Vitamin C: poison, prophylactic or panacea?

Ascorbate is an essential enzyme cofactor but is often also regarded as an important antioxidant in vivo, protecting against cancer by scavenging DNA-damaging reactive oxygen species. Recent studies suggest that ascorbate sometimes increases DNA damage in humans. Although there is no evidence that any of these effects are deleterious to humans, we might need to change our thinking about the mechanisms of the antioxidant action of ascorbate in vivo.