Plant polyphenols in cancer and heart disease: implications as nutritionalantioxidants

Certain dietary antioxidants such as vitamin E and vitamin C are important for maintaining optimum health. There is now much interest in polyphenolic products of the plant phenylpropanoid pathway as they have considerable ant ioxidant activity in vitro and are ubiquitous in our diet. Rich sources inc lude tea, wine, fruits and vegetables although levels are affected by speci es, light, degree of ripeness, processing and storage. This confounds the f ormulation of databases for the estimation of dietary intakes. Most attenti on to date has focused on the flavonoids, a generic term which includes cha lcones, flavones, flavanones, flavanols and anthocyanins. There is little c onvincing epidemiological evidence that intakes of polyphenols are inversel y related to the incidence of cancer whereas a number of studies suggest th at high intakes of flavonoids may be protective against CHD. In contrast, n umerous cell culture and animal models indicate potent anticarcinogenic act ivity by certain polyphenols mediated through a range of mechanisms includi ng antioxidant activity, enzyme modulation, gene expression, apoptosis, upr egulation of gap junction communication and P-glycoprotein activation. Poss ible protective effects against heart disease may be due to the ability of some polyphenols to prevent the oxidation of LDL to an atherogenic form alt hough anti-platelet aggregation activity and vasodilatory properties are al so reported. However, some polyphenols are toxic in mammalian cells. Thus, until more is known about their bioavailability, metabolism and intracellul ar location, increasing intakes of polyphenols by supplements or food forti fication may be unwise.