Enhanced Antioxidant Protection Against Heart Disease, Cancer, Allergies, and More
By Julius Goepp, MD
Quercetin’s ability to suppress cell proliferation, to promote programmed cell death, and to minimize DNA damage has made it of natural interest as a cancer-preventive nutrient as well,36,37 and epidemiologic studies strongly suggest that quercetin and other flavonoid intake is correlated with a reduced risk of certain cancers.38-43 Researchers have demonstrated quercetin’s ability to prevent or slow tumor development in experiments involving cancers of the brain, liver, colon, and other tissues.44-47
Clinical evidence of quercetin’s usefulness in cancer prevention and therapy is rapidly accumulating. An early Phase I clinical trial of quercetin in patients with various cancer types demonstrated a decrease in activity of enzymes required for tumor growth in nine of 11 patients studied.48 Two patients with advanced cancers that had failed to respond to standard chemotherapy experienced significant drops in chemical tumor markers during the study.
More recently, Cleveland Clinic oncologists investigated quercetin in patients who had familial adenomatous polyposis, an inherited condition producing hundreds of colonic polyps that ultimately turn to cancer.49 They combined the quercetin with curcumin, another nutrient with known anti-inflammatory and tumor-blocking potential, in five patients, treating and following them for six months. All patients had a reduction in both size (60%) and number of polyps (51%) over the course of treatment, with minimal adverse effects and no evidence of laboratory abnormalities. The researchers strongly encouraged larger controlled trials to further explore the supplements’ potential cancer-fighting abilities.
The diverse and multiple effects of quercetin on specific disease processes are overwhelming, and are certain to have an effect on longevity simply by reducing the impact of chronic illness. But there seems to be something else going on with this surprising polyphenol—something independent of its disease-preventing activity. Hard as it may be to believe, there is actually evidence that quercetin has a direct effect on prolonging life span, at least in simple laboratory organisms. For example, a Portuguese biochemistry research group has shown that, by increasing resistance to oxidative stress, quercetin supplements prolong the life span of laboratory yeast cells in culture by 60%!4
Biologists at Humboldt University in Berlin took these findings several steps further in their work on a simple roundworm C. elegans, demonstrating that feeding the tiny worms flavonoid-rich diets improved overall health and longevity.50 Digging deeper, the same group traced this powerful effect to the quercetin content of the supplement—they’ve even identified a set of four specific genes that seem to be activated by quercetin, pinpointing the precision with which this nutrient acts.50,51 Other scientists have found evidence that quercetin may mimic many beneficial biological effects of caloric restriction, which extends life span in animals and possibly in humans.5,52,53 The immediate impact on humans has also been shown by neuroscientists in Kentucky, who discovered that they could protect brain cells from the devastating effects of the toxic protein found in Alzheimer’s disease, beta-amyloid, by pre-treating the cells with quercetin, apparently through reduction in free radical damage caused by the deadly protein.54
Dosage and Safety
Health care practitioners recommend quercetin in doses ranging from 50 mg to 500 mg, one to three times daily.2,55
Quercetin is generally considered safe and well tolerated. Pregnant or nursing women should speak with a physician before using quercetin.2
Quercetin, a ubiquitous polyphenol found especially in apples, onions, and red grapes has been ignored for years while other members of its class took the limelight. In just the past two years, however, a virtual explosion of information has emerged about this versatile molecule. We now understand that it can fundamentally affect disease processes as different as obesity, cardiovascular disease, cancer, and asthma, through its powerful antioxidant effects that reduce inflammation throughout the body. Even more astonishingly, it is now clear that quercetin may have a direct and independent effect on prolonging life itself, through mechanisms that are becoming less mysterious as scientists focus their attention deep inside cellular processes.
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