERK phosphorylation. One of the major factors that cause pathogenesis of chronic inflammatory diseases is TNF-alpha. It also triggers the release of cytokines, inflammatory mediators, and inflammatory mediators. Quercetin inhibits its release and gene expression. This showed that quercetin has the capacity to modulate the response of the immune system and has an anti-inflammatory activity. The inhibition of TNF-alpha production is an approach to treating several inflammatory diseases. TNF has an effect on differentiation, growth, and death of immune cells.

• Interaction with Other Enzymes - Calmodulin transports calcium ions across cell membranes. It also initiates cellular processes. It is a calcium regulatory protein. Quercetin acts as a calmodulin antagonist and functions at cell membrane level. Calmodulin-dependent enzymes present at cell membranes such as phospholipases and ATPases are inhibited by quercetin. Thus, membrane permeability is influenced. Other enzymes that control various cellular functions such as the release of histamine from mast cells are also inhibited by quercetin. Quercetin also inhibits the action of phospholipases, cyclooxygenase, and lipoxygenase. Hence, it is beneficial in maintaining the body's tissue and structure. The conversion of arachidonic acid is catalyzed by the enzymes cyclooxygenase and lipoxygenase. A key substrate for substances such as inflammatory prostaglandins, thromboxane, and leukotrienes is arachidonic acid. Phospholipases catalyze the release of arachidonic acid.

• Inhibitory Action of Inducible Nitric Oxide Synthase - By interfering with the inducible nitric oxide synthase activity, quercetin reduces ischemic reperfusion. Endothelial cells, macrophages, and several different types of cells produce nitric oxide. Early release of needed nitric oxide but in higher concentration can cause an oxidative damage. In such conditions, the production of both nitric oxide and superoxide anions is increased by activated macrophages. Nitric oxide produces peroxynitrite by reacting with free radicals, which is more damaging. Peroxynitrite oxidizes LDL and causes irreversible damage to the cell membrane. Quercetin destroys the free radicals so that they cannot react with nitric oxide, and thus, decreasing the damage. Sometimes, these nitric oxides are viewed as radicals by flavonoids and are scavenged by them.

Quercetin helps in the following ways:

Lowers Inflammation

As we age, the natural process of oxidation takes place, which causes the aging process. Quercetin fights the processes of oxidation. Free radicals damage the cell membrane, cause death of early cells, and increase cell mutations. Quercetin stops the free radicals from damaging our body. The root of diseases such as heart disease, certain mental disorders, autoimmune disorders, and cognitive decline is inflammation. Quercetin has anti-inflammatory properties. Its effects of fighting inflammation have been found in foods. It effectively fights against the following conditions:

• Heart disease
• Atherosclerosis
• Circulatory problems
• High cholesterol
• Eye-related problems
• Allergies
• Stomach ulcers
• Viral infections
• Cancer
• Inflammation of the bladder
• Prostate and ovarian disorders
• Hay fever
• Asthma

Keeps the Heart Healthy

People with heart problems benefit from quercetin since it can reduce inflammation and oxidative stress. Those who eat foods containing quercetin are at a lower risk of developing cardiovascular diseases. Studies have shown that quercetin lowers the risk of arteriosclerosis, which can cause heart attack or stroke. It also helps in regulating the level of blood pressure and protecting the body from LDL. Studies have found that people who eat foods containing quercetin have lower cholesterol levels and less chances of hypertension.

Maintains Healthy Skin

Mast cells trigger allergic reactions, autoimmune disorders, and inflammatory diseases. Quercetin is capable of blocking these cells. It also protects the skin form photosensitivity and dermatitis. When taken as a supplement, its antioxidant and anti-inflammatory compounds naturally help to fight allergic and inflammatory diseases.

Improves Endurance

Quercetin might increase the endurance and performance of athletes. It is known to have positive effects on the body. Querectin is known to increase the health of blood vessels. Due to intense training and exhaustion, the person becomes susceptible to illnesses. Studies have shown that quercetin boosts the function of the immune system by preventing susceptibility to diseases.

Fights Allergies

Histamine is released when the body detects an allergen. The immune system's reaction causes symptoms, which make the person uncomfortable. Quercetin's natural antihistamine and anti-inflammatory properties can help minimize asthma attacks, skin sensitivities, seasonal allergies, and foods allergies. Quercetin decreases allergic symptoms such as coughing, sneezing, runny nose, watery eyes, swollen lips or tongue, indigestion, and hives by stabilizing the histamine release from immune cells.

Fights Against Cancer

Studies have found a link between a diet rich in quercetin and a lower risk of cancer. Quercetin might have antiproliferative effects on cancerous cells due to its chemopreventive activity. Hence, quercetin becomes a natural therapy for treating cancer. It can fight against cancer by stopping certain processes such as the growth of tumors, cell mutation, and symptoms associated with radiation and chemotherapy.

Helps Relieve Pain

Quercetin helps relieve pain, which is associated with conditions such as arthritis, prostate problem, and infections of the respiratory tract. Studies have shown that quercetin supplements have reduced bladder pain in some people. Quercetin does this by reducing inflammatory pain.

Mechanism of Oral Supplements

Quercetin in drug form is a specific quinone reductase 2 inhibitor. Inhibition of QR2 in malarial parasite may cause lethal oxidative stress. Also, its antioxidant activity is very helpful in killing the malarial parasite.

Quercetin can cause various side effects such as headaches and tingling of extremities when quercetin is orally taken. If it is taken intravenously, it may cause sweating, vomiting, and nausea. An overdose of quercetin may cause kidney damage.

Pregnant women and breastfeeding mothers should avoid quercetin supplements. People with kidney disease should also avoid quercetin as well. Before taking quercetin, inform your doctor if you have taken or currently taking the following medications:

• Warfarin
• Clopidogrel
• Digoxin
• Corticosteroids
• Aspirin
• Cyclosporine
• Chemotherapy drugs
• Medications that affect liver function

Flavonoids like quercetin have shown to play an important role in preventing cancer of the breast, ovary, colon, lungs, and prostate.