Quercetin: what it is, properties and benefits, rich foods, contraindications

You may have heard of it before, but what is quercetin? This element of vegetable origin has strong antioxidant and anti-inflammatory properties, which make it an excellent ally for your health. It is not uncommon to find it in the formulations of antiaging or neuroprotective food supplements.

But what are the properties of quercitin? And what benefits can you get?

There are some foods that naturally contain good amounts of quercitin. Introducing them into your diet could benefit your body. But what is the recommended dosage of quercitin? What are the risks of overeating?

Read on to learn more.

What is Quercitin?

Quercitin, or quercetin, is a molecule of plant origin, which belongs to the group of flavonoids. To be more precise, it is a flavonol. Like many flavonoids it has numerous beneficial properties, among which the antioxidant and anti-inflammatory power stand out. But why is it called that?

Its name “quercitina” already suggests its origin. Plants of the genus Quercus (various types of oaks) have good quantities of it. Even if they are not alone! Among the plant organisms there are numerous species for food use, which are an excellent source of quercitin.

The plant produces quercitin and other polyphenols with the aim of protecting itself, promoting growth (it is linked to the metabolism of auxin) and the process of chlorophyll photosynthesis. Without knowing it, however, some plants create molecules that are also very useful for human metabolism.

Quercitin chemistry

Let’s get into the details of chemistry. This molecule is produced (synthesized) by plants according to a series of metabolic processes involving numerous enzymes.

The metabolic pathway originates with a well-known amino acid: phenylalanine. This undergoes numerous modifications, to conclude the process with the action of flavonol synthase, the final enzyme, which gives rise to quercitin.

Before going to analyze which and how many are the advantages that quercitin brings to human metabolism, let’s understand well what molecule it is.

Polyphenols, flavonols, or flavonoids? There is often some confusion. Where does quercitin fit in?

We have already described these classes of phytocompounds in other articles, but let’s make a small summary:

  • Polyphenols are a large group, encompassing flavonoids, phenolic acids, stilbenes, and lignans.
  • Among the flavonoids (which are polyphenols) we find isoflavones (such as those of soy), flavones, flavonols, anthocyanins, flavonols and flavanones.
  • Quercitin is a flavonol, therefore a flavonoid of the polyphenol group.

Properties and benefits of quercetin

This flavonol has been extensively studied and its properties are now known and documented in science. Due to its antioxidant and anti-inflammatory role, it is used in the prevention of inflammatory diseases.

It can bring benefits to the circulatory, respiratory and nervous systems. And it is even used in a clinical setting, in oncological prevention.

Antioxidant action

This is the most described and studied property of our flavonoid. In fact, quercetin is one of our body’s most powerful allies in protecting us from reactive oxygen and nitrogen species: ROS and RNS (free radicals). These compounds are the main cause of cellular aging and oxidative damage.

However, our body has developed well-articulated defense systems that include “scavenger” molecules (the “scavengers” of free radicals) and antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx).

Quercitin, as well as vitamin C and vitamin A, plays the role of “scavenger” of free radicals. Furthermore, it keeps the enzymes used for the elimination of radicals active (reduced). That is, it acts on two fronts. That is why it is a powerful antioxidant that protects tissues from cell damage with good efficacy.

Powerful anti-inflammatory

Besides being a good antioxidant, quercitin plays a great role in reducing inflammation in the tissues. How does it work?

Some molecules, including free radicals, have the ability to stimulate our immune system, attracting pro-inflammatory molecules. It is a defense mechanism that our body implements against foreign bodies, but which can be harmful to itself at the same time.

Among these molecules, the main mediator of inflammation is TNF-α (tumor necrosis factor alpha). It is one of the main pro-inflammatory cytokines involved in the pathogenesis of chronic inflammatory diseases and is modulated by oxidative stress.

Quercitin acts by significantly inhibiting the expression of TNF-α, modulating the anti-inflammatory activity (stimulates anti-inflammatory cytokines and inhibits the activation of the pro-inflammatory factor NF-κβ). Also, let’s not forget its direct action in curbing oxidative damage!

Quercetin: benefits for the cardiovascular system

Numerous studies report that taking quercetin would protect against the risk of cardiovascular diseases, such as:

  • Hypertension.
  • Arrhythmias.
  • Myocardial stroke.
  • Coronary heart disease.

These pathologies are among the leading causes of death in Western countries. And they often have an excess of bad cholesterol (oxidized LDL) as their trigger.

LDL is in fact the first building block for platelet aggregation in the arteries, the cause of thrombi and arterial hypertension. Quercitin acts as an antioxidant, protecting low-density lipoproteins (LDL) from oxidation.

In doing so it limits the accumulation of oxidized LDL and platelet aggregation, with antithrombotic effects. Furthermore, it promotes relaxation of cardiovascular smooth muscles, with antihypertensive and antiarrhythmic effects.

To add points in its favour, recent studies demonstrate how quercetin and other flavonoids can directly modify the biosynthesis of eicosanoids (enzymes that regulate vasoconstriction). Thus acting as a natural antihypertensive.

Improve eyesight

The role of polyphenols in providing vision benefits has been known for some time. Quercetin (polyphenol-flavonol), like beta-carotene (polyphenol-carotene) may also be useful for improving vision. It all comes down to their antioxidant action.

Free radicals, in fact, contribute to the development of some vision disorders, including cataracts and macular degeneration of the retina. Quercetin can prevent these conditions by counteracting the action of free radicals.

Neuroprotective action

Several studies report how quercetin can exert a positive effect on the nervous system, which translates into improvements in mood, anxiety and depression, as well as memory and learning.

This flavonoid seems to have a neuroprotective and psychostimulant action of great importance for the scientific community, so much so that it can be implicated in the prevention of neurodegenerative diseases such as Alzheimer’s and Parkinson’s. But let’s go in order.

These effects are related to various mechanisms involving quercitin and nerve cell membranes. Here’s how it works to protect our nervous system:

  • It protects the nerve cell membrane from oxidative damage.
  • Strengthens the myelin sheath, essential for long-range nerve transmission.
  • Reduces inflammatory mediators.

How can it be useful for neurodegenerative therapies?

In particular, the antioxidant and anti-inflammatory activity of our flavonoid protects brain cells from oxidative stress, a process that itself causes neurodegenerative disorders (such as Parkinson’s and Alzheimer’s).

Quercitin appears to protect the dense neural network by inhibiting the formation of fibrillated beta-amyloid, the senile plaque found in the brains of people with Alzheimer’s.

Furthermore, this flavonol is a strong anti-inflammatory: it inhibits the secretion of mast cells, reduces the release of tryptase, IL-6 and histidine decarboxylase (HDC). Quercitin supplementation could therefore be a valid adjunct to L-dopa therapy in Parkinson’s disease.

Beneficial for the respiratory system

Perhaps you would not have thought of attributing this quality to quercetin. But this flavonoid may help prevent upper respiratory infections, seasonal colds, or even episodes of allergic rhinitis (inhalant allergy, hay fever) and hives.

In fact, quercitin inhibits the production and release of histamine and other pro-inflammatory substances involved both in the mechanism of the allergic response and in the defense against microorganisms causing infections.

Furthermore, improving your breathing will even increase your athletic performance (resistance and effort) for greater oxygenation of the muscle fibers.

Antimicrobial effect

There are numerous natural substances that have an antimicrobial effect. Among these there is also quercitin. But let’s take a step back.

By antimicrobials we mean those chemical or natural substances capable of killing (microbicidal action), or inhibiting the growth of microorganisms (static action). Antimicrobials can be divided according to their activity and the type of target (on which microorganism they act).

They are antimicrobial:

If they act by killing microorganisms, we are talking about: bactericides, fungicides and virocides. While, if their action is to block growth, we will have: bacteriostatic, fungistatic and virostatic.

Quercitin has been attributed both antiviral and antibacterial properties. In detail, it works by inhibiting the growth of almost all strains of bacteria that…