However, it has been suggested that the consumption of large amounts of a single dietary antioxidant supplement is deleterious to human health. Polyphenols with particular structures exhibit prooxidant activity under certain conditions, which may contribute to their potential toxicity and carcinogenicity [61].
The current consensus from epidemiological and human studies is that a low risk of cancer is more strongly related to a diet rich in multiple antioxidants than to one supplemented with an individual antioxidant [58].
The intervention of multistage carcinogenesis by modulating intracellular signaling pathways may provide a molecular basis for chemoprevention with a wide variety of dietary polyphenols. Such mechanisms must be characterized before the therapeutic use of antioxidative phytochemicals can be implemented. This article reviews the intracellular signaling pathways that respond to oxidative stress and how they are modulated by naturally occurring polyphenols. The possible toxicity and carcinogenicity of polyphenols are also discussed.
https://iubmb.onlinelibrary.wiley.com/doi/pdf/10.1002/biof.5520260202
