Quercetin

The Science

Quercetin

Quercetin belongs to a group of plant compounds called bioflavonoids. Like all bioflavonoids, it acts as an antioxidant and scavenges free radicals in the body. It also helps to reduce inflammation, which causes oxidative cell damage and a host of other health issues. Initially, quercetin was considered to be a vitamin and was given the name “Vitamin P”. 

Quercetin

Occurrence in Food & Supplements

Quercetin is a plant pigment (bioflavonoid) that is found in many plants and foods, such as berries, apples, onions, green tea and red wine. Because our bodies cannot make quercetin, it must come from the foods (and supplements) that we eat every day.

Absorption & Bioavailability

Quercetin is popular supplement but, on its own, it is not easily absorbed or utilised within the body. However, according to Nutritionist, Amy Shapiro, “When paired with vitamin C, it is more potent [in the body] and vitamin C helps to regenerate quercetin within the body” (Amy Shapirio)

Safe Daily Level

You can get plenty of quercetin from eating a diet rich in fruit and vegetables, however, if you prefer to take a supplement, doses of 500-1000mg a day are considered safe (PubMed). There is no information about use of quercetin during pregnancy or while breastfeeding, so please consult your doctor.

Quercetin Health Benefits

  • “Quercetin… has unique biological properties that may improve mental/physical performance and reduce infection risk. These properties form the basis for potential benefits to overall health and disease resistance, including anti-carcinogenic, anti-inflammatory, antiviral, antioxidant…” (Journal of Nutrients)
  • “Quercetin… is well known to ameliorate chronic diseases and aging processes in humans, and its antiviral properties have been investigated in numerous studies… There is evidence that quercetin in combination with, for example, vitamins C and D, may exert a synergistic antiviral action.” (Sage Journals)
  • “Quercetin, a plant flavonoid blocks viral replication in vitro… In addition [it] inhibits virus-stimulated cytokine expression. [It] also inhibits viral replication and decreases lung inflammation.” (Antiviral Research)

Further Information

Quercetin

“Quercetin, a naturally occurring dietary flavonoid, is well known to ameliorate chronic diseases and aging processes in humans, and its antiviral properties have been investigated in numerous studies.” (SagePub)

Quercetin is also known for its antioxidant, anti-inflammatory, anti-allergic and anti-viral, and perhaps even anti-cancer properties, and for its ability to support the immune system.

Quercetin aids the absorption of Zinc into cells

We have already learnt how Quercetin and Vitamin C work together to improve each other’s absorption into the body. Well, it has a similar synergistic relationship with zinc too. Quercetin is known as a “zinc ionophore”, which means it enhances the absorption of zinc into the body’s cells. In simple terms, it “holds the door open” for the zinc to enter into our cells. (Journal of Agricultural and Food Chemistry)

Quercetin enhances the absorption of zinc, and both have anti-viral functions. Zinc is a positively charged ion, so it has difficulty passing through the fat soluble cell membrane. This  means zinc needs a “transporter” (ionophore) to help it to cross the cell membrane. Many fat-soluble nutrients can do this, but quercetin is a particularly effective, and may also enhance the antiviral properties of zinc. Please read our information about Zinc to learn more about the crucial role it plays in the human immune system, particularly in fighting off viruses.

Scientific References

“In our study, we found quercetin possessed anti-influenza activity. The subsequent mechanism study indicated quercetin showed inhibitory effect during virus entry. Then we found quercetin interacted with influenza hemagglutinin protein and then inhibited viral-cell fusion.”
Wu, Wenjiao et al. “Quercetin as an Antiviral Agent Inhibits Influenza A Virus (IAV) Entry.” Viruses vol. 8,1 6. 25 Dec. 2015, doi:10.3390/v8010006

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“Quercetin, a potent antioxidant and anti-inflammatory agent, also possesses anti-rhinoviral effects. Quercetin inhibits viral infection at multiple stages”.
Ganesan S, Faris AN, Comstock AT, et al. Quercetin inhibits rhinovirus replication in vitro and in vivo. Antiviral Research. 2012 Jun;94(3):258-271. DOI: 10.1016/j.antiviral.2012.03.005. PMID: 22465313; PMCID: PMC3360794.

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“Quercetin is known to exhibit antibacterial effects against almost all strains of bacteria, particularly affecting gastrointestinal, respiratory, urinary, and dermal system. Their anti-infective and anti-replicative ability possibly contributes to the antiviral characteristics.”
Anand David, Alexander Victor et al. “Overviews of Biological Importance of Quercetin: A Bioactive Flavonoid.” Pharmacognosy reviews vol. 10,20 (2016): 84-89. doi:10.4103/0973-7847.194044

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