Dietary polyphenols: Antioxidants or not?

Population studies have shown a strong association between dietary intake of polyphenols and reduced risk of cardiovascular disease. These associations have been confirmed to some extent by intervention studies which have shown improvements in vascular function and blood pressure with certain polyphenols or food extracts rich in polyphenols. The mechanisms involved in the bioactivity of dietary polyphenols is still under active investigation. It is unlikely that polyphenols act as antioxidants in vivo. Evidence suggests that dietary polyphenols or their metabolites act as signalling molecules and can increase nitric oxide bioavailability and induce protective enzymes. This review will outline some of the key issues in dietary polyphenol research that suggest mechanistic insights into the action of these bioactive compounds. There are a number of issues that remain to be resolved in bridging the gap between observational studies and intervention trials using food extracts or pure polyphenol compounds.