A polyphenol antioxidant is a type of antioxidant containing a polyphenolic substructure. Numbering over 4,000 distinct species, many of these compounds have antioxidant activity in vitro but are unlikely to have antioxidant roles in vivo.[1][2] Rather, they may affect cell-to-cell signaling, receptor sensitivity, inflammatory enzyme activity or gene regulation.[2][3]
From about 500 million years ago, freshwater and terrestrial plants slowly optimized the production of “new” endogenous antioxidants, such as ascorbic acid (vitamin C), polyphenols (including flavonoids), tocopherols, etc. A few of these appeared more recently, in the last 50–200 million years, in fruits and flowers of angiosperm plants. In fact, the angiosperms (the dominant type of plant today) and most of their antioxidant pigments evolved during the late Jurassic period.
The main source of polyphenols is dietary, since they are found in a wide array of phytochemical-bearing foods. For example, honey; most legumes; fruits such as apples, blackberries, blueberries, cantaloupe, pomegranate, cherries, cranberries, grapes, pears, plums, raspberries, and strawberries; and vegetables such as broccoli, cabbage, celery, onion and parsley are rich in polyphenols. Red wine,[4] chocolate, white tea, green tea, olive oil, argan oil, bee pollen and many grains are sources. Ingestion of polyphenols occurs by consuming a wide array of plant foods; correspondingly, the role of dietary supplements as a method of realizing these health benefits is the subject of considerable discussion.
The regulation theory considers a polyphenol antioxidant’s ability to scavenge free radicals and up-regulate certain metal chelation reactions. Various reactive oxygen species, such as singlet oxygen, peroxynitrite and hydrogen peroxide, must be continually removed from cells to maintain healthy metabolic function. Diminishing the concentrations of reactive oxygen species can have several benefits possibly associated with ion transport systems and so may affect redox signaling.
Consuming dietary polyphenols may be associated with beneficial effects in higher animal species:
It is difficult to evaluate the physiological effects of specific polyphenolic antioxidants, since such a large number of individual compounds may occur even in a single food and their fate in vivo cannot be measured. For example, over sixty different chemically distinct flavonoids are known to occur in a given red wine. The polyphenol content of wines is usually evaluated by the Folin-Ciocalteu reagent which correlates well with alternative chemical and biological procedures for determining antioxidant potential.[11]
Other more detailed chemical research has elucidated the difficulty of isolating individual polyphenolic antioxidants. Significant variation in polyphenol content occurs among various brands of tea may underlie[12] inconsistencies of epidemiological studies implying beneficial health effects of polyphenol antioxidants of green tea blends. The Oxygen Radical Absorbance Capacity (ORAC) test is a laboratory indicator of antioxidant potential in foods and dietary supplements. However, ORAC results cannot be confirmed to be physiologically applicable.[2]
There is debate regarding the total body absorption of dietary intake of polyphenolic compounds. While some indicate potential health effects of certain specific polyphenols, most studies demonstrate low bioavailability and rapid excretion of polyphenols, indicating their potential roles only in small concentrations in vivo.[1][2][3] More research is needed to understand the interactions between a variety of these chemicals acting in concert within the human body. In particular there is evidence that some combinations of foods may inhibit efficient intestinal transfer of certain polyphenol antioxidants; refined sugars, for example, have been shown to impede this uptake under certain circumstances.[13] Furthermore caution should be exercised in attempting diets depending largely on dietary supplements as opposed to a broad array of food sources, since the quality and concentrations of beneficial chemicals in some commercial products is subject to question.
There is little evidence that reactive oxygen species play a role in the process of skin aging.[14] The skin is exposed to various exogenous sources of oxidative stress, including ultraviolet radiation whose spectral components may be responsible for the extrinsic type of skin aging, sometimes termed photoaging. It has been shown not only that increased levels of protective low molecular weight antioxidants through a diet rich in phytochemicals, but also by direct topical dermal application of low molecular weight antioxidants, notably vitamins C and E, as well as lipoic acid, may confer protective effects against oxidative stress.[14] However, controlled long-term studies on the efficacy of low molecular weight antioxidants in the prevention or treatment of skin aging in humans are absent.
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