Ascorbic acid (AA) is an essential micronutrient for man, with many biological roles. It is a powerful antioxidant both directly via scavenging of reactive oxygen species and indirectly through regeneration of other antioxidant systems. Paradoxically, under certain conditions (low concentration in vitro, presence of metal ions) it can exert a pro-oxidant effect, increasing oxidative damage to lipids, DNA and protein. Herein, the effects of vitamin C both in vitro and in vivo are addressed in terms of modulation of oxidative DNA damage, gene expression and protein oxidation. The view of AA as a simple scavenger is outdated, where the arrival of new bioinformatic techniques, heralds a new dawning in our understanding of ascorbate as a potential direct or indirect modulator of gene expression.