Frontiers in polyphenols and cancer prevention.

The health benefits of polyphenols are of much interest currently. To illustrate this point, a search using the term ‘‘polyphenols’’ identified no fewer than 3014 separate hits in PubMed, with 429 reviews, 88 of which appeared since 2005. Among the most highly cited class of polyphenols are the flavonoids, which comprise a large and diverse family of compounds synthesized by plants. Flavonoid subclasses include anthocyanidins in berries and grapes, flavanols in tea, flavanones in citrus fruits, flavonols in onions, flavones in herbs and peppers, and isoflavones in soy (Table 1). High intake of flavonoid-rich foods is associated with reductions in cardiovascular disease risk, but whether polyphenols themselves are cardioprotective is not known (1). Interest is also growing in the potential of polyphenols to protect the aging brain and to lower neurodegenerative disease risk in humans (1). However, the extent to which polyphenols protect against these and other chronic conditions, including cancer, remains open to debate, and clinical data rarely if ever match the promising findings obtained from numerous animal studies. This begs the question as to what causes such a discrepancy.