From MEpedia, a crowd-sourced encyclopedia of ME and CFS science and history

Quercetin is one of many flavonoids found in plant pigments, being orange to orange-yellow in color. It is the principal source flavonoid in human nutrition and is commonly used in food processing.[1] Quercetin is found in high concentrations in asparagus, red onions, broccoli and buckwheat.

Other names for quercetin include: Citrus bioflavonoid, Sophoretin; Meletin; Quercetine; Xanthaurine; Quercetol; Quercitin; Quertine; Flavin.[2][3]

Function[edit | edit source]

Quercetin affects immunity and inflammation by acting mainly on leukocytes and targeting many intracellular signaling kinases and phosphatases, enzymes and membrane proteins often crucial for cellular specific function.[4] [5]

Food sources[edit | edit source]

Quercetin can be found in many foods including red onions, red wine, onions, green tea, apples, asparagus, berries, broccoli and Brassica vegetables, kale, ginkgo biloba, St. John's Wort, American elder, and buckwheat tea.[1][6]

Health uses[edit | edit source]

Quercetin supplements are often promoted for

However, many of these uses have weak evidence supporting them, and for some uses there is evidence that quercetin supplementation do not improve symptoms.[1]

Quercetin is also taken by athletes to increase endurance and improve performance.[1]

Quercetin is a potent antioxidant.[5] Most of the information on flavonoids concerns quercetin because with only sight changes to the backbone of flavones and subtle cell behavior mechanisms and responsiveness, flavoinoids can be modulating, biphasic and exert regulatory action on immunity and inflammation. Only a few flavones and flavonols have been assayed mainly due to chemical similarity to quercetin.[4]

Safety[edit | edit source]

The US FDA has issued warning letters to manufacturers of supplements containing quercetin to withdraw health benefit claims and emphasize that quercetin is not a defined nutrient nor an antioxidant, cannot be assigned a dietary content level and is not regulated as a drug to treat any human disease.[8]

The European Food Safety Authority evaluated possible health claims associated with consumption of quercetin, and found that no cause-and-effect relationship established for any physiological effect in human health or diseases.[9]

Chronic fatigue syndrome[edit | edit source]

Quercetin's antioxidant and anti-inflammatory properties are thought to be important in resolving the pathophysiology of ME/CFS. Additionally, a 2009 study by J. Mark Davis, et al. (2008)[10] showed markers of mitochondrial biogenesis in mouse skeletal muscle and brain, and on endurance exercise tolerance after a week of quercetin in their food.

Luteolin is another flavonoid antioxidant which is common place.

Flavonoids are believed to be poorly absorbed due to bring rapidly metabolized and excreted. There remains no evidence that polyphenols (of which flavonoids are subset of) have any relevance on the body.

Additionally, although antioxidants in the diet are required to be healthy, there is considerable debate on which antioxidants are health promoting, in what amounts and if they can prevent or help chronic diseases.

Depression[edit | edit source]

Quercetin acts to inhibit the enzyme monoamine oxidase (MAO), an enzyme that breaks down the mood-influencing neurotransmitters serotonin, dopamine and norepinephrine,[6] although clinical trials in humans are lacking.

See also[edit | edit source]

Learn more[edit | edit source]

References[edit | edit source]

  1. 1.0 1.1 1.2 1.3 1.4 "Quercetin: Uses, Side Effects, Interactions, Dosage, and Warning". webmd.com. Retrieved May 5, 2020.
  2. PubChem. "Quercetin". pubchem.ncbi.nlm.nih.gov. Retrieved May 5, 2020.
  3. "Quercetin Uses, Benefits & Dosage - Drugs.com Herbal Database". Drugs.com. Retrieved May 5, 2020.
  4. 4.0 4.1 Chirumbolo, Salvatore (September 2010), "The role of quercetin, flavonols and flavones in modulating inflammatory cell function", Inflammation & Allergy Drug Targets, 9 (4): 263–285, ISSN 2212-4055, PMID 20887269
  5. 5.0 5.1 Balavoine, G.G.; Geletii, Y.V. (1999), "Peroxynitrite scavenging by different antioxidants. Part I: convenient assay", Nitric Oxide: Biology and Chemistry, 3 (1): 40–54, doi:10.1006/niox.1999.0206, ISSN 1089-8603, PMID 10355895
  6. 6.0 6.1 "Food and Mood: Eating Plants to Fight the Blues". Physicians Committee for Responsible Medicine. Retrieved March 26, 2021.
  7. 7.0 7.1 https://www.researchgate.net/profile/Karen-Hirsch-Ernst/publication/321014123_Safety_Aspects_of_the_Use_of_Quercetin_as_a_Dietary_Supplement/links/5c03d507a6fdcc1b8d502a93/Safety-Aspects-of-the-Use-of-Quercetin-as-a-Dietary-Supplement.pdf
  8. FDA's Electronic Reading Room - Warning Letters
  9. European Food Safety Agency (EFSA) NDA Panel (Dietetic Products, Nutrition and Allergies) (8 April 2011).
  10. Davis, J. Mark; Murphy, E. Angela; Carmichael, Martin D.; Davis, Ben (April 1, 2009), "Quercetin increases brain and muscle mitochondrial biogenesis and exercise tolerance", American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, 296 (4): 1071-R1077, doi:10.1152/ajpregu.90925.2008, ISSN 0363-6119, PMID 19211721, retrieved November 9, 2016