Quercetin exerts many beneficial health effects, including improvement of cardiovascular health, reducing risk for cancer, protection against osteoporosis. This phytochemical has anti-inflammatory, anti-allergic and antitoxic effects. Most of these properties are linked to its strong antioxidant action of quercetin but quercetin also modulates the expression of specific enzymes. Quercetin induces apoptosis and influences protein and lipid kinase signaling pathways. Quercetin is a candidate for preventing obesity-related diseases.
Quercetin may help to reduce symptoms of diabetes patients. One study showed that quercetin reduced blood glucose level and improved improved plasma insulin levels in streptozotocin-induced diabetic rats. An in-vitro study concluded that quercetin may have a pharmacological application in treating cardiovascular disease in diabetes mellitus patients.
Quercetin shows anti-inflammatory action by its direct antioxidant action and inhibition of inflammatory mediators and enzymes, such as lipoxygenase. Quercetin also inhibits the release of histamine, which causes congestion, by basophils and mast cells. Studies have shown an improved lung function and lower risk of certain respiratory diseases (asthma and bronchitis) for people with high apple (rich in quercetin) intake. Patients with increased levels of inflammation and oxidative stress might benefit most from a quercetin supplementation.
To investigate the effects of quercetin supplementation on incidence of upper respiratory tract infections and exercise-induced changes in immune function. Trained male cyclists were randomized to quercetin or placebo groups and, under double-blind procedures, received 3 weeks quercetin (1000 mg a day) or placebo before, during, and for 2 weeks after a 3-d period in which subjects cycled for 3 hours a day at approximately 57% Wmax. Quercetin versus placebo ingestion did not alter exercise-induced changes in several measures of immune function, but it significantly reduced upper respiratory tract infection incidence in cyclists during the 2-wk period after intensified exercise.
Studies demonstrate that flavonoid-rich diets protect against myocardial infarction and stroke. As many other flavonoids, quercetin inhibits oxidation of LDL (bad) cholesterol, lowers blood pressure and reduces the risk of heart disease.
Studies have shown that quercetin reduces cancer risk of prostate, ovary, breast, gastric and colon cells. Numerous in-vitro studies show that quercetin induces apoptosis of cancer cells through different mechanisms.
Preliminary studies indicate that quercetin my inhibit the proliferation of androgen- independent human prostatic tumor cells. In rats, in combination with finasteride, it reduces prostate weight. Whether therapy alone benefits those with benign prostate hyperplasia is not clearly known at this time. Many flavonoids act as aromatase inhibitors.
Quercetin supplementation has been linked with improved performance, but supporting evidence is week and often conflicting. Scientists suggest that quercetin may aid performance through its anti-inflammatory properties or by stimulating the activity of mitochondria.
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