Phenolics: prooxidants or antioxidants?

Both essential and nonessential dietary antioxidants have been suggested to be beneficial for health. However, studies show that many antioxidants can also exhibit prooxidant behavior under certain conditions. The antioxidant/prooxidant activity of phenolics is dependent on such factors as metal-reducing potential, chelating behavior, pH, and solubility characteristics. These factors, in addition to bioavailability and stability in tissues, should be considered when evaluating the potential bioactivity of dietary phenolics.