Quercetin is a plant pigment (flavonoid), which may have many health benefits. Quercetin is also a natural antioxidant
found mainly in red wine grapefruit, onions, apples, black tea and Proustia pyrifolia [30]. In studies, quercetin protected
cells in the body from damage by free radicals, [12-14] . Quercetin is said to benefit people suffered from high
cholesterol, diabetes, cataracts, peptic ulcer, inflammation, chronic fatigue syndrome, heart attacks and even strokes,
quercetin may further benefit people suffered from allergies such as hay fever, hives, eczema and asthma. In next
section, we are going to overview what evidence found to support these health benefit claims.

Quercetin benefits on performance
Researchers found that quercetin intake led to changes in mitochondrial capacity in an animal study. These changes
in mitochondrial capacity were associated with an increase in both maximal endurance capacity and voluntary wheel
running activity. These quercetin benefits on fitness without exercise training may have important implications for
enhancement of athletic and military performance and may also extend to prevention and treatment of chronic
diseases. [A1]

Quercetin benefits against allergy, inflammnation and infection
Asthma incidence was lower at high quercetin intakes. [28] Quercetin may address the inflammatory component of
asthma. Quercetin prevents certain immune cells from releasing histamine. Histamine is a chemical that triggers an
allergic reaction. [1-4]  One study shows quercetin might help prostatitis, an inflammation or infection of the prostate
gland. [5], while another study shows quercetin supplementation reduced symptoms of interstitial cystitis [6] Quercetin
even seems to be able to prevent certain viruses from infecting cells from cell studies. [22-23]

Quercetin benefits on heart diseases, stroke and aggregation
Quercetin might help prevent heart diseases and stroke. [7-10] Quercetin has inhibitory properties of blood platelet
aggregation (clumping). [11]

Quercetin has been said to have benefits on people suffered from cancers, it may also lower the risk of certain
cancers. [15-19]

Cell metastasis is a major cause of death from cancer and can arise from excessive levels of oxidative stress.
Quercetin inhibits cell motility via the inhibition of matrix metalloproteinase activation in human fibrosarcoma cells. [B1]

Breast Cancer Cells
Wnt/β-catenin signaling pathway has been implicated in mammary tumorigenesis, where its abnormal activation is
associated with the development of breast cancer, Quercetin is found to be able to downregulate the Wnt/β-catenin
signaling activity. [B2] Topotecan has cytotoxic activity against certain breast cancer cells. Quercetin was found to
increase the efficacy of Topotecan in the treatment of breast cancers. [31] Another study shows quercetin combined
with 1,2,3,4,6-penta-O-galloyl-β-D-glucose induced S-phase arrest and apoptosis in MDA-BM-231 human breast
cancer cells through downregulation of S-phase kinase protein 2 expression. [B5]

Lung Cancer Cells
Quercetin inhibited growth by suppressing NF-κB and by increasing the expression of death receptors and cell cycle
inhibitors in non-small cell lung cancer (NSCLC) cells. [B6

Ovarian Cancer Cells
PEGylated liposomal quercetin have been inhibited cell proliferation, induced apoptosis, and induced cell cycle arrest
in human ovarian cancer cells. [B3]

Neuroblastoma is a neuroendocrine tumour derived from neural crest cells.Quercetin showed a promising effect on
neuroblastoma in a vitro study. [B4]

Prostate Cancer

Quercetin benefits on cancer, diabetes and cataracts.
A trend toward a reduction in risk of type 2 diabetes is associated with higher quercetin intake. [20] Further, quercetin
might protect rodents with diabetes from forming cataracts. [21]

Quercetin bromelain
Bromelain is an enzyme complex derived from the pineapple stem. Bromelain may assist the absorption of quercetin in
the G.I. tract. [25] Consequently there are two popular quercetin products - "quercetin bromelain" and activated

Quercetin and bromelain both have inhibitory properties of blood platelet aggregation (clumping). Consequently,
manufacturers are interesting to put them together in the product. [25-26]

ACTIVATED QUERCETIN Source Naturals Activated Quercetin is probably the most advertised quercetin product over
the internet. It is a blend of quercetin, magnesium ascorbate, and bromelain.

Activated Quercetin is actually a state-of-the-art quercetin complex. It is advertised that the additional ingredients can
maximize the absorption and benefits of quercetin. Thus, quercetin is thought to be a potent formula.

Quecetin Side Effects
Most supplements have benefits and side effects. However, the severity and type of side effects vary from users to
Dr. Ray Sahelian says, "Quercetin side effects have not been reported in the medical literature... Quercetin side
effects with long term supplementation... is not known" (September 10, 2011).

According to
Webmd.com, quercetin is probably safe up to dosage of 500 mg twice daily for 12 weeks. The quecetin
side effects may include headache and tingling of the arms and legs. Very high doses might cause kidney damage.
(September 10, 2011) While
Sloan-Kettrering says, "No adverse effects have been reported with single oral doses up
to 4 grams." Papain and bromelain may support the absorption of quercetin in the intestine.

Drug interaction was also found with quercetin products. Quercetin raises the bioavailability of ditiazem significantly.

[1] Ogasawara H et al, Effect of selected flavonoids on histamine release (HR) and hydrogen peroxide (H2O2) generation by human
leukocytes [abstract]. J Allergy Clin Immunol. 1985;75(suppl):184. [2] Middleton E Jr. Effect of flavonoids on basophil histamine release
and other secretory systems. Prog Clin Biol Res. 1986;213:493–506.] [3] Knekt P et al, Flavonoid intake and risk of chronic diseases. Am
J Clin Nutr. 2002 Sep;76(3):560-8.]  [4] Miller AL. The etiologies, pathophysiology, and alternative/complementary treatment of asthma.
Altern Med Rev. 2001 Feb;6(1):20-47. [5] Shoskes DA et al. Quercetin in men with category III chronic prostatitis: a preliminary prospective,
double-blind, placebo-controlled trial. Urology. 1999;54:960–963.][6] Rodriguez LV et al. Treatment of interstitial cystitis with a quercetin
containing compound: a preliminary, double-blind placebo control trial. Presented at: American Urological Association 2001 Annual
Meeting; June 2–7, 2001; Anaheim, Calif][7] Constant J. Alcohol, ischemic heart disease, and the French paradox. Coron Artery Dis.
1997;8:645–649. [8] Hayek T et al, Reduced progression of atherosclerosis in apolipoprotein E-deficient mice following consumption of
red wine, or its polyphenols quercetin or catechin, is associated with reduced susceptibility of LDL to oxidation and aggregation.
Arterioscler Thromb Vasc Biol. 1997;17:2744–2752. [9] Frankel EN et al Inhibition of human LDL oxidation by resveratrol. Lancet. 1993;
341:1103–1104. Alliangana DM. Effects of beta-carotene, flavonoid quercetin and quinacrine on cell proliferation and lipid peroxidation
breakdown products in BHK-21 cells. East Afr MedJ. 1996;73:752–757. [10] Keli SO et al. Dietary flavonoids, antioxidant vitamins, and
incidence of stroke: the Zupthen study. Arch Intern Med. 1996;156:637–642. [11] [Beretz, et al, “Role of cyclic AMP in the inhibition of
human platelet aggregation by quercetin, a flavonoid that potentiates the effect of prostacyclin.” Biochemical Pharmacology 1981;31(22):
3597-600.[12] Quercetin protects LDL from oxidation by lipid peroxides and transition metal ions. Oxidized LDL is absorbed by
macrophages and arterial endothelial cells, eventually leading to plaque deposits in arterial walls. [13] Afanas’ev, I.B. et. al., “Chelating
and free radical scavenging mechanisms of inhibitory action of rutin and quercetin in lipid peroxidation.” Biochemical Pharmacology
1989;38(11):1763-69. [14] De Whalley, C.V., “Flavonoids inhibit the oxidative modification of low density lipoproteins by macrophages.”
Biochemical Pharmacology 39(11):1743-50.][15] Balasubramanian S, Govindasamy S. Inhibitory effect of dietary flavonol quercetin on
7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch carcinogenesis. Carcinogenesis. 1996;17:877–879. [16] Cross HJ et
al. Effect of quercetin on the genotoxic potential of cisplatin. Int J Cancer. 1996;66:404–408. [17] Hoffman R et al. Enhanced anti-
proliferative action of busulphan by quercetin on the human leukaemia cell line K562. Br J Cancer. 1989;59:347–348. [18] ElAttar TM et
al. Modulating effect of resveratrol and quercetin on oral cancer cell growth and proliferation. Anticancer Drugs. 1999;10:187–193. [19]
Yoshida M et al. Quercetin arrests human leukemic T-cells in late G1 phase of the cell cycle. Cancer Res. 1992;52:6676–6681. [20]
Knekt P., Flavonoid intake and risk of chronic diseases. Am J Clin Nutr. 2002 Sep;76(3):560-8.] [21] Varma SD et al. Diabetic cataracts
and flavonoids. Science. 1977;195:205–206] [22] Kaul TN et al. Antiviral effect of flavonoids on human viruses. J Med Virol. 1985;15:71–
79. [23] Musci I, Pragai BM. Inhibition of virus multiplication and alteration of cyclic AMP level in cell cultures by flavonoids. Experientia.
1985;41:930–931.] [24] Choi JS. Enhanced diltiazem bioavailability after oral administration of diltiazem with quercetin to rabbits. Int J
Pharm. 2005 Jun 13;297(1-2):1-8. [25] Hollma, P. et. al., “Absorption of dietary quercetin glycosides and quercetin in healthy ileostomy
volunteers.” Am. J. Clin. Nutr. 1995;62:1276-82.][25] Beretz, et al, “Role of cyclic AMP in the inhibition of human platelet aggregation by
quercetin, a flavonoid that potentiates the effect
of prostacyclin.” Biochemical Pharmacology 1981;31(22):3597-600. [26] Heinicke et al “Effect of bromelain (Ananase®) on human
platelet aggregation. ”Experientia 1972;28(7):844] [27] Ebeler SE et al, Animal models and analytical approaches for understanding the
relationships between wine and cancer. Drugs Exp Clin Res. 2005;31(1):19-27.[30] Delporte C, Analgesic-antiinflammatory properties of
Proustia pyrifolia. J Ethnopharmacol. 2005 May 13;99(1):119-24.[31] Akbas SH et al, The effect of quercetin on topotecan cytotoxicity in
MCF-7 and MDA-MB 231 human breast cancer cells. J Surg Res. 2005 May 1;125(1):49-55. [A1] Davis JM, Murphy EA, Carmichael MD,
Davis B. Quercetin increases brain and muscle mitochondrial biogenesis and exercise tolerance.Am J Physiol Regul Integr Comp
Physiol. 2009 Feb 11. [B1] Lee DE et al, Quercetin Suppresses Intracellular ROS Formation, MMP Activation, and Cell Motility in Human
Fibrosarcoma Cells. J Food Sci. 2013 Jul 31. [B2] Kim H, et al, Regulation of Wnt signaling activity for growth suppression induced by
quercetin in 4T1 murine mammary cancer cells. Int J Oncol. 2013 Oct;43(4):1319-25 [B3] Long Q, et al, Induction of apoptosis and
inhibition of angiogenesis by PEGylated liposomal quercetin in both cisplatin-sensitive and cisplatin-resistant ovarian cancers. J Biomed
Nanotechnol. 2013 Jun;9(6):965-75. [B4] Sugantha Priya E et al, Anti-cancer activity of quercetin in neuroblastoma: an in vitro approach.
Neurol Sci. 2013 Jun 16 [B5] Huang C et al, Co-treatment with quercetin and 1,2,3,4,6-penta-O-galloyl-β-D-glucose causes cell cycle
arrest and apoptosis in human breast cancer MDA-MB-231 and AU565 cells. J Agric Food Chem. 2013 Jul 3;61(26):6430-45 [B6] Youn H,
et al, Quercetin potentiates apoptosis by inhibiting nuclear factor-kappaB signaling in H460 lung cancer cells. Biol Pharm Bull. 2013;36(6):
Quercetin side effects, quercetin benefits, quercetin bromelain
August 28, 2013 Zhion@zhion.com
quercetin side effects, quercetin benefits
This article discusses the benefits and side effects of quercetin. Different people may experience different side
effects and benefits of quercetin. You are encouraged to report adverse side effects to FDA, and its website is

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