Quercetin (3,4,5,7-pentahydroxylflavone) belongs to a class of water-soluble plant coloring substances called bioflavonoids. It is found in many often-consumed foods, including especially red onions, apple, tea, berries, and brassica vegetables, as well as many seeds, flowers, barks, and leaves. It is also found in medicinal botanicals, including Hypericum perforatum, Ginkgo biloba, Sambucus canadensis, and many others, and is usually a component of the therapeutic activity of the plant.

Quercetin Antiviral Activity

Studies indicate that quercetin may improve immune function and inhibit viral replication. Quercetin’s antiviral effect may be related to its ability to bind viral protein coat and to interfere with viral nucleic acid synthesis. Italian investigators demonstrated that they could use a quercetin-rich extract to up-regulate the antiviral immune response in cells infected with herpes viruses. Quercetin may exert antiviral effect against different types of viruses including herpes simplex virus type, polio virus type 1, reverse transcriptase of  HIV and other retroviruses. Quercetin exerts antiviral activity against reverse transcriptase of  HIV and other retroviruses, and was shown to lessen the infectivity and cellular replication of  herpes simplex virus type 1, polio-virus type, parainfluenza virus type 3, and RSV (respiratory syncytial virus). In an study, quercetin inhibited hepatitis C virus replication. Another study demonstrated that quercetin and quercetrin both have an inhibitory activity on the HIV reverse transcriptase and on casein kinase 2, an enzyme responsible for the transcription of several hiv genes. Quercetin has a triple action to fight viruses; 1- Reduces the ability of a virus to infect cells. 2- Inhibiting the ability of infected cells to replicate and reproduce. 3-Reducing resistance of infected cells to medication treatment.

Influenza viruses are major pathogens that cause respiratory infections in humans and animals. Findings from cell culture experiments provide potent evidence that quercetin may be efficacious as an anti-infective agent, reducing the  infectivity and replication of a variety of respiratory viruses.A new research demonstrated that quercetin and isoquercetin (a glucoside form of quercetin), substantially reduced the replication of influenza viruses in vitro and in vivo. In one study, quercetin inhibited influenza A virus replication in the lab more effectively than the anti-flu medication Tamiflu.

Quercetin, has been reported to inhibit infectivity and replication of a broad spectrum of viruses and may offset the increase in susceptibility to infection associated with stressful exercise. A study demonstrated that quercetin could decrease flu when animals were intentionally exposed. In this study mice were exposed to the flu virus under various conditions, including increased stress from exercise. The mice given quercetin offset the unfavorable effects of stress and demonstrated much less susceptibility to the flu. This study builds on an earlier human study where quercetin reduced ailment and maintained mental performance in physically stressed people. Trained cyclists consumed 1000 mg per day of quercetin (also vitamin C and niacin) for 5 weeks. After 3 weeks, subjects rode a bicycle three hours per day for 3 days to the point of exhaustion. After the exercise period,  45% of the placebo-consuming cyclists became ill, while just 5% of the quercetin group suffered any illness.

In another animal study found that quercetin inhibits both influenza A and B viruses, and viruses were not able to develop resistance to quercetin cure. When quercetin was used with anti-viral medications the anti-viral activity was even stronger, and the quercetin prevented the development of resistance to the medications that otherwise occurs. In studies with flu-infected mice, quercetin’s antioxidant effects were shown to play a role. Quercetin doses of 1-mg/day substantially decreased production of harmful superoxide free radicals by a type of white blood cell in the lung.

Rhinovirus, which is responsible for the majority of common colds, moreover causes exacerbations in people with asthma and chronic obstructive pulmonary disease. According to a research presented at the American Thoracic Society 2010 International Conference held, quercetin could be a cure for rhinovirus (RV)-caused infections. Hepatitis C is an important cause of  liver failure and liver cancers. In Aug 2009 cell study demonstrated that quercetin interfered with the gene signals that enable hepatitis C virus production. The researchers showed  that the Quercetin inhibits hepatitis C viral production in tissue culture, at least partially through its inhibition of heat shock protein expression. Therapy with quercetin reduced the infectious particle production to nontoxic concentrations of HCV.

Allergies and asthma are inflammatory conditions generally triggered by air or food-borne pollens and chemicals called “allergens.” Quercetin stops allergies in their tracks via 2 routes. 1)  It is a strong anti-inflammatory, keeping the lungs, nasal passages, and eyes from swelling as they normally do when allergens like pollen come into contact with the body. 2) Quercetin is a powerful antihistamine that prevents the release of itchy chemicals that make nose run and eyes water.

Quercetin Allergy Research

Allergic reactions occur when some foreign protein enters the bloodstream and triggers the release of  histamine and serotonin, which cause coughing, breathing difficulties, clogged sinuses, skin eruptions. Quercetin stabilizes the walls of the cells that contain histamine and serotonin and prevents the release of these chemicals. Quercetin is an powerful inhibitor of histamine release, which is the primary cause of allergic reactions and symptoms. Particularly it inhibits the manufacture and release of  histamine and other allergic and inflammatory mediators from mast cells and basophils. Test tube studies found that quercetin avoids immune cells from releasing histamine, and may thus help to lessen allergy symptoms such as runny nose, watery eyes, hives and swelling of the face and lips. Researches have shown an improved lung function and lower risk of some respiratory diseases (asthma and bronchitis) for individuals with high quercetin intake. When taken in combination with Vitamin C, quercetin acts as a natural antihistamine that reduces or eliminates allergic reactions.

An animal study in 2007 demonstrates that quercetin may help treat allergies. Reported in “Inflammation Research“, the study found that mice placed on a quercetin-enriched diet had a lessen in inflammatory chemicals linked to allergic conditions. Investigators in both Korea and Brazil protected animals from fatal allergic reactions to common food allergens by pre-treating them with quercetin in oral or inhaled forms. A Japanese study of 20 participant with pollen allergies found that quercetin reduced eye irritation and itching. The participants were given 200 mg of a specific form of quercetin for 8 weeks.

Quercetin’s ability to prevent allergic effects has significant effects for the prevention and cure of  bronchitis and asthma. Various researches have shown that animals pre-treated with quercetin or related compounds have significantly reduced reactions to chemicals that trigger asthma attacks. Experimental and anecdotal findings demonstrate that quercetin is more powerful as an anti-allergen when administered with the supplement bromelain. Vitamin C has also been shown to work synergistically with quercetin to lessen the severity of allergic reactions. The vitamin C, bromelain and quercetin and may help alleviate allergy symptoms, according to Dr. Kathi Kemper from the Baptist Medical Center.

Quercetin (3,4,5,7-pentahydroxylflavone) is a common chemical pigment in the rinds and barks of a wide variety of plants. It is found in many plants and foods, such as red wine, apples, onions, green tea,  berries, St. John’s wort, ginkgo biloba. Animal-based and test tube studies suggest that flavonoids do have anti cancer effects. Quercetin and other flavonoids have been shown in studies to inhibit the growth of cancer cells from prostate, colon, breast, lung, ovarian, and endometrial, tumors.

Quercetin Cancer Prevention and Treatment

Epidemiological studies suggest elevated quercetin consumption is associated with reduced risk of  various types of cancer. In vitro studies shown that the way quercetin inhibits cancer cell proliferation is by causing cell death and/or stopping the cells from growing at some point in the cellular reproductive cycle. In a animal study looked at the effect of quercetin on mice bearing abdominal tumors derived from a human pharyngeal squamous cell carcinoma line. The mice were given a daily intraperitoneal injection of quercetin. All doses analyzed (20-, 200-, 400- 800 mg/kg) showed significant inhibition of  tumor growth. The 20 mg/kg dose had an effect only slightly less than that seen with 800 mg/kg.  The researchers concluded that quercetin appears to be a selective inhibitor of tumor cell growth.

An early Phase I clinical trial of quercetin in patients with different cancer types showed a diminution in activity of enzymes required for tumor growth in nine of eleven patients studied. In a study reported in Carcinogenesis in 1991 found that quercetin reduced the incidence of colonic neoplasia in rodent models of mutagen-induced colon cancer. One clinical trial of individuals with a potent inherited tendency to develop colorectal cancer found that the combination of curcumin and quercetin  reduction the number and size of precancerous rectal tumors. Cleveland Clinic oncologists investigated quercetin in patients who had familial adenomatous polyposis. They combined the quercetin with curcumin, in 5 patients, treating and following them for 6 months. All patients had a diminution in both size (60%) and number of polyps (51%) over the course of therapy.

A 2005 study in the  Drug Metabolism and Disposition found that quercetin, halts the growth and induces apoptosis, of lung tumor cells in lab settings. The June, 2009 edition of  the Journal of  Experimental and Clinical Cancer Research demonstrated that quercetin is found to be protecting against the formation of  liver cancer cells, mainly due to its role as an antioxidant. In a article reported in Nutrition and Cancer in 2011, scientists found that quercetin blocks the ability of a carcinogenic chemical to induce cancerous changes in the liver cells of lab animals. Co-ingestion of quercetin with other flavonoids such as catechins can increase quercetin bioactive effects. Investigators from Rutgers University have reported the result of a study in the journal “Food and Function” that explains a synergistic relationship when green tea and quercetin are provided through. The study found that combining catechins with quercetin increased the cellular adsorption of  Epigallocatechin Gallate (EGCG) 2 times in kidney cancer cells and 4 times in lung cancer cells significantly increasing the effectiveness of this cancer fighting compound in vivo.

Quercetin has been shown to enhance the medicinal efficacy of cisplatin both in vivo and in vitro. In mice bearing human tumor xenografts, intraperitoneal therapy with a combination of 20 mg/kg quercetin and 3 mg/ kg cisplatin led to a significantly reduced tumor growth compared to therapy with either medication. An in vitro study demonstrated quercetin works synergistically with busulfan against human leukemia cell lines. Quercetin has been found to stop the angiogenesis of  the breast cancer cells, in those which have been resistant to medication tamoxifen, according to a research reported in Nov 2010 edition of  Food and Chemical Toxicity. Also, Quercetin has been shown in vitro to increase the cytotoxic effect of cyclophosphamide, and to lessen resistance to topotecan and gemcitabine.

Sulforaphane is a constituent of cruciferous vegetables such as broccoli cauliflower, cabbage and kale.  The isothiocyanate sulforaphane is abundant in broccoli sprouts in the form of  its glucosinolate  precursor. However the amount present varies widely among varieties of broccoli. A group of researchers at the “Johns Hopkins University School of Medicine” have shown that three-day-old broccoli sprouts contain 20 to 50 times the amount of chemoprotective compounds found in mature broccoli heads. Sulforaphane has been shown in vitro studies to have anticancer activities against breast, prostate, and urinary cancers. In preclinical studies sulforaphane has exhibited antineoplastic activities in multiple tumor models.

Sulforaphane Cancer Prevention and Cure

A preventive property of brassicas against cancer may be plausible due to their relatively high content  of glucosinolates. The cohort studies demonstrated inverse associations between the consumption of  brassicas and risk of stomach cancer, lung cancer, all cancers taken together. Of the case-control studies 64% demonstrated an inverse association between consumption of one or more brassica vegetables and risk of cancer at various sites. This association appears to be most consistent forstomach, lung, rectal and colon cancer, and least consistent for prostate, endometrium and ovarian cancer. Sulforaphane, one of naturally occurring isothiocyanates, has huge cancer chemopreventive potential. It modulates cell death, cell cycle, angiogenesis, susceptibility to carcinogens, invasion and metastasis and possesses antioxidant effects. In-vitro and animals-based studies have confirmed the anti-cancer properties and have showed  that the phytochemical decreases the frequency, size, and number of tumors.

Numerous in vitro studies in human colon, pancreatic, leukemia, lung, and skin cancer cell lines have showed sulforaphane’s inhibitory properties on cell cycle arrest, and research in  human bladder and prostate cell lines has shown it increases apoptosis. Sulforaphane provided important preservation against oxidative damage to prostate cells according to a study on prostate cancer reported in the 2009 Prostate. A study in the journal “Clinical Cancer Research” demonstrated that sulforaphane is able to kill breast cancer stem cells in mice and in laboratory cultures, and furthermore prevented new tumor cells from growing. In mice with experimentally induced prostate cancer, 6 µmol sulforaphane by oral gavage 3 times weekly from age 6 weeks onward decreased pulmonary metastasis incidence by 50 % and multiplicity by 63%.  The scientists believe a chemical called sulforaphane works with cells which lack an anti-tumour gene to fight prostate cancer. The gene, called PTEN, can allow the spread of prostate cancer if it becomes defective. In a study sulforaphane helped the gene to survive and help to fight the cancer. “PTEN is a tumour suppressor gene, the deletion or inactivation of which can initiate prostate carcinogenesis, and enhance the probability of cancer progression. We’ve shown here that sulforaphane has different effects depending on whether the PTEN gene is present”. Says Professor Richard Mithen.

A study from “Baylor College of Medicine” scientists shows a compound (sulforaphane) found in cruciferous veggies, is able to kill leukemia cells in the lab. The results reported in the journal “PLoS ONE“, demonstrated that incubating the compound, called sulforaphane, with cells of acute lymphoblastic leukemia caused the cancer cells to die.  Sulforaphane could help avoid or treat breast cancer by targeting cancer stem cells according to a study from scientists at the “University of  Michigan Comprehensive Cancer Center“. In the current study, investigators took mice with breast cancer and injected varying concentrations of sulforaphane. Investigators then used different established methods to assess the number of cancer stem cells in the tumors. These measures demonstrated a marked reduction in the cancer stem cell population after cure with sulforaphane, with little effect on the normal cells. Also, cancer cells from mice treated with sulforaphane were unable to generate new tumors. “This research suggests a potential new treatment that could be combined with other compounds to target breast cancer stem cells; says Max S. Wicha, M.D director of the U-M Comprehensive Cancer Center.

Scientists at the” Institute of  Food Research” believe that sulforaphane can boost the body’s own anti-cancer weapons.’ Sulforaphane is very important,‘ says Dr Maria Traka.‘The findings suggests that it helps maintain a healthy balance of antioxidants in the body to counter the effects of dietary, environmental, or other carcinogens. It is thought sulforaphane turns on genes that boost antioxidant levels and blocks a family of enzymes called HDAC that avoids the body from suppressing tumours. Histone deacetylases (HDACs) inhibitors, such as sulforaphane, can help restore proper balance and prevent the development of cancer. In a pilot study involving three healthy participants, a single daily dose of 68 g BroccoSprouts® (about 105 mg sulforaphane) significantly inhibited HDAC activity in  peripheral blood mononuclear cell cultures 3 and 6 hours following consumption, suggesting sulforaphane may induce cell cycle arrest and apoptosis in humans.