This section was compiled by Frank M. Painter, D.C. Send all comments or additions to:Frankp@chiro.org
If there are terms in these articles you don't understand, you can get a definition from the Merriam Webster Medical Dictionary. If you want information about a specific disease, you can access the Merck Manual. You can also search Pub Med for more abstracts on this, or any other health topic.
Flavonoids are found in most plant material. The most important dietary sources are fruits, tea and soybean. Green and black tea contains about 25% percent flavonoids. Flavonoids have powerful antioxidant properties, and are becoming very popular because they have many health promoting effects. Some of the activities attributed to flavonoids include: anti-allergic, anti-cancer, antioxidant, anti-inflammatory and anti-viral. The flavonoids quercetin is known for its ability to relieve hay fever, eszema, sinusitis and asthma, and for reducing the risk for cancer, and protection against osteoporosis. Consumption of red wine, red grape juice, grape skin and grape seeds has been linked to many health benefits. There are mainly two grape phytochemicals responsible for these benefits: proanthocyanidins and resveratrol. Proanthocyanidins are in the first place very strong antioxidants. Studies have shown that proanthocyanidins act as anti-cancer and anti-allergic agents, and that they improve heart health.
Nutrition Science News ~ June 2000
Pine bark and grape seed contain the flavonoids OPCs, which offer antioxidant protection against heart disease and cancer In the future, health care providers may hand out proanthocyanidin pills as readily as they recommend aspirin today. A steady stream of animal and in vitro studies supplemented by epidemiological evidence and a smattering of preliminary human studies reveal numerous health benefits associated with these compounds. Chief among the benefits is antioxidant protection against heart disease and cancer.
Nutrition Science News ~ December 2001
Eaten in large amounts by primitive humans, anthocyanins are antioxidant flavonoids that protect many body systems. They have some of the strongest physiological effects of any plant compounds, and they are also things of beauty: anthocyanins provide pigment for pansies, petunias, and plums. (Anthocyanins are a separate class of flavonoids from proanthocyanidins, discussed in NSN 2000; 5 (6): 231–234)
Quercetin: A Natural Reverse Transcriptase Inhibitor
Nutrition Science News ~ March 1997
Along with synthetic protease inhibitors, drug companies are using synthetic reverse transcriptase inhibitor drugs to combat AIDS. On one hand, the possibility exists that natural protease inhibitors could help combat HIV the same way they help to prevent cancer; by the same token, it is possible that natural reverse transcriptase inhibitors could do the same.
Ease Gout Pain
Nutrition Science News ~ July 1999
A swollen big toe and a hobbled gait—finally, excruciating pain sends your customer to fill a prescription for allopurinol, the standard drug for treating gout. Are there natural remedies you can recommend to ease his suffering in addition to or instead of the pharmaceutical? YES! The enzyme xanthine oxidase catalyzes the last step in the conversion of purines to uric acid. Allopurinol, the medication prescribed for gout prevention, is a xanthine oxidase inhibitor. In vitro, xanthine oxidase is inhibited by the flavonoids luteolin and apigenin nearly as well as it is by allopurinol.  The flavonoids chrysin, baicalein, isorhamnetin, and several caffeic acid esters are also effective. 
Quercetin Is Promising for Chronic Prostatitis
Nutrition Science News ~ April 2001
Quercetin, a naturally occurring bioflavonoid found in apples, black tea, and onions, was tested as a treatment for chronic prostatitis in a nonblinded study by researchers at the Institute for Male Urology in Encino, Calif. In the trial, an encouraging 59 percent of the subjects improved.1 In light of these results, Daniel Shoskes, M.D., and Jacob Rajfer, M.D., from the Division of Urology, Harbor UCLA Medical Center in Los Angeles, decided to do a proper double-blind test of quercetin vs. placebo.
Flavonoid-based Therapies in the Early Management
of Neurodegenerative Diseases
Adv Nutr. 2015 (Jan 15); 6 (1): 64–72
During the past several years, there has been enormous progress in the understanding of the causative factors that initiate neuronal damage in various neurodegenerative diseases, including Alzheimer disease, Parkinson disease, multiple sclerosis, amyotrophic lateral sclerosis, and Huntington disease. Preventing neuronal damage and neuronal death will have a huge clinical benefit. Regular consumption of flavonoids has been associated with a reduced risk of neurodegenerative diseases. In addition to their antioxidant properties, these polyphenolic compounds exhibit neuroprotective properties by their interaction with cellular signaling pathways followed by transcription and translation that mediate cell function under both normal and pathologic conditions. This review focuses on human intervention studies as well as animal studies on the role of various flavonoids in the prevention of neurodegenerative diseases.
Alternative Medicine Review 2011 (Jun); 16 (2): 172–194 ~ FULL TEXT
Quercetin is categorized as a flavonol, one of the six subclasses of flavonoid compounds (Table 1). Flavonoids are a family of plant compounds that share a similar flavone backbone (a three-ringed molecule with hydroxyl [OH] groups attached). A multitude of other substitutions can occur, giving rise to the subclasses of flavonoids and the different compounds found within these subclasses. Flavonoids also occur as either glycosides (with attached sugars [glycosyl groups]) or as aglycones (without attached sugars)
Effect of Cocoa Products on Blood Pressure:
Systematic Review and Meta-analysis
American Journal of Hypertension 2010 (Jan); 23 (1): 97–103
The evidence supporting the antihypertensive effects of cocoa has been building over the last few years, and this systematic review and meta-analysis of 10 randomized controlled trials, comprising 297 individuals confirms the BP-lowering capacity of flavanol-rich cocoa products. The high level of flavanols found in the cocoa plant is believed to be responsible for the lowering of blood pressure.
Flavonoids: Recent Advances as Anticancer Drugs
Recent Pat Anticancer Drug Discov 2010 (Jun); 5 (2): 152–164
Flavonoids belong to polyphenolic secondary metabolites with broad-spectrum pharmacological activities and extensive biological effects, and the most prominent activity is their potential role as anticancer agents. In recent years, flavonoids and their synthetic analogues have been intensely investigated in the treatment of ovarian, breast, cervical, pancreatic, and prostate cancer.
Effects of Daily Oral Administration of Quercetin Chalcone and
Modified Citrus Pectin on Implanted Colon-25 Tumor Growth
in Balb-c Mice
Alternative Medicine Review 2000 (Dec); 5 (6): 546–552 ~ FULL TEXT
Previous research has confirmed that quercetin exhibits antitumor properties, likely due to immune stimulation, free radical scavenging, alteration of the mitotic cycle in tumor cells, gene expression modification, anti-angiogenesis activity, or apoptosis induction, or a combination of these effects. MCP has inhibited metastases in animal studies of prostate cancer and melanoma. To date, no study has demonstrated a reduction in solid tumor growth with MCP, and there is no research into the antitumor effect of QC. This study examines the effects of MCP and QC on the size and weight of colon-25 tumors implanted in balb-c mice.
Antioxidants and Cancer III: Quercetin
Alternative Medicine Review 2000 (Jun); 5 (3): 196–208 ~ FULL TEXT
Quercetin is a flavonoid molecule ubiquitous in nature. A number of its actions make it a potential anti-cancer agent, including cell cycle regulation, interaction with type II estrogen binding sites, and tyrosine kinase inhibition. Quercetin appears to be associated with little toxicity when administered orally or intravenously. Much in vitro and some preliminary animal and human data indicate quercetin inhibits tumor growth. More research is needed to elucidate the absorption of oral doses and the magnitude of the anti-cancer effect.
Oligomeric Proanthocyanidin Complexes: History, Structure,
and Phytopharmaceutical Applications
Alternative Medicine Review 2000 (Apr); 5 (2): 144–151 ~ FULL TEXT
Considerable recent research has explored therapeutic applications of oligomeric proanthocyanidin complexes (OPCs), naturally occurring plant metabolites widely available in fruits, vegetables, nuts, seeds, flowers, and bark. OPCs are primarily known for their antioxidant activity. However, these compounds have also been reported to demonstrate antibacterial, antiviral, anticarcinogenic, anti-inflammatory, anti-allergic, and vasodilatory actions. In addition, they have been found to inhibit lipid peroxidation, platelet aggregation, capillary permeability and fragility, and to affect enzyme systems including phospholipase A2, cyclooxygenase, and lipoxygenase.
Quercetin: A Review of Clinical Applications
Natural Medicine Online July 2000
Quercetin is frequently used therapeutically in allergic conditions, including asthma and hayfever, eczema, and hives. Additional clinical uses include treatment of gout, pancreatitis and prostatitis, which are also, in part, inflammatory conditions. The common link is its ability to mediate production and manufacture of pro-inflammatory compounds.
Alternative Medicine Review 1998 (Apr); 3 (2): 140–143 ~ FULL TEXT
Quercetin appears to have many beneficial effects on human health, including cardiovascular protection, anti-cancer activity, anti-ulcer effects, anti-allergy activity, cataract prevention, antiviral activity, and anti-inflammatory effects.