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Quercetin: A Review of its Health Benefits

June 1, 2012

Quercetin is categorized is a type of flavonol. Flavonols are present in a wide variety of fruits, vegetables, plants, herbs & spices. Azadirachta indica (Neem) and Camellia sinensis (Green tea) are good sources of quercetin. In a extensive review by Kelly (Volume 16, Number 2 Alternative Medicine Review, 2011) he evaluates the science behind some of Quercetin’s health benefits.

Antioxidant

An extensive amount of research has focused on the antioxidant potential of quercetin. The evidence suggests quercetin’s antioxidant effects give protection to  the brain, heart, amongst other tissues against ischemia reperfusion injury and other toxic agents that can induce oxidative stress. In two studies of overweight and obese subjects with metabolic syndrome traits, a daily dose of quercetin for six weeks decreased plasma concentrations of atherogenic oxidized Low Density Lipids.

 

Inflammation, Injury, and Pain: quercetin has been shown to inhibit production of inflammatory enzymes (cyclooxygenase [COX] and lipoxygenase [LOX]).

Arthritis: Although quercetin by itself does not appear to be beneficial in rheumatoid arthritis, when combined with other nutrients it looks like it can reduce some of its symptoms.

Allergy, Asthma, and Atopic Disease

Studies on quercetin suggest an anti- allergy effect. Evidence indicates that quercetin might have therapeutic potential for allergic airway disease. Several studies conducted in animal model systems have reported that quercetin, provided orally or administered via inhalation, has anti-asthmatic activity.

Cancer

There is a plethora of evidence from model studies quercetin’s anti-cancer benefits. The results suggest a range of anticancer mechanisms, including antioxidant, antiproliferative, pro-apoptotic, cell signaling effects, and growth factor suppression. In summary, evidence suggests that quercetin is a good candidate for further anticancer clinical studies.

Cardiovascular Disease

Quercetin appears to ameliorate cardiac hypertrophy induced by pressure overload in an animal model.

Additionally, quercetin inhibits platelet aggregation and thrombus formation in a study on humans. In other studies it appears to be effective in improving blood pressure and may help with modulating cholesterol levels in humans.

Gastroprotective and Oral Mucosa Effects

A protective effect of quercetin against gastric ulcers has also been reported. It also appears that Quercetin weakly inhibits the growth of Helicobacter pylori.

Hypertension

A range of scientific have consistently demonstrated a blood pressure (BP) lowering effect with administered Quercetin. Quercetin induces a progressive, dose-dependent, and sustained reduction in BP in a variety of model systems of hypertension and metabolic syndrome.

In Humans evidence indicated that Quercetin may effect the nitric oxide status of endothelial tissue and and improve the hypertensive state.

Immunity and Infections

Quercetin has shown antiviral activity against reverse transcriptase of retroviruses like HIV, Herpes simplex virus type 1, polio-virus type 1, parainfluenza and various other viruses and bacteria.

 

Metabolic Syndrome Traits and Obesity

Quercetin supplementation decreased blood pressure slightly in overweight and obese subjects with metabolic syndrome. Quercetin also decreased HDL and increased the LDL:HDL cholesterol ratios in studies. Overall there seems to be a varied range of success when Quercetin was administered for Metabolic syndrom and Obesity.

Mood Disorders

Quercetin has shown anti-anxiety and antidepressant effects in model systems. It appears that quercetin can inhibit monoamine oxidase and can decrease stress-induced brain corticotropin-releas- ing factor (CRF) which has been implicated in anxiety and depression. It may explain some of the relaxing activity of Green Tea.

 

Sleep

Quercetin significantly increased non-rapid eye movement (non-REM) during dark periods in an animal model and significantly decreased REM sleep. This impact on sleep was probably due to quercetin-induced activation of GABA(A) receptors.

Synergistic Effects

Quercetin might also influence the bioavailability of some dietary supplements. It appears to improve the bioavailability of epigallocatechin gallate (ECGC) found in Green Tea. Initial results suggests that quercetin might have synergistic effects with some drugs too. For example Quercetin can reverse the development of morphine tolerance and dependence in an animal model system.

With respect to Cancer, quercetin might have synergistic interactions with some chemo-therapies and could play a role in multi-drug resistance.

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