Quercetin is a very interesting substance made by a large number of plants, and notably by fruits, vegetables and herbs. It is one of a class of compounds termed Flavonoids. Flavonoids are pigments produced by plants to protect themselves against injury, deter insects, prevent infections, and to reflect away sunlight.

As powerful antioxidants, flavonoids protect a plant’s leaves against oxygen free radicals released during photosynthesis, when the green chlorophyll traps light photons and converts them into chemical energy. As autumn leaves die, the chlorophyll breaks down and the protective red and yellow flavonoids become visible.

Most flavonoids are very brightly coloured. The flavonoid curcumin in turmeric is intensely yellow; that in marigold petals is orange; red flavonoids can be seen in some grapes, and blue flavonoids in most berries. Plants take advantage of these pigments to add additional roles: colouring their flowers to attract pollinators and colouring their fruit to attract animals which will eat the fruit and disperse their seeds.

Quercetin is a bright yellow flavonoid with many useful nutritional properties. Antioxidant, anti-inflammatory and anti-allergic activities have been recognised for decades. Plants of course benefited from these; at least until we ate the plants and took the benefits for ourselves!

But these are not the only valuable qualities of quercetin. In animal and human studies, scientists have demonstrated antiviral actions. Let’s look at each in turn.

Antioxidant activity.

Oxygen free radicals are highly reactive compounds formed in the burning process. Within body cells, the mitochondria are the microscopic energy producers which take sugars and fats, burn them in oxygen, and trap the released energy within molecules of ATP, the body’s energy currency. This process releases quantities of reactive oxygen compounds which can easily damage cells, tissues, and even precious DNA.

Free radical scavengers such as quercetin effectively mop up and neutralise these radicals and protect the cells and tissues.

Quercetin also binds to metal ions. We have many metals in blood and tissues. Some of these are essential, for example iron and copper. Others are toxic; think of lead and arsenic. Metals are highly reactive substances and therefore produce free radicals. By binding to metals, quercetin inhibits reactions and thus reduces free radical generation.

Anti-inflammatory activity.

Inflammation is the natural response of the body to injury or infection. Inflammation triggers immune activation, tissue repair, and increased blood flow to transport white blood cells and nutrients to an infected or damaged area. However, inflammation also involves oxidative bursts and free radical generation by immune cells. Thus, excessive inflammation itself causes tissue damage and illness.

Inflammation is initiated and controlled by inflammatory mediators called eicosanoids. These are manufactured by two enzymes known as COX-1 and COX-2.

Quercetin inhibits both enzymes, and additionally protects immune cells from the oxidative burst, thus decreasing inflammation and reducing acute and chronic tissue damage.

Anti-allergic activity.

In classic allergy, an allergen triggers immune cells called mast cells and basophils to release inflammatory mediators such as cytokines and interleukins. These can stimulate rapid and sometimes severe inflammation.

Quercetin has been shown to stabilise mast cells and basophils, inhibiting the release of the mediators. It also appears to reduce the production of cytokines and interleukins in those cells, further reducing allergic inflammation.

European studies with people suffering symptoms of seasonal allergy showed that supplementation with quercetin, combined with standard therapy, could reduce symptoms by up 50% in the daytime and up to 70% at night.

Antiviral activity.

Intense physical exercise, even in athletes, is strongly associated with an increased rate of contracting colds or flu in the weeks following. Trained cyclists were given quercetin or placebo before, during and after a 3-day intense training session. The session was approximately twice as hard as their normal training. In the 2 weeks after the session, 1 of 20 in the supplemented group caught cold while 14 of 20 in the placebo group caught cold. However, in this study there was no difference in immune function between the groups on any of the measured functions. The researchers concluded that quercetin may have prevented post-exercise fall in immune function, while acting directly against the infectious virus.

In vitro studies have demonstrated that quercetin may reduce the frequency and symptoms of colds by inhibiting replication of several cold viruses, including flu virus, adenovirus, and rhinovirus.

So, if quercetin is so good, what’s the catch? It has very poor bioavailability. As it is not soluble in water or in lipids, as little as 2-17% can be absorbed from the digestive tract. (The absorption is improved if Vitamin C is taken at the same time).  This means very little of the dose taken is available for use within the body. For that reason, high doses, typically 1000 – 2000mg per day, are needed to achieve good effects.

Indena produces medical-grade herbal extracts. Recognising that many valuable herb components are poorly soluble, Indena developed technology to render them more bioavailable. Quercetin is finely ground and dispersed into sunflower seed lecithin. The mixture is stabilised with two typical tablet excipients, maltodextrin and silicon dioxide.

This is Quercefit® Human testing has shown that a single dose of 250mg of Quercefit® produces 10 times more quercetin in the bloodstream than does 500mg of plain quercetin.

Indena has also demonstrated that Quercefit® optimises athletic performance and improves recovery after exercise. Quercefit® combined with standard care also reduces symptoms of some viral infections and hastens vital clearance after infection.