Quercetin, a polyphenol, has been shown to have both strong antioxidant as well as anti-inflammatory properties. It is one of the ubiquitous flavonoids found in many Chinese herbs, fruits, and vegetables. Common foods include blueberries, red onions, broccoli, cauliflower, kale, and many nuts. Research has demonstrated that quercetin supplementation has anti-hypertensive, anticoagulant, and anti-hyperglycemic properties.

A previous study demonstrated that quercetin could protect patients from dying from severe complications associated with the H1N1 influenza A virus, however, the mechanism was unknown.

According to a study published in Viruses, researchers investigated the effects of quercetin as an anti-viral agent. There have been several other infections such as the H1N1 swine flu, H5N1 avian influenza, and H7N9 influenza virus, which can lead to acute respiratory distress syndrome, pulmonary compromise, and death. Due to the lack of drugs to treat these infections, natural compounds are a major area of anti-viral research discovery.

The life cycle of the influenza virus consists of viral attachment, entry, replication, and release.

This study demonstrated that quercetin can inhibit the entry of an influenza virus in the early stage of infection measuring the inhibition in a cell infection model. This is the initial step of the viral replication cycle. In addition, the research team noted that this inhibitory effect was increased when the virus was pre-incubated with quercetin. It is also important to note that quercetin being an antioxidant and having anti-inflammatory properties reduces the expression of pro-inflammatory cytokines and lung inflammation in mice.

As a result, quercetin may provide an inexpensive natural polyphenol for prevention and treatment of influenza infections. It may also be considered in combination with other therapeutics and drugs, which could have an increased anti-viral effect, reduce drug dosage, and fewer side effects. As a dietary supplement, quercetin is often consumed between 200 mg to 1200 mg. Other anti-viral compounds to consider include vitamins A, vitamin C, vitamin D, zinc, monolaurin, melatonin, resveratrol, and geranylgeraniol.  Vitamin C specifically has been shown to improve the absorption of quercetin and increase plasma levels.

 By Michael Jurgelewicz, DC, DACBN, DCBCN, CNS

Source: Wu Wenjiao, Li Richan, et al. Quercetin as an Antiviral Agent Inhibits Influenza A Virus (IAV) Entry. Viruses. 25 December 2015;8(1).

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