Antioxidant Actions of Polyphenols in Humans

Many polyphenols are potent antioxidants in foods and model systems and they have therefore very naturally been linked with the hypothesis that their redox activities may confer them with specific health benefits. Their prevalence in plant derived foods, which are generally accepted as healthy has supported this view and inspired researchers to conduct human intervention trails with polyphenol rich food items in order to investigate their ability to counteract oxidative stress. Several biomarkers have gained widespread use to assess oxidative damage and antioxidative defence capabilities in humans. These markers pioneer our knowledge about factors related to oxidative stress in proteins, lipids and DNA and present results indicate that oxidative damage may be very localised and that refined markers may be necessary in order to disentangle the complex local factors which determine the extent of oxidative damage in different molecular structures. The present text reviews the human short-term intervention studies with polyphenol-rich foods, which address their impact on biomarkers of oxidative damage and antioxidative defence. None of the oxidative damage markers seem to be consistently affected by polyphenol-rich foods or to be consistently related to one another. The most consistent finding regarding antioxidative defence markers is a postprandial effect on plasma antioxidative capacity after ingestion of foods rich in catechins and complex procyanidins.