Flavonoids are widely distributed plant pigments and tannins occurring in barks, roots, leaves, flowers, and fruits. Their roles in plants include photoprotection and contributing to the plant color. Consequently, our diet contains flavonoids which can be found in a variety of foods from green vegetables to red wine [49].

Despite the fact that flavonoids have been used in traditional medicine for several centuries, it was not until 1936 that their first biological activity, the vitamin C-sparing action, was described by Rusznyak and Szent-Gyorgyi [50]. As a result, they received the name of ''vitamin P.'' Flavonoids, also referred to as plant polyphenols, have been recognized as potent antioxidants. Their free radical-scavenging and metal-chelating activities have been extensively studied. Nonetheless, given their polyphenolic structure (Fig. 4), the electron- and hydrogen-donating abilities constitute the major feature of their antioxidant properties [51]. By opposition to the antioxidants previously described, flavonoids

Figure 4 Chemical structure of catechin, a flavane, as an example of a flavonoid. Flavanes share a common base structure (rings A, B, C) that is hydroxylated in different patterns.

are not part of the endogenous antioxidant system but still interact with it through the antioxidant network (see the following paragraph).

Among the applications found in traditional medicine, flavonoids account for antiinflammatory, antiphlogistic, and wound-healing functions [52]. Their effect on skin inflammation has been thought, for a long time, to be limited to the inhibition of the activity of 5-lipoxygenase and cyclo-oxygenase [49]. However, recent studies suggest a more subtle mode of regulation of the inflammatory reaction by flavonoids. In fact, flavonoids such as silymarin, quercetin, genistein, and apigenin are effective inhibitors of NF-kB, a proinflammatory transcription factor, thereby reducing the transcription of proinflamma-tory genes and preventing inflammation [53-55].

Oral supplementation and topical application of green and black tea polyphenols show beneficial effects against UVR-induced skin carcinogenesis in mice [56-58]. In addition, these flavonoids and silymarin were found to prevent UVR-induced inflammation as well as ornithine decarboxylase expression and activity [59], all of these events being potential contributors to carcinogenesis [60].

Procyanidins, also named condensed tannins, are flavonoids found in, e.g., pine bark (Pycnogenol), grape seeds, and fruits. By direct protein interaction, they were shown to protect collagen and elastin, two dermal matrix proteins, against their degradation [61]. Furthermore, some of these procyanidins exhibit a remarkable effect on follicle hair proliferation [62] thus extending the therapeutic applications of flavonoids to alopecia. Although the flavonoids are not part of our endogenous antioxidant defenses, they display a broad spectrum of properties particularly helpful in preventing UVR-caused deleterious effects in human skin.

Hair Loss Prevention

Hair Loss Prevention

The best start to preventing hair loss is understanding the basics of hair what it is, how it grows, what system malfunctions can cause it to stop growing. And this ebook will cover the bases for you. Note that the contents here are not presented from a medical practitioner, and that any and all dietary and medical planning should be made under the guidance of your own medical and health practitioners. This content only presents overviews of hair loss prevention research for educational purposes and does not replace medical advice from a professional physician.

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