Flavonoids, are “indispensable” pigments found in plants like fruits, vegetables, grains, roots, stems, flowers and leaves with great potential for the prevention and treatment of disease because of their anti-oxidative, anti-inflammatory, anti-mutagenic and anti-carcinogenic properties (1,2,3,6) Very simply put, these tiny compounds are what help protect the plants themselves from stressors, and when we eat them, we get offered protection in a similar way.
Flavonoids are assigned different subgroups based on their chemical structure: anthocyanins, flavanols, flavanones, flavones, and isoflavones, and there are about 6000 known varieties (6) with more constantly being discovered, which is yet another reason why getting a diverse variety of plants in your diet each day is so very important – to cover as many bases as possible.
Quercetin is considered to be one of the most important flavonoids (4) (more specifically, a flavanol,) because it seems to offer the most powerful protection against reactive oxygen species (5) (oxidative stress). Probably for that reason, and also because it is the most common antioxidant available in common foods, (5) it is one of the most widely studied, and has been linked with heart health (7,18), brain health ( 8 ), bone health (7 ) lung health (7,17), cancer prevention, (7) immunity (3, 9,14), improved insulin sensitivity (13 ) and athletic performance (11, 12 ) in part through its powerful effect on chronic inflammation by neutralizing free radicals .
Because of its wide range of health, biological, antioxidant, anti-inflammatory, immune system regulation, and cardioprotective and neuroprotective effects (14), especially the supportive and regulatory roles it plays in immune function (14, 9, 3), Quercetin has received much attention over this last year in particular:
Quercetin has the potential to regulate the NLRP3 inflammasome ( 15)– a part of the innate immune system which may lead to uncontrolled release of pro-inflammatory cytokines, ‘cytokine storm’ and severe damage of the respiratory epithelium , ( 16 ) which the Sars-CoV-2 virus has been shown to activate (16), so it is currently of even more significant scientific interest.
Quercetin can be found in the following foods: capers, red apples, parsley, dark cherries, red/yellow onions, kale, tomatoes (cherry are best because of their skin/flesh ratio), dark berries, broccoli, grapes, and more). But it’s not wise to pick just one and eat a lot, and here’s why:
All these foods have different concentrations and different levels of bioavailability ( 1 ), which can vary from harvest to harvest.
Additionally, these flavonoids don’t work in isolation — there is a synergy between the various antioxidants themselves; for instance, The antioxidant activity of quercetin is mainly manifested largely by its effect on glutathione (one of the most important determinants of the antioxidant defense system) (19) whose levels it regulates in order to increase the body’s antioxidant potential (11)
So, your best bet is to try to eat a variety every day. Aim for the rainbow to cover as many bases as possible, and make your plate at least ½ veggies every meal. And if you can’t get that done consistently, consider bridging the gap with plant powders which have flavonoids like Quercetin (and thousands of others), and possibly adding an additional Quercetin supplement during these times.
There are no known contraindications for supplementing with quercetin (5), but there are some potential drug interactions (5) Felodipine, estradiol, Cyclosporine, Quinolones, Cisplatin, Doxorubicin, Digoxin so talk to your doctor before you begin.
1. Flavonoids–food sources and health benefits https://pubmed.ncbi.nlm.nih.gov/25272572/
2. Quercetin: potentials in the prevention and therapy of disease https://pubmed.ncbi.nlm.nih.gov/18827577/
3. Quercetin: Antiviral Significance and Possible COVID-19 Integrative Considerations https://journals.sagepub.com/doi/full/10.1177/1934578X20976293
5. Quercetin: A Versatile Flavonoid https://www.akspublication.com/Paper05_Jul-Dec2007_.pdf
6. Flavonoids: an overview https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5465813/
7. Health effects of quercetin: from antioxidant to nutraceutical https://pubmed.ncbi.nlm.nih.gov/18417116/
8. Role of Quercetin Benefits in Neurodegeneration https://link.springer.com/chapter/10.1007/978-3-319-28383-8_12
9. Quercetin reduces susceptibility to influenza infection following stressful exercise https://journals.physiology.org/doi/full/10.1152/ajpregu.90319.2008?hits=10&HITS=10&author1=McClellan%2C+JL&sortspec=relevance&searchid=1&maxtoshow=&FIRSTINDEX=0&resourcetype=HWCIT&RESULTFORMAT=
10. Flavonoids–food sources and health benefits https://pubmed.ncbi.nlm.nih.gov/25272572/
11. QUERCETIN IN HEALTH AND DISEASE https://www.rjor.ro/wp-content/uploads/2021/07/QUERCETIN-IN-HEALTH-AND-DISEASE.pdf
12. Quercetin phytosome® in triathlon athletes: a pilot registry study. https://europepmc.org/article/med/29947492
13. Quercetin Decreases Insulin Resistance in a Polycystic Ovary Syndrome Rat Model by Improving Inflammatory Microenvironment https://journals.sagepub.com/doi/full/10.1177/1933719116667218
14. Anti-inflammatory potential of Quercetin in COVID-19 treatment https://journal-inflammation.biomedcentral.com/articles/10.1186/s12950-021-00268-6
15. Natural Compounds as Regulators of NLRP3 Inflammasome-Mediated IL-1 β Production https://pubmed.ncbi.nlm.nih.gov/27672241/6
16. Severe Acute Respiratory Syndrome Coronavirus Viroporin 3a Activates the NLRP3 Inflammasome https://www.frontiersin.org/articles/10.3389/fmicb.2019.00050/full
17. DNA damage protection by bulk and nano forms of quercetin in lymphocytes of patients with chronic obstructive pulmonary disease exposed to the food mutagen 2-amino-3-methylimidazo [4,5-f]quinolone (IQ) https://www.sciencedirect.com/science/article/abs/pii/S0013935118302536
18. Dietary Quercetin and Kaempferol: Bioavailability and Potential Cardiovascular-Related Bioactivity in Humans https://www.mdpi.com/2072-6643/11/10/2288
19. Glutathione homeostasis is significantly altered by quercetin via the Keap1/Nrf2 and MAPK signaling pathways in rats https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5773830/