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.
Polyphenols are a category of chemicals that naturally occur in plants. There are more than 500 unique polyphenols. Collectively, these chemicals are known as phytochemicals.
Polyphenols are secondary metabolites (also known as Phytoalexins) of plants and are generally involved in defense against ultraviolet radiation or aggression by pathogens. In the last decade, there has been much interest in the potential health benefits of dietary plant polyphenols as antioxidant. Epidemiological studies and associated meta-analyses strongly suggest that long term consumption of diets rich in plant polyphenols offer protection against development of cancers, cardiovascular diseases, diabetes, osteoporosis and neurodegenerative diseases. 
Polyphenols can be further categorized into the following groups:
Updates in Neurology: The Neuroprotective Role of Dietary Polyphenols
Restorative Medicine Digest; 2021 (Feb 11)
Polyphenols are a group of naturally occurring bioactive compounds found in high amounts in many fruits, vegetables, seeds, nuts, herbs, and spices. It’s been known for a while that polyphenols are important antioxidants. For example, the dopamine-preserving effect of catechin-rich polyphenol extracts from green tea observed in animal models of Parkinson’s disease, is thought to be due in part to the ability of polyphenols to modulate the antioxidant activity of superoxide dismutase.  Now, an increasing number of studies suggest that dietary polyphenols have potent anti-inflammatory and neuroprotective properties as well. In particular, studies report that polyphenols protect neurons from neurotoxins; modulate neuroinflammation; and improve memory, learning, and cognitive function. The traditional Mediterranean diet is very rich in polyphenol-containing plant foods, which is one reason it’s thought to offer protection against neurodegeneration and cognitive decline.
Are Organics Really Healthier?
Functional Foods & Nutraceuticals (Mar 2003)
But the most exciting nutritional differences may be in phytonutrients — the five to 10,000 compounds in plants other than vitamins and minerals, often with known antioxidant effects on human health.  Many believe they are the primary reason fruits and vegetables are so health-promoting. They may be higher in organic foods primarily because many phytonutrients are part of the plant's defence systems and the lack of pesticide usage forces the plant to produce more of its own defences in the absence of an artificial one. Research is in its infancy, though higher levels in organic foods have been found for lycopene in tomatoes,  polyphenols in potatoes,  flavonols in apples  and resveratrol in red wine. 
Phytochemicals: Nutrients Whose Time Has Come
Nutrition Science News (Jul 2000)
So-called "super foods" offer the promise of preventing cancer, decreasing heart attacks and improving brain function. Some of the more notable products with health claims now on store shelves include potato chips that enhance memory, new-age drinks that improve your love life, a candy bar that reduces hot flashes, a cookie that helps you bulk up and lean out, and margarine that cuts cholesterol. All of the above claims are due to plant-derived "super nutrients," called phytochemicals, that are helping to blur the line between food and medicine. They appeal to a better-educated public--one growing older, wealthier and more willing to self-medicate with foods and supplements. The question is whether these claims are valid. Do potato chips enhanced with unknown quantities of Ginkgo biloba really improve memory?
All About Phytoalexins
A Chiro.Org article collection
Many of the Polyphenols are also a “phytoalexin”, which are also referred to as secondary metabolites, because they are “organic compounds that are not directly involved in the normal growth, development, or reproduction of the plant”. This is because plants only produce these powerful phytochemicals as a defensive “immune response” to an assault by bugs, bacteria, viruses, molds, or mildews.) Without some external threat stimulus, the plant has no need to produce them. Most of these powerful compounds are polyphenols, and provide a wide-spectrum of health benefits.
Early Intervention with a Multi-Ingredient Dietary Supplement Improves Mood
and Spatial Memory in a Triple Transgenic
Mouse Model of Alzheimer's Disease
Journal of Alzheimer's Disease 2018; 64 (3): 835–857~ FULL TEXT
The increasing global burden of Alzheimer's disease (AD) and failure of conventional treatments to stop neurodegeneration necessitates an alternative approach. Evidence of inflammation, mitochondrial dysfunction, and oxidative stress prior to the accumulation of amyloid-? in the prodromal stage of AD (mild cognitive impairment; MCI) suggests that early interventions which counteract these features, such as dietary supplements, may ameliorate the onset of MCI-like behavioral symptoms. We administered a polyphenol-containing multiple ingredient dietary supplement (MDS), or vehicle, to both sexes of triple transgenic (3xTg-AD) mice and wildtype mice for 2 months from 2–4 months of age. We hypothesized that the MDS would preserve spatial learning, which is known to be impaired in untreated 3xTg-AD mice by 4 months of age.
An Overview of Plant Phenolic Compounds and Their Importance
in Human Nutrition and Management of Type 2 Diabetes
Molecules. 2016 (Oct 15); 21 (10). pii: E1374 ~ FULL TEXT
phenylpropanoid pathways. Plant phenolic compounds can act as antioxidants, structural polymers (lignin), attractants (flavonoids and carotenoids), UV screens (flavonoids), signal compounds (salicylic acid, flavonoids) and defense response chemicals (tannins, phytoalexins). From a human physiological standpoint, phenolic compounds are vital in defense responses, such as anti-aging, anti-inflammatory, antioxidant and anti-proliferative activities. Therefore, it is beneficial to eat such plant foods that have a high antioxidant compound content, which will cut down the incidence of certain chronic diseases, for instance diabetes, cancers and cardiovascular diseases, through the management of oxidative stress. Furthermore, berries and other fruits with low-amylase and high-glucosidase inhibitory activities could be thought of as candidate food items in the control of the early stages of hyperglycemia associated with type 2 diabetes.
Resveratrol Requires Red Wine Polyphenols for Optimum Antioxidant Activity
Journal of Nutrition, Health & Aging 2016; 20 (5): 540–545 ~ FULL TEXT
Overall, our results demonstrate that resveratrol and red wine polyphenols together can protect mammalian cells from oxidative stress, whereas resveratrol alone may have pro-oxidant or anti-oxidant effects depending on concentration. This conclusion is in line with the hypothesis that the benefits of diets rich in fruits and vegetables are attributable to the uptake of phytocomplexes rather than to individual micro-compounds. Several authors have hypothesized that some health effects of plant polyphenols may not require their efficient absorption through the gut and may be due to the direct, protective effects on the intestinal mucosa against oxidative stress or the action of carcinogens.  Studies on human cells show that polyphenols can protect skin fibroblasts and keratinocytes from photo-radiation damage ; that resveratrol protects cells from an oxidative stress by tert-butylhydroperoxide only at high concentrations (in the micromolar range ); and that the protection is enhanced if resveratrol is used in combination with polyphenols such as quercetina and pterostilbene. 
Polyphenols as Therapeutic Molecules in Alzheimer's Disease
Through Modulating Amyloid Pathways
Molecular Neurobiology 2015 (Apr); 51 (2): 466–479 ~ FULL TEXT
Alzheimer's disease (AD) is a complex and multifactorial neurodegenerative condition. The complex pathology of this disease includes oxidative stress, metal deposition, formation of aggregates of amyloid and tau, enhanced immune responses, and disturbances in cholinesterase. Drugs targeted toward reduction of amyloidal load have been discovered, but there is no effective pharmacological treatment for combating the disease so far. Natural products have become an important avenue for drug discovery research. Polyphenols are natural products that have been shown to be effective in the modulation of the type of neurodegenerative changes seen in AD, suggesting a possible therapeutic role. The present review focuses on the chemistry of polyphenols and their role in modulating amyloid precursor protein (APP) processing. We also provide new hypotheses on how these therapeutic molecules may modulate APP processing, prevent Aβ aggregation, and favor disruption of preformed fibrils. Finally, the role of polyphenols in modulating Alzheimer's pathology is discussed.
Nutraceuticals and Their Preventive or Potential Therapeutic Value in Parkinson's Disease
Nutrition Reviews 2012 (Jul); 70 (7): 373–386 ~ FULL TEXT
Parkinson's disease (PD) is the second most common aging-related disorder in the world, after Alzheimer's disease. It is characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta and other parts of the brain, leading to motor impairment, cognitive impairment, and dementia. Current treatment methods, such as L-dopa therapy, are focused only on relieving symptoms and delaying progression of the disease. To date, there is no known cure for PD, making prevention of PD as important as ever. More than a decade of research has revealed a number of major risk factors, including oxidative stress and mitochondrial dysfunction. Moreover, numerous nutraceuticals have been found to target and attenuate these risk factors, thereby preventing or delaying the progression of PD. These nutraceuticals include vitamins C, D, E, coenzyme Q10, creatine, unsaturated fatty acids, sulfur-containing compounds, polyphenols, stilbenes, and phytoestrogens.
Natural Anti-inflammatory Agents For Pain Relief
Surg Neurol Int. 2010 (Dec 13); 1: 80 ~ FULL TEXT
The use of both over-the-counter and prescription nonsteroidal medications is frequently recommended in a typical neurosurgical practice. But persistent long-term use safety concerns must be considered when prescribing these medications for chronic and degenerative pain conditions. This article is a literature review of the biochemical pathways of inflammatory pain, the potentially serious side effects of nonsteroidal drugs and commonly used and clinically studied natural alternative anti-inflammatory supplements. Although nonsteroidal medications can be effective, herbs and dietary supplements may offer a safer, and often an effective, alternative treatment for pain relief, especially for long-term use.
Plant Polyphenols as Dietary Antioxidants in Human Health and Disease
Oxidative Medicine and Cellular Longevity 2009 (Nov); 2 (5): 270–278 ~ FULL TEXT
Polyphenols are secondary metabolites of plants and are generally involved in defense against ultraviolet radiation or aggression by pathogens. In the last decade, there has been much interest in the potential health benefits of dietary plant polyphenols as antioxidant. Epidemiological studies and associated meta-analyses strongly suggest that long term consumption of diets rich in plant polyphenols offer protection against development of cancers, cardiovascular diseases, diabetes, osteoporosis and neurodegenerative diseases. Here we present knowledge about the biological effects of plant polyphenols in the context of relevance to human health.
Phytoalexin-enriched Functional Foods
J Agric Food Chem. 2009 (Apr 8); 57 (7): 2614–2622 ~ FULL TEXT
Functional foods have been a developing area of food science research for the past decade. Many foods are derived from plants that naturally contain compounds beneficial to human health and can often prevent certain diseases. Plants containing phytochemicals with potent anticancer and antioxidant activities have spurred development of many new functional foods. This has led to the creation of functional foods to target health problems such as obesity and inflammation. More recent research into the use of plant phytoalexins as nutritional components has opened up a new area of food science.
Green Tea (Camellia sinensis) Monograph
Alternative Medicine Review 2000 (Aug); 5 (4): 372–375 ~ FULL TEXT
Green tea is produced from steaming fresh leaves at high temperatures, thereby inactivating the oxidizing enzymes and leaving the polyphenol content intact. The polyphenols found in tea are more commonly known as flavanols or catechins. Green tea polyphenols have demonstrated significant antioxidant, anticarcinogenic, anti-inflammatory, thermogenic, probiotic, and antimicrobial properties in numerous human, animal, and in vitro studies.
A Review of Plants Used in the Treatment of Liver Disease: Part 2
Alternative Medicine Review 2000 (Aug); 5 (4): 372–375 ~ FULL TEXT
Botanical medicines have been used traditionally by herbalists and indigenous healers worldwide for the prevention and treatment of liver disease. Clinical research in this century has confirmed the efficacy of several plants in the treatment of liver disease, while basic scientific research has uncovered the mechanisms by which some plants provide their therapeutic effects. This article is Part Two in a review of botanicals used in the treatment of liver disease. Curcuma longa (turmeric), Camellia sinensis (green tea), and Glycyrrhiza glabra (licorice) are reviewed in this installment. Silybum marianum (milk thistle) and Picrorhiza kurroa (kutkin) were reviewed in Part One.
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