Quercetin is a plant flavonol from flavonoid group of polyphenols which is mostly found in vegetables, fruits, grains and leaves. Kale and red onions contains high content of quercetin. It is used as an ingredient in beverages and dietary supplements. It is considered to be most abundant antioxidants in human diet and plays a crucial role in counteracting free radical damage, effects of aging or inflammation. Quercetin glycosides and other flavonoids such as myricetin and kaempferol acts as anti-microbial, anti-viral, anti-allergic and anti-inflammatory agents with an ability to positively express in various cell types in both humans and animals. Quercetin is a flavonoid which forms chemical backbone for other flavonoids such as naringin, hesperidin, tangeritin and rutin. It is found bound to one or two glucose molecules (diglycoside and monoglycoside forms).
Food Sources of Quercetin
| Food name | Weight (g) | Quercetin (mg) |
| Capers | 100 | 233.84 |
| Lovage | 100 | 170 |
| Elderberry juice | 100 | 108.16 |
| Dock | 100 | 86.2 |
| Radish leaves | 100 | 70.37 |
| Wild rocket | 100 | 66.19 |
| Dill weed | 100 | 55.15 |
| Cilantro | 100 | 52.9 |
| Banana peppers | 100 | 50.63 |
| Fennel leaves | 100 | 48.8 |
| Juniper berries | 100 | 46.61 |
| Mexican oregano | 100 | 42 |
| Yellow onion | 100 | 41.9 |
| Red onions | 100 | 39.21 |
| Carob flour | 100 | 38.78 |
| Radicchio | 100 | 31.51 |
| Red leaf lettuce | 100 | 30.6 |
| Watercress | 100 | 29.99 |
| Hartwort leaves | 100 | 29.3 |
| Asparagus | 100 | 23.6 |
Health benefits of Quercetin
Quercetin is a plant pigment which occurs in various ethnic plants especially tea and onion, sufficient amount should be consumed regularly. It is important in terms of ethnopharmacology, it is used as anticancer, antioxidant and neuroprotective.
- Acts as an antioxidant
Flavonoids have antioxidant properties which help to neutralize free radicals by granting hydrogen atoms to it. It is observed that difficulty stimulated on correlating structure of flavonoids and its accountability for scavenging radicals. Formation of reactive oxygen species which reports diabetes, hypertension, atherosclerosis, heart failure and ischemic heart disease. It acts as antioxidant by preventing oxidative stress which is the major cause for generation of ROS. It is able to scavenge free radicals and bind transition metal ions.
- Prevent neurodegenerative diseases
Quercetin is a neuroprotective and neurotoxic. It is reported to be neuroprotector in rat brain when used with fish oil, it is beneficial for neurodegenerative diseases. It is reported to have low 6-hydroxydopamine induced oxidative stress in neurons of brain striatum of rats. Other study shows that quercetin treatment affects activity of nervous system by lowering intracellular glutathione contents.
- Antiviral properties
Quercetin is found to be effective against viruses such as parainfluenza type 3, herpes simplex type I, Sindbis, pseudorabies and respiratory syncytial. Quercetin has antiviral activity as it is capable to bind to viral coat protein and polymerases and also to damage DNA. Quercetin contains carcinogenic, mutagenic and anti-carcinogenic activity which is related to its ability of imposing or preventing DNA damage.
- Cancer prevention
Quercetin as well as other flavonoids derived from vegetables and fruits are crucial compounds that help to prevent cancer. Study have evaluated anti-carcinogenic effect on cell cultures which founds that slow growth of cancer cells was effected and assist to prevent apoptosis. Animal studies show that quercetin helps to protect certain types of cancer such as colon cancer.
- Canker sores
Canker sores are small and shallow lesions which occur in soft tissues of mouth or at base of gums. Quercetin helps to lower occurrence of mouth sores and promote mild symptomatic relief.
- Cardiovascular health
Heart diseases are the primary and leading cause of mortality in developed countries. The exact cause and mechanism involved in occurrence of heart disease is still a question, inflammation and oxidative stress has a crucial role. Quercetin is used as a safe alternative to anti-inflammatory and antioxidant drugs used for health conditions such as cardiovascular disease. Study shows that quercetin positively lowers several risk factors associated with heart disease such as blood pressure and also cytokine induced C reactive protein expression. It also acts as strong vasodilator agent.
- Lower inflammation
Inflammation is the normal biological process in response to microbial infection, injuries, chemical irritation and intoxication. Generally, inflammation is triggered by migration of immune cells from blood vessels to infected and injured area and discharge of mediators in order to combat injury or infection. It is also known for its anti-inflammatory properties. Study shows that rats when treated with quercetin combined with polysorbate, it resulted in edema inhibition in paw of rats. Applying quercetin glycoside through skin surface is found to be ineffective against inflammation due to its low value of absorption. Formulation of quercetin pentamethyleter is highly absorbed through skin route in rat and is effective against inflammation proving it to be strong anti-inflammatory.
- Cure for asthma
Asthma is a chronic lung disease which swells or narrows airways by causing difficulty in breathing. It helps to ease asthma symptoms. It helps to lower number and activation of inflammatory immune cells, cuts off level of histamine and ease airway smooth muscle. It is reported that at minimum concentration, quercetin is found to be effective against asthma maintenance medications and steroid inhalers which lowers resistance to air flow. It helps to lower pathologies of asthma such as neurotrophil and eosinophil enrollment, mucus and collagen production, bronchial epithelial cell activation and airway hyperactivity. Clinical study has shown that quercetin application helps to prevent and treat asthma in patients.
- Increase stamina
Daily intake of quercetin improves overall health and also enhances stamina. Experts recommend this flavonoid to enhance stamina to athletes. It is nutritional being extracted from natural fruits and vegetables. If one is trying to increase stamina naturally, start to take quercetin in form of vegetables and fruits.
- Relieves stress
Stressed body damages the body. The hormone known as cortisol is produced during this condition. It damages muscle tissue which leads to protein malfunctioning. It is able to combat these health problems. Intake of quercetin helps to suppress enzyme that controls cortisol in the body.
Recommended dosage
The recommendations of dosage could vary on health condition. It is estimated that typically most people get between 5 and 40 milligrams of it a day from common plant foods. According to some reports when stick to nutrient dense diet, one is likely to take in much more as much as 500 milligrams regularly. The estimated dietary intake is 25 to 50 mg regularly.
Precautions
It may cause side effects such as upset stomach and headache. Evidence has shown that byproduct could result to loss of protein function. Quercetin in very high doses could cause damage in kidneys. People with kidney problems, breastfeeding women and pregnant women should avoid quercetin. Quercetin supplements could interact with effectiveness of antibiotics, blood thinner medications and chemotherapy.
References:
https://en.wikipedia.org/wiki/Quercetin
http://www.naturalwellbeing.com/learning-center/quercetin/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5214562/
http://www.bioline.org.br/pdf?pr14215
http://pennstatehershey.adam.com/content.aspx?productId=107&pid=33&gid=000322
https://pdfs.semanticscholar.org/78e4/76120ff9ce073900329b36860213a7c3239b.pdf
https://www.naturalfoodseries.com/11-proven-benefits-quercetin/