Review: When is an antioxidant not an antioxidant? A review of novel actions and reactions of vitamin C

Free Radic Res. 2005 Jul;39(7):671-86. doi: 10.1080/10715760500104025.


Vitamin C (or ascorbic acid) is regarded as the most important water-soluble antioxidant in human plasma and mammalian cells which have mechanisms to recycle and accumulate it against a concentration gradient, suggesting that the vitamin might also have important intracellular functions. In this review we summarize evidence from human trials that have attempted an association between vitamin C supplementation and an effect on biomarkers of oxidative DNA damage. Most studies reviewed herein showed either a vitamin C-mediated reduction in oxidative DNA damage or a null effect, whereas only a few studies showed an increase in specific base lesions. We also address the possible beneficial effects of vitamin C supplementation for the prevention of cancer and cardiovascular disease. Finally, we discuss the contribution of cell culture studies to our understanding of the mode of action of vitamin C and we review recent evidence that vitamin C is able to modulate gene expression and cellular function, with a particular interest in cell differentiation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Antioxidants / metabolism*
  • Antioxidants / pharmacology*
  • Ascorbic Acid / metabolism*
  • Ascorbic Acid / pharmacology*
  • DNA Damage*
  • Dietary Supplements
  • Gene Expression
  • Humans
  • Oxidants / metabolism
  • Oxidants / pharmacology
  • Oxidative Stress
  • Signal Transduction / physiology


  • Antioxidants
  • Oxidants
  • Ascorbic Acid