The polyphenol quercetin 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. Quercetin has been shown to offer strong antioxidant and anti-inflammatory benefits, along with anti-hypertensive, anticoagulant, and anti-hyperglycemic properties.
A previous study demonstrated that quercetin could help protect patients from dying from severe complications associated with the H1N1 influenza A virus; however, the exact mechanism was unknown.
In a study published in Viruses, researchers investigated the effects of quercetin as an anti-viral agent. The impact of viruses vary. They can cause seasonal outbreaks and, as we are now seeing with COVID-19, a worldwide pandemic that impacts public health as well as the economy. There have been several other highly impactful 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, being an antioxidant and having anti-inflammatory properties, quercetin helps reduce the expression of pro-inflammatory cytokines and lung inflammation in mice.
As a result, quercetin may be an inexpensive yet effective natural polyphenol, providing support during influenza infections. It may also be considered in combination with other therapeutics and drugs, which could support their anti-viral effect while helping reduce drug dosage and side effects. Dosage range for quercetin supplementation is often between 200 mg to 1200 mg. Other compounds with potential anti-viral properties include vitamins A, C, and D, zinc, monolaurin, melatonin, resveratrol, and geranylgeraniol. Vitamin C specifically has been shown to enhance the absorption of quercetin and increase plasma levels.
By Michael Jurgelewicz, DC, DACBN, DCBCN, CNS