The ultimate guide to Quercetin

The ultimate guide to Quercetin

In recent times, Quercetin has grown in popularity from a lesser known supplement to one of high demand, and rightly so... Quercetin is one of the most powerful and abundant flavonoids consumed in the human diet. So what exactly is Quercetin?

Quercetin is actually a pigment that belongs to a group of compounds found in plants called flavonoids. It is found in a wide variety of fruits and vegetables and accounts for 75% of our daily flavonoid intake. Foods rich in quercetin include onions, apples, berries, citrus fruits, grapes, kale, buckwheat, broccoli, tomatoes, black tea and red wine. The concentration of Quercetin can however differs not only from plant to plant, but also depending on the part of the plant used, as well as the country it is grown in. Onion-derived Quercetin, for example, is known to have a higher bioavailability than Quercetin derived from apples.

Quercetin plays an important role in supporting a healthy immune response, reducing inflammation, and fighting free radicals and can also reduce the incidence of upper viral respiratory tract infections such as the common cold, after periods of intensive exercise or high stress load.

Quercetin is one of the most abundant antioxidants available in the human diet with an estimated average daily dietary intake between 10-100 mg daily. Antioxidants are compounds that are able to bind to free radicals in the body and effectively neutralise them. Free radicals are unstable molecules that can be found in our body and, if left to multiply, they can cause cellular damage. Free radical damage has been linked to a multitude of chronic conditions including cancer, diabetes and heart disease. Quercetin has been found to be more powerful as an antioxidant than vitamins C and E.


Quercetin exhibits anti-inflammatory activity through the inhibition of inflammatory enzymes such as cyclooxygenase (COX) and lipoxygenase (LOX) and it also reduces the effect of inflammatory mediators including prostaglandins and leukotrienes. Inflammation is a natural side-effect of the immune response, but excessive acute inflammation can interfere with an effective immune response and chronic unopposed inflammation can exacerbate disease leading to increased cellular damage and ill health.

Immune Function:

Quercetin has been found to exhibit immunomodulatory properties meaning it can positively influence immune function. It appears to stimulate T-helper cells that produce Th-1-derived Interferon-y (IFN-y) while down-regulating Th2-derived Interleukin-4. T-helper cells are said to be the most important cells in adaptive immunity, as they help to activate B cells, secrete antibodies, assist macrophages to destroy ingested microbes and also activate cytotoxic T cells that kill infected target cells. Adaptive immunity is often referred to as the acquired immune system and helps to eliminate pathogens or prevent their pathogenic growth.

The immunomodulatory effects of Quercetin have previously been demonstrated in human clinical trials which suggest it might help reduce the incidence of respiratory illness after intensive exercise. In double-blind conditions, supplemental doses of 1000mg of Quercetin taken for three weeks prior, during and for two weeks after a three-day period of intensive (3 hours per day) cycling event resulted in a lower incidence of upper respiratory tract infection amongst participating cyclists.

Interestingly, research also suggests that co-administration of vitamin C with Quercetin exerts a synergistic antiviral action due to the capacity of ascorbic acid (vitamin c) to recycle Quercetin into its active form, thereby increasing its effectiveness. Research has also found that Quercetin might exhibit direct antiviral properties by significantly reducing formation of plaque by RNA and DNA viruses by exerting anti-infective and anti-replicative properties.

Polyphenols, such as Quercetin and resveratrol are known to be exert anti-allergenic effects by blocking histamine release from basophils and mast cells. Quercetin also alters IgE-mediated release, a type of antibody made by the immune system in response to allergic reactions.


As an antioxidant, Quercetin acts as a scavenger of reactive oxygen and nitrogen species - highly reactive ions that are either generated through metabolic processes or following exposure to toxins, radiation or other exogenous sources. Accumulation of these molecules within the body can result in increased oxidative damage to DNA, proteins and lipids. Quercetin is able to form metal ion complexes to prevent further free radical generation. Oxidative damage within the body is known to contribute to chronic and degenerative conditions as well as cellular aging.


Natural bioavailability of Quercetin is generally considered to be low for therapeutic purposes due to its low solubility, poor absorption and rapid metabolism. However, certain forms of Quercetin, such as QU995 have considerable research indicating superior bioavailability and increased purity. QU995 has been granted GRAS status in the United States, meaning it is Generally Regarded as Safe. QU995 is sustainably sourced from Fava beans and is one of the purest Quercetin flavonoid polyphenols available in the market today. Fava beans are grown from plants grown in Brazil with the scientific names Dimorphandra mollis and Dimorphandra gardneriana.

Picture of Fava Beans in a low dish placed on a beige tea towel



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