Quercetin – what properties does it have and in which products can it be found?

Quercetin, found in varying amounts in fruit and vegetables, is the flavonoid most commonly consumed by humans. Although its antioxidant potential has long been recognised, other equally beneficial properties of this natural substance are also being investigated. What role does quercetin play in our diet, and what should we know about its potential health benefits and contraindications for its use?

Quercetin – what is it?

Polyphenols and the flavonoid subgroup form a very large structure of secondary plant substances. Currently, there are about 5,000 different representatives known. One of them is quercetin, which belongs to the flavonoid subgroup, i.e. yellow plant pigments, or more precisely, pentahydroxyflavonoids.

The scientific name for quercetin, ‘quercetin’, contains the word ‘quercus’, which means oak in Latin. The velvet oak (Quercus velutina) contains, among other things, the highest amounts of quercetin of all plant species known in the world. Although little known to most people, quercetin is the most common flavonoid found on our tables. Studies have shown its positive effect on general inflammation parameters, allergic reactions and blood pressure. This compound is also associated with the treatment of diabetes complications and anti-cancer properties.

Anti-inflammatory and antioxidant properties of quercetin

A number of clinical studies have found that quercetin acts on the human body on many different levels, often in very complex ways. On the one hand, it acts as an antioxidant and can therefore interrupt the chain reaction of free radicals that attack cells and lead to oxidative stress. It prevents cell damage and promotes cell longevity.

On the other hand, quercetin inhibits the release of histamine, which helps combat allergic and inflammatory reactions. Laboratory analyses also show that quercetin has anti-cancer and anti-cholesterol properties. Other positive aspects of quercetin include:

Quercetin has anti-inflammatory properties, antiviral properties, antioxidant properties and cardioprotective properties.

Quercetin – in which food sources can we find it?

As already mentioned, quercetin is the most abundant flavonoid in the modern diet. It is estimated that the average person consumes between 10 and 100 mg of quercetin per day from various food sources.

Quercetin is found in products such as:

• Apples

• Blueberries

• Grapes

• Onions

• Shallots

• Capers

• Tomatoes

• Honey

• Nuts

• Wine

• Teas

In short, if our diet contains a lot of unprocessed food, we will be able to successfully supply large amounts of quercetin. It has been shown that in Mediterranean countries, where the cuisine is characterised by a high content of fruit and vegetables, people consume significantly more quercetin. This fact may indicate, among other things, the health-promoting aspect of the Mediterranean diet.

The health-promoting role of quercetin in the human diet

Scientific research on the effects of quercetin on the human body has linked its antioxidant properties to various benefits that are potentially beneficial to our health. We distinguish the noticeable effects of quercetin when used daily, including:

• Reducing inflammation – although a small amount of inflammation is necessary for the body to respond properly to infections and diseases, prolonged inflammation is associated with many unpleasant consequences. Quercetin, with its anti-inflammatory properties, prevents this condition by reducing the discomfort associated with pain resulting from the body's inflammatory activity.

• Lowering blood pressure – quercetin can help lower blood pressure. It has a relaxing effect on blood vessels, improving systolic and diastolic blood pressure values in all study participants;

• Supporting physical performance – taking quercetin may improve the performance of people who participate in endurance sports. It promotes the regeneration of the body and prevents inflammation immediately after training;

• Controls blood sugar levels – the compound quercetin may have a potentially positive effect on lowering blood sugar levels. This protects the body from complications of diabetes;

• Helps fight ageing – quercetin can rejuvenate or eliminate ageing cells and reduce the effects of oxidative stress on newly formed cells. This effect is due to the antioxidant properties of the compound;

• Reduces the risk of neurological diseases – research suggests that the antioxidant properties of quercetin may help protect the brain from various neurological diseases, including Alzheimer's disease and dementia;

• Potential anti-cancer effect – quercetin has antioxidant properties – it may promote the body's anti-cancer response, precipitating the formation of cancer cells;

Quercetin for allergies – health properties

Can quercetin be an effective anti-allergic agent? Japanese studies have shown that quercetin is one of the few flavonoids that has anti-allergic properties. Scientists have discovered that the compound inhibits the secretion of histamine H1, whose markers are greatly enlarged in people with allergic rhinitis. It is therefore obvious that inhibiting the function of histamine H1 receptors may be associated with alleviating allergic symptoms.

Furthermore, thanks to the antihistamine effect of quercetin, the compound blocks enzymes involved in inflammation and suppresses pro-inflammatory chemicals such as histamine. Quercetin can successfully inhibit anaphylactic reactions associated with peanut consumption in mice, but it is unclear whether quercetin has the same effect in humans.

Quercetin for dogs – how does this dietary supplement support allergy treatment?

Can quercetin be an effective remedy for dogs? Quercetin for dogs is a natural anti-allergic medicine that can help alleviate allergy symptoms in animals. It promotes the treatment of hay fever and other allergic diseases. It can also help boost immunity and alleviate the symptoms of respiratory diseases in dogs.

Quercetin is also a safe and effective treatment. Before using quercetin in dogs, it is important to consult a vet. How to administer quercetin to dogs? It can be used as a dietary supplement in the form of tablets or capsules, or administered with food.

Quercetin for children – can it be supplemented?

Quercetin is present in a wide range of foods. It is therefore no surprise that children come into contact with it from an early age. However, is it safe? Quercetin given to children in food is considered safe for health. It has the same, albeit reduced, effect as that given in supplements.

Unfortunately, due to the lack of current scientific literature on the use of quercetin supplements in children, it is advisable to administer the compound in supplement form to children in a thoughtful and rational manner. The recommended daily dose for children should not exceed 500 mg.

Quercetin and the thyroid gland – is it safe?

In excessive doses, quercetin may cause undesirable side effects in thyroid function. However, quercetin should not be abandoned. Safe, recommended daily doses of quercetin have no direct effect on thyroid function. To counteract the potential effects of quercetin, it is worth considering supplementation with selenium and zinc, two ingredients that balance thyroid function and thyroid hormone levels.

Quercetin – potential side effects of dietary supplements

Consuming quercetin in foods such as fruits and vegetables does not cause side effects. In the form of a dietary supplement, quercetin appears to be equally safe when used in the specified daily dose.

High doses of quercetin may cause headaches or tingling in the hands and feet. Therefore, do not exceed the recommended daily dose. If you experience any side effects while taking quercetin supplements, contact your doctor.

Quercetin – are there any contraindications for its use?

Are there any contraindications associated with the use of quercetin? The compound is safe for pregnant and breastfeeding women when consumed with food. However, there is a lack of research on the safety of quercetin supplements for pregnant and breastfeeding women. As with any dietary supplement, consult your doctor before taking quercetin, as the compound may also interact adversely with certain groups of medications, including antibiotics and high blood pressure medications.

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