Quercetin: The ultimate anti-inflammatory plant compound

quercetin content

Last Updated December 20th, 2021

What is Quercetin?

Quercetin is a plant pigment that is found in various food items, including fruits and vegetables. It is more abundantly found in red and orange coloured plant products. It is a polyphenol compound and it has various anti-carcinogenic, anti-inflammatory and antiviral activities effects on the body.

It is one of the most abundantly available dietary anti-oxidants and helps the body to combat free radical related damage. Recent research has also suggested that quercetin can be useful in combating ailments like cardiovascular disease, cancer and neurodegenerative diseases. In addition, it can also promote a healthy heart and younger-looking skin with the right level of use.

Some of the most common foods that contain this compound are onions, apples, honey, citrus, tomatoes, kale, blueberries and sweet potatoes. It is also found in drinks like green tea and red wine.

Quercetin Content 

The preparation and storage of the food items are very important in determining the quantity of quercetin in them. It has been detected that boiling reduces quercetin levels due to thermal degradation. A similar result is obtained while frying food items.

The temperature and conditions of food storage also affect the levels. Onions were shown to lose their quercetin content by up to 33% within the first two weeks of storage. The conditions of growth of these plants are also another factor that determines the quercetin levels in the fruits and vegetables. Plants exposed to a higher level of UV-radiation are shown to have higher amounts of the compound.

This is a result of quercetin being a part of the defence mechanism of the plants against UV radiation. Previously, quercetin was classified as Vitamin P and not much details were known about it. Detailed studies in the 1990s led to the discovery of various benefits of this compound.

Properties of Bioflavonoids

While the name suggests that flavonoids have an important role to play in enhancing the taste of plant products, in reality it is not so. The flavonoids have a large family with more than eighty thousand members in it. As a bioflavonoid, Quercetin is found in many forms and all of them do not have the same properties. There are a few forms that are not readily absorbed by the body and can cause allergic reactions.

Some forms have a very short half-life and have no positive effects unless consumed with short time spans. It has been estimated that an average person consumes around 5 and 40 milligrams of the compound daily through various food sources. This depends on the food patterns of the particular region and in areas where there is high consumption of fruits or tea, daily intake of quercetin is higher.

The compound is also available as a dietary supplement in various forms. Quercetin is metabolized in various internal organs like the small intestine, colon, liver and kidney. It is then absorbed or excreted depending upon the requirements of the body. Apart from being antioxidants, flavonoids also acts as dyes and their presence in red wine and beetroots are a prime example of that.

In addition, they also work as natural insecticides and fungicides. They were also used in many traditional medicines to prevent haemorrhoids and subcutaneous haemorrhage. Flavonoids have a property that makes them prevent the oxidation of Vitamin C and help in its absorption the body. They also help in boosting the immune system and reduce the risk of a stroke. It is to be noted that even with all these benefits, the amount of free Quercetin in the plasma is very low.

Quercetin and free radicals

Free radicals are an unstable atoms, generated from various chemical reactions in the body that can cause immense damage to the human body. While seeking other atoms to pair with, these free radicals cause a lot of harm to the cells and the DNA.

They are being considered as a major cause behind various ailments like cancer, atherosclerosis, Alzheimer’s disease, Parkinson’s disease. The gradual effects of free radical induced damage can also lead to premature ageing. Quercetin can act as an efficient free radical scavenger, thereby reducing the damage of the various tissues.

This also prevents the free radicals from reacting with nitric oxide in the cells and reduce the chances of the formation of the highly damaging compound peroxynitrite.

The benefits of Quercetin

Quercetin is said to have multiple health benefits even though proper scientific evidence for the same is absent. The overall findings on the beneficial effects of quercetin have been encouraging but inconsistent in some ways. The following are the main benefits that make this compound special.

Anti-oxidant properties

Quercetin is highly effective in neutralizing the free radicals in the body. The free radicals increase the probability of disease and speed up the ageing process. The various factors that contribute to the growth of free radicals in the body are pollution, smoking, radiation, greenhouse gases and others. So the compound serves an anti-cancer function and it is shown to reduce the effects of pancreatic, prostate, colorectal and skin cancers. Further studies in this aspect are ongoing to determine the exact role of quercetin.

Anti-cancer properties

In general, research has indicated that a plant based diet based on fruits and vegetable can reduce a large percentage of cancers in the body. A study on mice have shown Quercetin exhibiting inhibitory effect on the growth of melanoma. Other studies have shown it having a negative effect on the growth of cancer cell sin various forms of cancer including breast, colon, prostate and lung cancers.


Inflammation is a common symptom that can be temporary or permanent depending on the cause. While some bacterial or viral infections can give rise to inflammations, it can also be caused by conditions like cancer, heart disease and rheumatoid arthritis. Quercetin is said to have the right properties to reduce inflammation which is linked to its anti-oxidant properties. So far, the research on human subjects has yielded mixed results. The compound reduced inflammations in healthy male athletes but it was ineffective on women with chronic rheumatoid arthritis.


allergSeasonal allergies pollenQuercetin is a natural antihistamine and it helps the immune system to get rid of allergens. The sneezing or coughing reactions are triggered by histamines in order to eliminate allergens from the body. This can cause health impacts at times, including a negative impact on the respiratory system. Quercetin can have a positive impact on the intracellular enzymes and reduce excessive histamine excretion. This can make it effective for the treatment of bronchitis and asthma. It acts as a bronchodilator and can reduce congestions in the air pathways.

Prevents infections

Quercetin is said to have antibacterial properties which makes it an effective agent in combating various infections. These include infections in the stomach, lungs and the urinary tract. It can also assist the body to combat various viruses like adenovirus, herpes simplex virus, the Japanese encephalitis virus, etc. It also exhibits antibacterial properties against various bacteria causing respiratory, gastrointestinal, skin and urinary disorders.

Promotes healthy skin

The properties in Quercetin can help in promoting a healthy and youthful skin. Being an antioxidant, it prevents premature ageing of the skin and also helps in enhancing the complexion. The compound is making its way into various skin-enhancing products due to these properties.

Prevention of heart diseases

Quercetin improves blood flow and helps to maintain a healthy level of blood pressure. Its antioxidant action prevents the oxidation of LDL cholesterol which is harmful to the body. Oxidation causes these cholesterols to stick to the walls of the artery which in the long run can result in atherosclerosis, heart attacks and strokes. As per research data, individuals consuming 150 milligrams of quercetin per day had reduced systolic blood pressure as well as lower cholesterol levels.

Prevention of neurological diseases

Even though research is still ongoing, it has been shown that quercetin is effective against diseases like Alzheimer’s and Parkinson’s. Oxidative stress is a major cause of these diseases and it is promoted by the imbalance of free radicals. The antioxidant properties of the compound help in keeping the free radical levels under control. In some cases, specific metals can have an adverse effect on the nervous system and quercetin is believed to have the capability to improve that condition.

Enzyme system activity

Quercetin interacts with various enzymes like calmodulin, cyclooxygenase and Lipooxygenase. It stabilizes the cell membranes and also reduce the secretion of histamine from mast cells. The enzyme inhibitory action of Quercetin has multiple benefits in the cellular level and it results in more comfort in the various body tissues

Stress prevention

The high-stress levels can produce cortisol, which, in the long run, can be very harmful to the system. Cortisol can result in the breakdown of protein cells in the body and lead to the damage of muscle cells. Quercetin can fight the negative effects of stress as it suppresses the enzymes that control the release of cortisol.

Athletic endurance

Quercetin is said to have a positive impact on athletic performance and pain reduction. While animal studies in this aspect have shown positive results, studies on human subjects have not yielded positive results. The research data indicates that short-term supplementation with quercetin have no significant changes in muscle performance. Some researchers claim that the role of quercetin in enhancing athletic performance can be nothing but a placebo.

Side effects of Quercetin

While having various beneficial functions, quercetin have some minor side effects. Being a naturally occurring compound, it does not have any major downsides.

Consuming more than 1,000 mg of quercetin in a day can lead to headaches, tingling of arms and legs and stomach aches. Kidney damage can happen in some extreme situations and the compound can aggravate kidney problems. The right step will be to exercise caution while consuming quercetin supplements in case you have a kidney related problem.

For pregnant or nursing women, it is best to consult the doctor before consuming any quercetin supplements as there are very few studies conducted on this aspect. Quercetin can also interfere with some drugs including antibiotics and if you are consuming any such drugs, you should seek medical advice before supplementation.

Some studies have found Quercetin effecting metabolism in human liver cells in a way that it increases the estradiol level and reduces the level of other forms of estrogens. Since grapefruit contains high amount of Quercetin, many patients taking oral estradiol are advised to avoid the fruit.

Quercetin levels in various food items

Food Quercetin Content (mg/100gm)
Raw Broccoli2.8
Raw carrots0.4
Raw cranberries2.8

The right dose of Quercetin

The right dose of quercetin depends on the age, sex and overall health condition of the individual. There is no specific research at this stage that points out the best possible dose of quercetin. Keep in mind that quercetin can be obtained naturally from a wide variety of food items and drinks like tea and wine. At present, there is no data on the effects of prolonged supplementation of quercetin so the risks are unknown.

Some studies have indicated the orally introduced doses of Quercetin are unlikely to cause any damages to the system, but no dose levels were mentioned. So it is not possible for dieticians to recommend a healthy dose of quercetin supplements apart from following a wholesome and healthy diet.

Make sure that you consult a healthcare professional before consuming additional quercetin and follow the manufacturer’s instructions provided for every supplement.

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