September 26, 2022

Quercetin: My Fav Flav(onoid)

Quercetin is a bioflavonoid, a plant-derived compound that offers a myriad of health benefits.  Found ubiquitously in nature, you can increase your intake of quercetin by emphasizing fruits, vegetables, nuts, and seeds in the diet.  Research has shown that quercetin has anti-inflammatory, immune-supportive, and antioxidant properties,1 to name just a few.

In recent times, quercetin has been studied for its potential in preventing and treating SARS-CoV-2 (the novel coronavirus or COVID-19) by way of various mechanisms.  These include inhibiting the inflammatory response1, preventing blood clots,2 and improving clearance of the virus.   To date, studies have supported the use of quercetin in COVID-19 treatment both alone as well as in combination with zinc, vitamin C, curcumin, vitamin D3, and a variety of over-the-counter drugs and pharmaceuticals, including Tylenol3 and hydroxychloroquine.2   One such study reported that a multi-drug approach with quercetin and vitamin C may help to disrupt the entry of the virus, viral replication, and various enzymes that play a role in this process.  In fact, a body of research suggests that these nutrients administered together may have implications in other respiratory illness, such as influenza (“the flu”).   In the case of the novel coronavirus, early treatment is imperative to avoid hospitalization and reduce the severity of disease. 4

Some studies have reported faster recovery time and a decrease in hospitalization time of COVID-19 patients with the use of quercetin.3  A 2021 clinical trial published in the International Journal of General Medicine compared two randomized groups of forty-two COVID-19 positive individuals with mild disease.  One group was treated with the standard of care as established by hospital guidelines (anti-fever and antibiotic drugs for 3 days), and the other was treated with the standard of care plus quercetin (drugs and quercetin for 3 days, with quercetin dosing continuing to day 14 of the 2-week trial).  It was reported that those in the quercetin group demonstrated significant increases in viral clearance, reduced symptom occurrence, and improved disease biomarkers.  These markers, both related to inflammation and associated with COVID-19 severity, included lactate dehydrogenase (LDH) and ferritin.  Although not statistically significant, the study also reported reduced C-reactive protein (CRP) and D-dimer, markers of inflammation and blood clotting, respectively.  Quercetin was also very well-tolerated.  Side effects reported were no different than those of the drug-only group.3

 Another 3-month-long study published in 2022 investigated quercetin’s efficacy in the prevention of COVID-19 in healthcare workers.  Of the 120 subjects, half received 250 mg of quercetin twice daily and the other half were given placebo.  Every 3 weeks, subjects underwent rapid COVID-19 tests.  Researchers reported 1 of 60 subjects in the quercetin group and 4 of 60 subjects in the control group contracted COVID-19.  Complete symptom resolution was observed at 7 days in the quercetin group versus 15 days in the placebo group.  Their analyses concluded that those in the placebo group were at 14 times the risk of COVID-19 infection compared to the quercetin-treated group.5   Although quercetin’s efficacy remains questionable in the high-risk population,2 the evidence available appears promising for those at average risk.

Moreover, quercetin has positive effects on the gut microbiome, modulating imbalances that contribute to systemic inflammation.1  Given that holistic methods always emphasize a healthy gut, these multidimensional effects further support the use of quercetin in clinical practice.  Having various therapeutic roles, it fosters a minimalist yet comprehensive approach.

It is worth noting that not all quercetin-containing foods and supplements are created equal.  Because it is lipophilic, or “fat-loving,” supplements must be carefully formulated to enhance bioavailability2; That is, to be most effectively absorbed.  The poor absorption of quercetin itself has been measurably overcome by producing quercetin phytosomes, complexes of quercetin with a fat.  Often, the fatty substance used is lecithin, which can be found in foods like eggs and soybeans.6  Likewise, food sources of quercetin differ in absorbability.  For example, a 2012 study found that onion-derived quercetin was better absorbed than quercetin from apples.7

In conclusion, quercetin has potential for use in the treatment of COVID-19 illness.  Many factors such as severity of disease, dose, and bioavailability may affect the studied outcomes.  Further research and longer-term studies with larger cohorts are warranted to substantiate the available evidence.

 

References

  1. Imran M, Thabet HK, Alaqel SI, et al. The Therapeutic and Prophylactic Potential of Quercetin against COVID-19: An Outlook on the Clinical Studies, Inventive Compositions, and Patent Literature.Antioxidants (Basel). 2022;11(5):876. Published 2022 Apr 29. doi:10.3390/antiox11050876
  2. Colunga Biancatelli RML, Berrill M, Catravas JD, Marik PE. Quercetin and Vitamin C: An Experimental, Synergistic Therapy for the Prevention and Treatment of SARS-CoV-2 Related Disease (COVID-19).Front Immunol. 2020;11:1451. Published 2020 Jun 19. doi:10.3389/fimmu.2020.01451
  3. Saeedi-Boroujeni, A., Mahmoudian-Sani, MR. Anti-inflammatory potential of Quercetin in COVID-19 treatment.J Inflamm. 2021;18(3). Published 2021 Jan 28. https://doi.org/10.1186/s12950-021-00268-6
  4. Di Pierro F, Iqtadar S, Khan A, et al. Potential Clinical Benefits of Quercetin in the Early Stage of COVID-19: Results of a Second, Pilot, Randomized, Controlled and Open-Label Clinical Trial.Int J Gen Med. 2021;14:2807-2816. Published 2021 Jun 24. doi:10.2147/IJGM.S318949
  5. Rondanelli M, Perna S, Gasparri C, et al. Promising Effects of 3-Month Period of Quercetin Phytosome®Supplementation in the Prevention of Symptomatic COVID-19 Disease in Healthcare Workers: A Pilot Study. Life (Basel). 2022;12(1):66. Published 2022 Jan 4. doi:10.3390/life12010066
  6. Riva A, Ronchi M, Petrangolini G, Bosisio S, Allegrini P. Improved Oral Absorption of Quercetin from Quercetin Phytosome®, a New Delivery System Based on Food Grade Lecithin.Eur J Drug Metab Pharmacokinet. 2019;44(2):169-177. Published 2018 Oct 16. doi:10.1007/s13318-018-0517-3
  7. Kaşıkcı M. B, Bağdatlıoğlu N. Bioavailability of Quercetin. Curr Res Nutr Food Sci 2016;4(Special Issue Confernce October 2016). Published 2016 Jul 10. doi: http://dx.doi.org/10.12944/CRNFSJ.4.Special-Issue-October.20