Identification of the factors responsible for the in vitro pro-oxidant and cytotoxic activities of the olive polyphenols oleuropein and hydroxytyrosol

► The in vitro effects of olive polyphenols oleuropein and hydroxytyrosol are due to H2O2 production. ► H2O2 causes oxidative DNA damage and a decrease in cell viability of cancer and normal cells alike. ► Sodium bicarbonate is essential for the production of H2O2 by olive polyphenols. ► Our results challenge previous data interpretations of in vitro studies with olive polyphenols.