Found in many fruits and vegetables, quercetin may have some potential in the context of aging. We take a look at this natural compound and popular dietary supplement.
What is quercetin?
Quercetin is a natural flavonoid, which makes it part of a large family of water-soluble plant compounds. Flavonoids are not created by the body and are an important part of a healthy diet.
Albert Szent-Györgyi discovered flavonoids in 1936 while researching ways to treat scurvy. He won the Nobel Prize in 1937 for his “discoveries in connection with the biological combustion processes with special reference to vitamin C and the catalysis of fumaric acid”.
We have much to thank him for, especially his discovery of the flavonoids, particularly quercetin. Flavonoids were once known as vitamin P for permeability. This was because some flavonoids can influence the permeability of blood vessel walls.
What does quercetin do?
It is one of the most common antioxidants found in our diets and plays a key role in reducing damage to cells from free radicals.
Besides its antioxidant properties, it may have broader anti-inflammatory properties. It reduces the activity of nuclear factor kappa B (NF-κB), a pro-inflammatory molecule. It also appears to reduce the inflammatory response of macrophages.
Quercetin in foods
Quercetin is present in a variety of fruits and vegetables.
|Food||Quercetin (mg per 100 g)|
|Raw Hot/yellow peppers||50.73|
|Raw red onions||39.21|
|Raw Hot/green peppers||14.7|
|Raw red leaf lettuce||7.61|
|Raw white onions||6.17|
|Golden delicious apples||3.69|
|Raw sweet cherries||2.29|
If you are struggling to get enough quercetin in your diet, you can also get a quercetin supplement. It is readily available and at a relatively low cost.
Isoquercetin (also known as isoquercitrin) is related to quercetin and has better bioavailability . It is harder to get than regular quercetin and may be more expensive, though smaller amounts are required as it is around 6 times more potent.
Potential quercetin health benefits
There are some potential health benefits related to quercetin.
Quercetin is an antioxidant
Quercetin has shown antioxidant properties by neutralizing and scavenging reactive oxygen and nitrogen species [2-3]. Our bodies produce free radicals as a byproduct of our mitochondria making energy, which is likely to be one of the reasons we age.
It also has anti-bacterial [4-5], anti-inflammatory , and anti-carcinogenic [7-12] properties.
Quercetin supports efficient protein production
Quercetin has the ability to enhance proteolysis and maintain proteostasis [13-14]. Proteostasis ensures that proteins are created and folded correctly before use in the cell. The loss of proteostasis leads to misfolded proteins and is another reason we age.
Quercetin appears to support the brain and immune system
Old mice given quercetin showed improved general and spatial awareness . The same mice also had an increased level of exploratory behavior, typically seen in younger mice.
Another study showed an improvement of the immune cells of artificially aged mice . While these mice are not an exact emulation of aging, they do provide useful data for studying aging.
Quercetin may slow down skin aging
Topical treatment increases the hydration and elasticity of the skin, reducing wrinkles . The skin is also easy to access, unlike internal organs, making it an ideal target for anti-aging studies using flavonoids.
Quercetin has also shown efficacy in treating skin disorders such as dermatitis [18-20].
Quercetin may improve NAD+ levels
It reduces inflammation and increases NAD+ levels by reducing inflammatory factors such as CD38 [21-23]. NAD+ is in every cell, interacts with sirtuins to regulate metabolism, and plays a role in health and longevity. CD38 increases with age and consumes NAD+, making our metabolism increasingly dysfunctional.
Quercetin as a senolytic
As we age, increasing amounts of dysfunctional, non-dividing senescent cells accumulate. These damaged cells are normally removed by the immune system, but as we age, this system declines and more and more of these cells build up. Senescent cell accumulation is one of the reasons we age.
Senescent cells secrete a cocktail of pro-inflammatory signals known as the senescence-associated secretory phenotype, or SASP . The SASP generates chronic levels of inflammation and an altered cell-to-cell signaling environment. This persistent inflammation, called “inflammaging”, is believed to be one of the drivers of aging [25-26].
Senolytics are compounds that can induce senescent cells enter apoptosis. Inducing this cellular self destruct could be a potential way of dealing with accumulated senescent cells.
Quercetin reduces inflammation by inhibiting some elements of the SASP. It can also directly induce apoptosis when used in combination with other drugs to improve vascular health [27-28].
Quercetin may reduce blood pressure
It has shown promise in reducing blood pressure, with some positive results for people with hypertension . A detailed meta-analysis on quercetin and blood pressure was also conducted .
Quercetin side effects
No serious adverse effects have been reported, and studies have shown that it can be taken safely up to 500 mg twice daily for 12 weeks. Longer-term use and higher doses remain an unknown at this time. Some people may experience headaches, stomach aches, or tingling sensations if taking more than 1000 mg of quercetin in a day. As with all supplements, if you do experience adverse effects, you should cease taking it and consult your doctor.
This article is only a very brief summary. It is not intended as an exhaustive guide and is based on the interpretation of research data, which is speculative by nature. This article is not a substitute for consulting your physician about which supplements may or may not be right for you. We do not endorse supplement use or any product or supplement vendor, and all discussion here is for scientific interest.
 Paulke, A., Eckert, G.P., Schubert-Zsilavecz, M., & Wurglics, M. (2012). Isoquercitrin provides better bioavailability than quercetin:comparison of quercetin metabolites in body tissue and brain sections after six days administration of isoquercitrin and quercetin. Die Pharmazie-An International Journal of Pharmaceutical Sciences, 67(12), 991-996.
 Hanasaki, Y., Ogawa, S., Fukui, S. (1994). The correlation between active oxygens scavenging and antioxidative effects of flavonoids.Free Radical Biology and Medicine, 16(6), 845-850.
 Van Acker, S.A., et al. (1996). Structural aspects of antioxidant activity of flavonoids. Free Radical Biology and Medicine, 20(3), 331-342.
 Boots, A.W., Haenen, G.R., Bast, A. (2008). Health effects of quercetin:from antioxidant to nutraceutical.European Journal of Pharmacology, 585(2), 325-337.
 Cushnie, T.T., Lamb, A.J. (2005). Antimicrobial activity of flavonoids. International Journal of Antimicrobial Agents, 26(5), 343-356.
 Sen,G.,Biswas,D.,Ray,M.,Biswas,T.(2007). Albumin–quercetin combination offers a therapeutic advantage in the prevention of reduced survival of erythrocytes in visceral leishmaniasis. Blood Cells,Molecules,and Diseases,39(3),245-254.
 Oršolić, N., et al. (2004). Immunomodulatory and antimetastatic action of propolis and related polyphenolic compounds. Journal of Ethnopharmacology, 94(2), 307-315.
 Gulati, N., et al. (2006). The antiproliferative effect of Quercetin in cancer cells is mediated via inhibition of the PI3K-Akt/PKB pathway. Anticancer Research, 26(2A), 1177-1181.
 Kuo, S.M. (1996). Antiproliferative potency of structurally distinct dietary flavonoids on human colon cancer cells. Cancer Letters, 110(1), 41-48.
 Landis‐Piwowar, K.R., Milacic, V., Dou, Q.P. (2008). Relationship between the methylation status of dietary flavonoids and their growth‐inhibitory and apoptosis‐inducing activities in human cancer cells.Journal of Cellular Biochemistry, 105(2), 514-523.
 Oršolić, N., et al. (2004). Immunomodulatory and antimetastatic action of propolis and related polyphenolic compounds.Journal of Ethnopharmacology, 94(2), 307-315.
 Zamin, L. L., et al. (2009). Resveratrol and quercetin cooperate to induce senescence‐like growth arrest in C6 rat glioma cells. Cancer Science, 100(9), 1655-1662.
 Trougakos, I.P., et al. (2003). Slowing down cellular aging in vitro. Modulating Aging and Longevity Kluwer Academic Publishers, 65-83.
 Chondrogianni, N., et al. (2010). Anti-ageing and rejuvenating effects of quercetin.Experimental Gerontology,45(10),763-771.
 Liu, J., Yu, H., Ning, X. (2006). Effect of quercetin on chronic enhancement of spatial learning and memory of mice.Science in China Series C:Life Sciences,49(6),583-590.
 Álvarez, P., et al. (2006). Improvement of leukocyte functions in prematurely aging mice after five weeks of diet supplementation with polyphenol-rich cereals. Nutrition, 22(9), 913-921.
 Nebus, J., Vassilatou, K., Philippou, L., Wallo, W. (2011). Clinical improvements in facial photoaged skin using a novel oak quercetin topical preparation.Journal of the American Academy of Dermatology, 64(2): AB73-AB73.
 Jung, M.K., Hur, D.Y., Song, S.B., Park, Y., Kim, T.S., Bang, S.I., … & Cho, D.H. (2010). Tannic acid and quercetin display a therapeutic effect in atopic dermatitis via suppression of angiogenesis and TARC expression in Nc/Nga mice. Journal of Investigative Dermatology, 130(5), 1459-1463.
 Weng, Z., Zhang, B., Asadi, S., Sismanopoulos, N., Butcher, A., Fu, X., … & Theoharides, T.C. (2012). Quercetin is more effective than cromolyn in blocking human mast cell cytokine release and inhibits contact dermatitis and photosensitivity in humans. PLoS One, 7(3), e33805.
 Karuppagounder, V., Arumugam, S., Thandavarayan, R.A., Sreedhar, R., Giridharan, V. V., & Watanabe, K. (2016). Molecular targets of quercetin with anti-inflammatory properties in atopic dermatitis. Drug discovery today, 21(4), 632-639.
 Escande, C., Nin,V., Price, N.L., Capellini, V., Gomes, A.P., Barbosa, M.T., … & Chini, E. N. (2013). Flavonoid Apigenin Is an Inhibitor of the NAD+ase CD38 Implications for Cellular NAD+Metabolism,Protein Acetylation, and Treatment of Metabolic Syndrome. Diabetes, 62(4), 1084-1093.
 Camacho-Pereira, J., Tarrago, M.G., Chini, C.C., Nin, V., Escande, C., Warner, G.M., … & Chini, E.N. (2016). CD38 dictates age-related NAD decline and mitochondrial dysfunction through an SIRT3-dependent mechanism. Cell metabolism, 23(6), 1127-1139.
 Schultz, M.B., & Sinclair, D.A. (2016). Why NAD+ Declines during Aging: It’s Destroyed. Cell metabolism,23(6),965-966.
 Coppé, J.P., Desprez, P.Y., Krtolica, A., & Campisi, J. (2010). The senescence-associated secretory phenotype: the dark side of tumor suppression. Annual review of pathology, 5, 99.
 López-Otín, C., Blasco, M.A., Partridge, L., Serrano, M., & Kroemer, G. (2013). The hallmarks of aging. Cell, 153(6), 1194-1217.
 van Deursen, J.M. (2014). The role of senescent cells in ageing. Nature, 509(7501), 439-446.
 Zhu, Y., Tchkonia, T., Pirtskhalava, T., Gower, A.C., Ding, H., Giorgadze, N., … & O’Hara, S.P. (2015). The Achilles’ heel of senescent cells: from transcriptome to senolytic drugs.Aging cell,14(4),644-658.
 Roos, C.M., Zhang, B., Palmer, A.K., Ogrodnik, M.B., Pirtskhalava, T., Thalji, N.M., … & Zhu, Y. (2016). Chronic senolytic treatment alleviates established vasomotor dysfunction in aged or atherosclerotic mice. Aging Cell, 15(5), 973-977.
 Edwards, R.L., Lyon, T., Litwin, S.E., Rabovsky, A., Symons,J.D., & Jalili, T. (2007). Quercetin reduces blood pressure in hypertensive subjects. The Journal of nutrition, 137(11), 2405-2411.
 Serban, M.C., Sahebkar, A., Zanchetti, A., Mikhailidis, D.P., Howard, G., Antal, D., … & Lip, G.Y. (2016). Effects of Quercetin on Blood Pressure: A Systematic Review and Meta‐Analysis of Randomized Controlled Trials. Journal of the American Heart Association, 5(7), e002713.