Plant-based antioxidants: do flavonoids offer antiviral protection?
(by Angela Spencer)


Angela Spencer is from Mount Waverley.

Covid-19 has triggered a resurgence in the hunt for pharmaceutical and natural-occurring antivirals. Some researchers are exploring the antiviral potential of plant-based flavonoids as an extra level of the defence while we await a safe vaccine. Flavonoids are produced by plants in response to pathogens and photosynthesis. These compounds are most abundant in the body of plants (roots, trunk and leaves) as they are designed to protect the plant against infection and damage from the sun. Flavonoids have a tonifying effect on humans, many with antiviral and anti-inflammatory properties. They are currently being studied in connection to healthy aging, allergies, diabetes and a range of other disorders related to inflection and inflammation.

The links below contain information on a wide range of studies into flavonoids and viruses. Those relating specially to Covid-19 are placed at the top and some of them are pre-prints as they are still under review.

  1. Xu et al. (2020). High expression of ACE2 receptor of 2019-nCoV on the epithelial cells of oral mucosa.
  2. Sheridan, K. (2020) The coronavirus sneaks into cells through a key receptor. Could targeting it lead to a treatment?
  3. Li et al (2016). Angiotensin-converting enzyme 2 prevents lipopolysaccharide-induced rat acute lung injury via suppressing the ERK1/2 and NF-?B signaling pathways.
  4. Tikellis, C., & Thomas, M-C. (2012). Angiotensin-converting enzyme 2 (ACE2) is a key modulator of the renin angiotensin system in health and disease.
  5. Zhang et al (2018). ACE-2/ANG1-7 ameliorates ER stress-induced apoptosis in seawater aspiration-induced acute lung injury.
  6. Yang et al (2020). Angiotensin II receptor blockers and angiotensin-converting enzyme inhibitors usage is associated with improved inflammatory status and clinical outcomes in Covid-19 patients With hypertension.
  7. Paredes et al (2018). Beneficial effects of different flavonoids on vascular and renal function in L-NAME hypertensive rats.
  8. Sui et al (2010). Effects of apigenin on the expression of angiotensin-converting enzyme 2 in kidney in spontaneously hypertensive rats.
  9. Guerrero et al (2012). Inhibition of angiotensin-converting enzyme activity by flavonoids: structure-activity relationship studies.
  10. Fauzi et al (2019). Interaction between green tea and perindopril reduces inhibition of angiotensin-converting enzyme activity.
  11. Khan et al (2020). Identification of dietary molecules as therapeutic agents to combat Covid-19 using molecular docking studies.
  12. Li et al (2000). Flavonoid baicalin inhibits HIV-1 infection at the level of viral entry.
  13. Zakaryan et al (2017). Flavonoids: promising natural compounds against viral infections.
  14. Yi et al (2004). Small molecules blocking the entry of severe acute respiratory syndrome coronavirus into host cells.
  15. Connel et al (2016). A cinnamon-derived procyanidin compound displays anti-HIV-1 activity by blocking heparan sulfate- and co-receptor- binding sites on gp120 and reverses T cell exhaustion via impeding Tim-3 and PD-1 Upregulation.
  16. Fauvelle et al (2007). A cinnamon-derived procyanidin type A compound inhibits hepatitis C virus cell entry.
  17. Chen et al (2005). Inhibition of SARS-CoV 3C-like protease activity by theaflavin-3,3′-digallate (TF3).
  18. Jo et al (2020). Inhibition of SARS-CoV 3CL protease by flavonoids.
  19. Schwartz et al (2014). Kaempferol derivatives as antiviral drugs against the 3a channel protein of coronavirus.
  20. Leardkamolkarn et al (2012). Development of dengue type-2 virus replicons expressing GFP reporter gene in study of viral RNA replication.
  21. Yang et al (2013). Comparison of in vitro antiviral activity of tea polyphenols against influenza A and B viruses and structure–activity relationship analysis.
  22. Kaihatsu et al (2018). Antiviral mechanism of action of epigallocatechin-3-O-gallate and its fatty acid esters.
  23. Dabbagh-Bazarbachi et al (2014). Zinc ionophore activity of quercetin and epigallocatechin-gallate: from hepa 1-6 cells to a liposome model.
  24. Fernandez-Palanca et al (2019). Antitumor effects of quercetin in hepatocarcinoma in vitro and in vivo models: a systematic review.
  25. Read et al (2019). The role of zinc in antiviral immunity.

  4 Responses to “Plant-based antioxidants: do flavonoids offer antiviral protection?
(by Angela Spencer)”

  1. Thanks for this article, Angela – it’s great to hear what we can do for ourselves to keep up our immunity. I hope this encourages people now and in the future to eat for health. Do you know where we can get high levels of flavinoids in food?

    • Thanks for taking interest, Marina.

      When looking for rich sources of flavonoids, your safest bet is the body of the plant.

      For example:
      Roots = ginger and tumeric
      Bark = cinnamon
      Leaves = herbs, tea.

      The most potent flavonoids against Covid-19 (according to reference 11 ‘Khan et al, 2020’) are found in green tea, turmeric, parsley, chamomile, oats and barley. It is important to note, however, when using food as medicine, quantity is important.
      Khan et al (Reference 11) outline dosage and frequency of foods containing the most effective flavonoids. Whilst it is a pre-print, the standards and practices used add to its validity. I will be updating the reference list as more evidence regarding Covid-19 specifically makes its way to the peer-reviewed bracket.

      Thanks again for your interest!

  2. I understand that in citrus, the flavinoids in the pith help the body absorb the Vitamin C in the flesh of the fruit. Nice to have them there together!

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