Supplementary Facts: Polyphenols' Power Is in Food and Drink, Not in Pill Form

Gayle Nicholas Scott, PharmD


November 21, 2016

A Refresher on Polyphenols

"Phytochemicals" are widely marketed as dietary supplements. Advertisements for these supplements often contain such terms as "polyphenol," "bioflavonoid," and a myriad of others that may read as vague or mysterious to most. But what do these terms really mean?

Phytochemicals are chemicals from plants (phyto being the Greek word for "plant") and comprise a wide variety of biologically active substances. Humans and animals cannot synthesize phytochemicals. Examples of phytochemicals include the phytosterols (eg, sitosterol), which are chemically related to cholesterol; terpenes (eg, eugenol); and the indoles, which may mediate the proposed anticancer effect of cruciferous vegetables, such as broccoli.

The most studied class of phytochemicals is polyphenols. The aim of this brief pharmacognosy review is to describe the various classes of polyphenols and subclasses of flavonoids, as well as provide some examples of foods in which they can be found.

To refresh organic chemistry-challenged minds, polyphenols are characterized by the presence of multiple phenolic rings (ie, benzene rings with hydroxyl groups). They are produced by plants to defend against ultraviolet radiation or pathogens. Polyphenols are responsible for some of the color, flavor, odor, and bitterness of fruits, vegetables, grains, and such beverages as tea and coffee. They function as antioxidants and have been reported to bestow health benefits, including protection from cardiovascular disease, cancer, infections, and a variety of other conditions.

The polyphenol content of food is affected by multiple variables, including degree of ripeness at harvest, rainfall, and sun exposure. Polyphenol concentrations are also affected by factors not inherent to the foods themselves, such as how they are stored or cooked.[1,2]

Several hundred polyphenols have been identified in edible plants. The chemical class can be grouped on the basis of the number of phenol rings and structural features of linkages. Many are in the form of glycosides (phenolic groups linked to a sugar); carbohydrates and organic acids can be bound in different positions on polyphenol skeletons.[1] Polyphenols are classified as phenolic acids, stilbenes, lignans, and flavonoids (Figure). Flavonoids, which can be further grouped into six subclasses, are the best studied.

Figure. Polyphenol classification system.


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