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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.

Table 1.   Flavonoid Subclasses and Examples
Subclass Selected Examples
Flavones Apigenin, Chrysin, Luteolin
Flavonols Kaempferol, Myricetin, Quercetin
Flavanones Hesperidin, Naringenin
Flavanols (also called catechins) Epicatechin, Gallocatechin
Anthocyanidins Cyanidin, Malvidin, Pelargonidin
Anthocyanidins Cyanidin, Malvidin, Pelargonidin
Isoflanones Genistein, Daidzein

FROM:   Quercetin Monograph
Alternative Medicine Review 2011 (Jun); 16 (2): 172–194

Bioflavonoid Articles

What are Bioflavonoids?
A nice review by students from the University of North Carolina School of Pharmacy

Proanthocyanidin Power
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. [5] The flavonoids chrysin, baicalein, isorhamnetin, and several caffeic acid esters are also effective. [6]

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.


Bioflavonoid Research

Medicarpin and Millepurpan, Two Flavonoids Isolated from
Medicago sativa, Induce Apoptosis and Overcome
Multidrug Resistance in Leukemia P388 Cells

Phytomedicine. 2015 (Dec 1);   22 (13):   1186–1194

These data indicate that medicarpin and millepurpan possess pro-apoptotic properties and potentiate the cytotoxicity of chemotherapy drugs in multidrug resistant P388 leukemia cells by modulating P-gp-mediated efflux of drugs. These flavonoids may be used as chemopreventive agents or as sensitizer to enhance cytotoxicity of chemotherapy drugs in multidrug resistant cancer cells.

Neuroinflammatory Processes in Cognitive Disorders: Is There
a Role for Flavonoids and N-3 Polyunsaturated Fatty Acids
in Counteracting Their Detrimental Effects?

Neurochem Int. 2015 (Oct);   89:   63–74

We will also detail the current evidence indicating that flavonoids and n-3 polyunsaturated fatty acids are strong candidates in preventing neuroinflammation and modulating age-related memory decline, and we will describe the potential mechanisms of action underlying their neuroprotective effects. As such, these dietary bioactives represent important precursor molecules in the quest to develop a new generation of drugs capable of counteracting neuroinflammation and neurodegenerative diseases.

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.

Quercetin Monograph
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.

Cyclopamine and Quercetin Suppress the Growth of
Leukemia and Lymphoma Cells

Anticancer Res 2009 (Nov);   29 (11):   4629–4632

Cyclopamine and quercetin suppress the growth of a number of leukemia and lymphoma cells. This finding suggests the potential use of these compounds in molecularly-targeted therapy for leukemia and lymphoma.

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.

Flavonoids Apigenin and Quercetin Inhibit Melanoma Growth
and Metastatic Potential

Int J Cancer 2000 (Aug);   87 (4):   595–600

In conclusion, quercetin and apigenin inhibit melanoma growth and invasive and metastatic potential; therefore, they may constitute a valuable tool in the combination therapy of metastatic melanoma.

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.

Flavonoids Inhibit Cell Growth and Induce Apoptosis
in B16 Melanoma 4A5 Cells

Biosci Biotechnol Biochem 2000 (Sep);   64(9):   1813–20

We investigated the growth inhibitory activity of several flavonoids, including apigenin, luteolin, kaempherol, quercetin, butein, isoliquiritigenin, naringenin, genistein, and daizein against B16 mouse melanoma 4A5 cells.

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.

Monograph: Quercetin
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.

Antioxidant Flavonoids: Structure, Function and Clinical Usage
Alternative Medicine Review 1996 (Jul);   1 (2):   103–111 ~ FULL TEXT

Flavonoids have been shown to have anti-bacterial, anti-inflammatory, antiallergic, antimutagenic, antiviral, antineoplastic, anti-thrombotic, and vasodilatory activity.


Flavonoid Subclasses

The Quercetin Page
A Chiro.Org article collection
Discover the various ways that quercetin can support your health.

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