(Educational only)

Quercetin is a natural compound found in many fruits and vegetables. It helps the body in several ways—especially during cold and flu season. Studies show it may help your body fight infections and keep your immune system strong [1,2].

Quercetin has been tested against many viruses. Researchers found that it can slow down or block the tools viruses use to make more copies of themselves [3,4,5]. It can also stick to parts of the virus [6,7], making it harder for the virus to spread.

Quercetin moves through your digestive system without being broken down too quickly. It also acts as an antioxidant, which means it helps clean up harmful “free radicals”—tiny molecules that can damage cells.⁸⁹¹⁰

Some studies show that quercetin can interfere with how the hepatitis C virus makes new proteins and new virus particles [11,12,13]. It even blocks the virus from using fats inside the liver cell [14]

Quercetin has also been studied in people with COVID-19. In these studies, it helped improve symptoms and shorten hospital stays [11,16]. Researchers believe quercetin—especially when combined with vitamin C—may help block the virus from entering cells and making new virus copies [16].

Many COVID-19 complications are caused by free radicals, not just the virus itself. Quercetin helps protect the body from this damage [22].

Quercetin has shown antiviral activity against many other viruses too—including EBV, CMV, influenza, and herpes viruses such as HSV-1, HSV-2, and the virus that causes shingles (VZV) [18-23].

Bottom line: Quercetin may help the body defend itself from viruses and may lessen symptoms if you already have an infection. Click to learn more about quercetin.


Quercetin works even better when combined with vitamin C.

References:

  1. Curr Sports Med Rep. Jul-Aug 2009;8(4):206-13 Effects of the dietary flavonoid quercetin upon performance and health
  2. Eur J Pharmacol. 2008 May 13;585(2-3):325-37. Health effects of quercetin: from antioxidant to nutraceutical
  3. Inhibitory effect of flavonoids on DNA-dependent DNA and RNA polymerases. Experientia. (1988) 44:882–5
  4. Suppression of hepatitis C virus by the flavonoid quercetin is mediated by inhibition of NS3 protease activity. J Viral Hepat. (2012) 19:e81–8
  5. Inhibition of reverse transcriptases by flavonoids. Antiviral Res. (1989) 12:99–110
  6. Antimicrobial activity of flavonoids. Int J Antimicrob Agents. (2005) 26:343–56
  7. Effects of propolis flavonoids on virus infectivity and replication. Microbiologica. (1990) 13:207–13
  8. Peroxidase-catalyzed formation of quercetin quinone methide-glutathione adducts. Arch Biochem Biophys. (2000) 378:224–33
  9. Dietary flavonoids as antioxidants in vivo: conjugated metabolites of (-)-epicatechin and quercetin participate in antioxidative defense in blood plasma. J Med Invest. (1999) 46:159–68
  10. Confirmatory studies on the antioxidant and antidiabetic effect of quercetin in rats. Indian J Clin Biochem. (2010) 25:188–92
  11. Possible therapeutic effects of adjuvant quercetin supplementation against early‐stage COVID‐19 infection: A prospective, randomized, controlled, and open‐label study. International Journal of General Medicine, 14, 2359–2366. 10.2147/IJGM.S318720
  12. Suppression of hepatitis C virus by the flavonoid quercetin is mediated by inhibition of NS3 protease activity. Journal of Viral Hepatitis, 19, e81–e88. 10.1111/j.1365-2893.2011.01507.x
  13. Modulation of PI3K‐LXRα‐dependent lipogenesis mediated by oxidative/nitrosative stress contributes to inhibition of HCV replication by quercetin. Laboratory Investigation, 94, 262–274. 10.1038/labinvest.2013.156
  14. Modulation of PI3K‐LXRα‐dependent lipogenesis mediated by oxidative/nitrosative stress contributes to inhibition of HCV replication by quercetin. Laboratory Investigation, 94, 262–274. 10.1038/labinvest.2013.156
  15. Naringenin and quercetin—Potential anti‐HCV agents for NS2 protease targets. Natural Product Research, 30, 464–468. 10.1080/14786419.2015.1020490
  16. Immunol., 19 June 2020 Quercetin and Vitamin C: An Experimental, Synergistic Therapy for the Prevention and Treatment of SARS-CoV-2 Related Disease (COVID-19)
  17. Modulation of PI3K‐LXRα‐dependent lipogenesis mediated by oxidative/nitrosative stress contributes to inhibition of HCV replication by quercetin. Laboratory Investigation, 94, 262–274. 10.1038/labinvest.2013.156
  18. Eight flavonoids and their potential as inhibitors of human cytomegalovirus replication. Antiviral Research, 96, 181–186. 10.1016/j.antiviral.2012.09.010
  19. The anti‐HSV‐1 effect of quercetin is dependent on the suppression of TLR‐3 in raw 264.7 cells. Archives of Pharmacal Research, 40, 623–630. 10.1007/s12272-017-0898-x
  20. Quercetin interrupts the positive feedback loop between STAT3 and IL‐6, promotes autophagy, and reduces ROS, preventing EBV‐driven B cell immortalization. Biomolecules, 9(9), 482. 10.3390/biom9090482
  21. Antiviral activities of quercetin and isoquercitrin against human herpesviruses. Molecules, 25(10), 2379. 10.3390/molecules25102379
  22. Quercetin interrupts the positive feedback loop between STAT3 and IL‐6, promotes autophagy, and reduces ROS, preventing EBV‐driven B cell immortalization. Biomolecules, 9(9), 482. 10.3390/biom9090482
  23. Uirusu, 62, 219–228. 10.2222/jsv.62.219
  24. Phytother Res. 2021 Oct 28;36(1):266–278. Quercetin and its derivates as antiviral potentials: A comprehensive review