Quercetin and isoquercetin have a host of potential health benefits and it has been used by various cultures in traditional medicine for centuries. Today we are going to take a look at some of the more significant health benefits.
Polyphenols like quercetin as part of a health regimen have the may have the potential to help keep us healthy as we grow older and more able to enjoy an independent active life.
For a healthy brain
Quercetin and isoquercetin are both powerful antioxidants that may protect the brain from the damaging effects of oxidative stress by free radical scavenging (1). Neuroleptics, used for treating schizophrenia and other similar disorders, are often associated with side effects involving movement disorders, similar to Parkinson’s. Pretreatment with Quercetin reduced the side effects of neuroleptic medications in mice and may be beneficial as a therapy to reduce the unpleasant side effects of neuroleptic drugs.
Studies have also shown quercetin can protect the brain from the toxicity associated with the D-galactose (2). Quercetin can protect from this toxicity by increasing superoxide dismutase (a natural antioxidant enzyme) levels and reducing malondialdehyde (a biomarker of oxidative stress).
Research has shown quercetin can inhibit the proinflammatory signals associated with various neurodegenerative conditions such as Alzheimer’s disease, meningitis, AIDS dementia complex and also stroke (3). The results also showed that chronic treatment with flavonoids reversed the cognitive deficits of aging and LPS-intoxication in mice. This suggests that quercetin may be important in the prevention of memory deficits, one of the symptoms related to Alzheimer’s.
Quercetin was shown to improve the exploratory behaviour, spatial awareness and memory of aged mice (4). The flavonoid was able to enhance brain function, reduce oxidative stress by increasing glutathione antioxidant levels. This suggests that quercetin exerts an influence over brain aging and the associated cognitive decline.
More than just a gut feeling
Chronic stress levels can lead to mast cells in the gut becoming unstable, a process that causes an increase of permeability of the gut wall or so called leaky gut syndrome (5-6).
Flavonoids including quercetin have been shown to tighten the junctions between the mast cells thus reducing gut permeability in rodent studies (7). So quercetin might be beneficial in dealing with leaky gut syndrome resulting from chronic stress.
Quercetin is antibacterial
Quercetin has been shown to have an antibacterial effect against a number of Staphylococcus infections, including the antibiotic resistant S. aureus (MRSA) bacteria (8). Another study also showed that quercetin weakens the MRSA bacteria making it vulnerable to other antibacterial agents and can also combat H. Pylori (9-10).
A study also showed that quercetin has potential for the treatment of dental cavities and gum infections due to it being able to prevent the growth of a wide range of oral bacteria (11).
May help weight control
In a mouse study quercetin was able to reduce body weight by almost 40% and helped to suppress the expression of fat cell metabolism and inflammatory cytokines (12).
One of the ways quercetin helps regulate weight is by modulation of the AMPK and MAPK pathways (13). AMP-activated protein kinase (AMPK) plays is a master regulator of cellular energy homeostasis. Mitogen-activated protein kinases (MAPKs) is an evolutionary conserved family of serine/threonine protein kinases involved in a range of fundamental cellular processes such as proliferation, differentiation, motility, stress response, apoptosis, and survival. Quercetin is able to block the formation of fat cells and cause existing fat cells to destroy themselves.
Another mouse study showed that dietary quercetin reduced excess body weight caused by a high fat diet and improved insulin sensitivity as well as glucose intolerance (14). A further study showed quercetin was able to inhibit the accumulation of fat cells and block obesity-induced inflammation (15). And in a rat study using obese animals high doses of quercetin were able to reduce blood glucose levels, improve blood lipid profile and reduced high blood pressure (16).
Quercetin might help with Diabetes
In a study where mice were given a quercetin enriched diet for seven weeks, researchers showed a reduction of blood glucose and blood glycated hemoglobin (17). These changes also did not adversely affect insulin production.
A study of rats with type 1 diabetes who were given quercetin at a dose of 10-15 mg/kg for 10 days also showed significantly lower blood sugar levels (18).
Quercetin has an inhibitory effect on the uptake of glucose due to its influence on the glucose transporter GLUT4 (19). GLUT4 is an Insulin-regulated facilitative glucose transporter that transports glucose and plays a key role in metabolism.
The ERK 1/2 pathway is also a target for quercetin. This pathway plays an important role in regulating glucose-induced insulin production (20). Quercetin increases insulin secretion and protects pancreatic β-cells against oxidative damage via the ERK1/2 pathway.
Quercetin is also known to inhibit the NF-kb protein complex, this is a master regulator of inflammatory response and plays a key role in the immune system. However over activation of NF-kb results in excessive immune response, chronic inflammation and tissue damage. Quercetin is able to reduce the level of NF-kb thus modulating the inflammatory response often seen in diabetic subject (21).
May relieve the symptoms of arthritis
An in vitro study discovered that quercetin is able to inhibit both neutrophil and synoviocyte proliferation (22). Neutrophils are the most common type of granulocytes and are the most abundant type of white blood cells in most mammals. Neutrophil and synoviocyte proliferation are both important factors in the development of arthritis to quercetin being able to influence them could be useful in treating arthritis.
This makes sense as quercetin is known to inhibit MMP-9 and TNF-a. MMP-9 is one of a class of zinc-dependent enzymes called the Matrix metalloproteinases (MMPs), which are involved in the body’s natural process of tissue repair and replacement. Tumor Necrosis Factor (TNF) is an inflammatory cytokine involved in the immune response, excessive levels of which cause chronic inflammation and contributes to aging and disease progression. Quercetin taken at a dose of 750mg a day was able to ease arthritic pain and the associated inflammation (23).
And finally quercetin does not have the toxicity that drugs such as methotrexate and paclitaxel have which are often used to treat arthritis (24).
There are a myriad of health benefits from quercetin, isoquercetin and related flavonoids and these are only a small selection of them. With its beneficial effects and lack of adverse side effects it is worth considering making this supplement a regular part of your health regimen.
(1) Naidu, P. S., & Kulkarni, S. K. (2004). Quercetin, a bioflavonoid, reverses haloperidol-induced catalepsy. Methods and findings in experimental and clinical pharmacology, 26(5), 323-326.
(2) Avigad, G., Amaral, D., Asensio, C., & Horecker, B. L. (1962). The D-galactose oxidase of Polyporus circinatus. Journal of Biological Chemistry, 237(9), 2736-2743.
(3) Patil, C. S., Singh, V. P., Satyanarayan, P. S. V., Jain, N. K., Singh, A., & Kulkarni, S. K. (2003). Protective effect of flavonoids against aging-and lipopolysaccharide-induced cognitive impairment in mice. Pharmacology, 69(2), 59-67.
(4) 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.
(5) Pearce, F. L., Befus, A. D., & Bienenstock, J. (1984). Mucosal mast cells: III. Effect of quercetin and other flavonoids on antigen-induced histamine secretion from rat intestinal mast cells. Journal of Allergy and Clinical Immunology, 73(6), 819-823.
(6) Santos, J., Benjamin, M., Yang, P. C., Prior, T., & Perdue, M. H. (2000). Chronic stress impairs rat growth and jejunal epithelial barrier function: role of mast cells. American Journal of Physiology-Gastrointestinal and Liver Physiology, 278(6), G847-G854.
(7) Suzuki, T., & Hara, H. (2011). Role of flavonoids in intestinal tight junction regulation. The Journal of nutritional biochemistry, 22(5), 401-408.
(8) Hirai, I., Okuno, M., Katsuma, R., Arita, N., Tachibana, M., & Yamamoto, Y. (2010). Characterisation of anti‐Staphylococcus aureus activity of quercetin. International journal of food science & technology, 45(6), 1250-1254.
(9) Hirai, I., Okuno, M., Katsuma, R., Arita, N., Tachibana, M., & Yamamoto, Y. (2010). Characterisation of anti‐Staphylococcus aureus activity of quercetin. International journal of food science & technology, 45(6), 1250-1254.
(10) Ramos, F. A., Takaishi, Y., Shirotori, M., Kawaguchi, Y., Tsuchiya, K., Shibata, H., … & Takeuchi, M. (2006). Antibacterial and antioxidant activities of quercetin oxidation products from yellow onion (Allium cepa) skin. Journal of agricultural and food chemistry, 54(10), 3551-3557.
(11) Shu, Y., Liu, Y., Li, L., Feng, J., Lou, B., Zhou, X., & Wu, H. (2011). Antibacterial activity of quercetin on oral infectious pathogens. African Journal of Microbiology Research, 5(30), 5358-5361.
(12) Seo, M. J., Lee, Y. J., Hwang, J. H., Kim, K. J., & Lee, B. Y. (2015). The inhibitory effects of quercetin on obesity and obesity-induced inflammation by regulation of MAPK signaling. The Journal of nutritional biochemistry, 26(11), 1308-1316.
(13) Ahn, J., Lee, H., Kim, S., Park, J., & Ha, T. (2008). The anti-obesity effect of quercetin is mediated by the AMPK and MAPK signaling pathways. Biochemical and biophysical research communications, 373(4), 545-549.
(14) Dong, J., Zhang, X., Zhang, L., Bian, H. X., Xu, N., Bao, B., & Liu, J. (2014). Quercetin reduces obesity-associated ATM infiltration and inflammation in mice: a mechanism including AMPKα1/SIRT1. Journal of lipid research, 55(3), 363-374.
(15) Seo, M. J., Lee, Y. J., Hwang, J. H., Kim, K. J., & Lee, B. Y. (2015). The inhibitory effects of quercetin on obesity and obesity-induced inflammation by regulation of MAPK signaling. The Journal of nutritional biochemistry, 26(11), 1308-1316.
(16) Rivera, L., Morón, R., Sánchez, M., Zarzuelo, A., & Galisteo, M. (2008). Quercetin ameliorates metabolic syndrome and improves the inflammatory status in obese Zucker rats. Obesity, 16(9), 2081-2087.
(17) Kim, J. H., Kang, M. J., Choi, H. N., Jeong, S. M., Lee, Y. M., & Kim, J. I. (2011). Quercetin attenuates fasting and postprandial hyperglycemia in animal models of diabetes mellitus. Nutrition research and practice, 5(2), 107-111.
(18) Torres-Piedra, M., Ortiz-Andrade, R., Villalobos-Molina, R., Singh, N., Medina-Franco, J. L., Webster, S. P., … & Estrada-Soto, S. (2010). A comparative study of flavonoid analogues on streptozotocin–nicotinamide induced diabetic rats: Quercetin as a potential antidiabetic agent acting via 11β-Hydroxysteroid dehydrogenase type 1 inhibition. European journal of medicinal chemistry, 45(6), 2606-2612.
(19) Strobel, P., Allard, C., Perez-Acle, T., Calderon, R., Aldunate, R., & Leighton, F. (2005). Myricetin, quercetin and catechin-gallate inhibit glucose uptake in isolated rat adipocytes. Biochemical Journal, 386(3), 471-478.
(20) Youl, E., Bardy, G., Magous, R., Cros, G., Sejalon, F., Virsolvy, A., … & Bataille, D. (2010). Quercetin potentiates insulin secretion and protects INS‐1 pancreatic β‐cells against oxidative damage via the ERK1/2 pathway. British journal of pharmacology, 161(4), 799-814.
(21) Dias, A. S., Porawski, M., Alonso, M., Marroni, N., Collado, P. S., & González-Gallego, J. (2005). Quercetin decreases oxidative stress, NF-κB activation, and iNOS overexpression in liver of streptozotocin-induced diabetic rats. The Journal of nutrition, 135(10), 2299-2304.
(22) Jackson, J. K., Higo, T., Hunter, W. L., & Burt, H. M. (2006). The antioxidants curcumin and quercetin inhibit inflammatory processes associated with arthritis. Inflammation Research, 55(4), 168-175.
(23) Harrison, A. P., & Cooper, R. G. (2008). Quercetin: health benefits with relevance to TNF-alpha-linked inflammatory diseases. Journal of Pre-Clinical and Clinical Research, 2(2).
(24) O’Dell, J. R. (1997). Methotrexate use in rheumatoid arthritis. Rheumatic Disease Clinics of North America, 23(4), 779-796.