ABSTRACT
Vitamin C (ascorbic acid, ascorbate) is an essential micronutrient and versatile reducing agent found in food and dietary supplements. The current recommended daily allowance of vitamin C in the United States is 90 mg for men and 75 mg for women [1], with no observed clinical benefit to consuming oral doses above the recommended daily allowance for healthy individuals [2]. At physiologic concentrations in well-nourished humans (50–80 μM) [2], vitamin C exists approximately 99% of the time as the ascorbate anion [3]. Enzymatically, vitamin C is a specific electron donor to at least 16 mammalian enzymes and to three additional fungal enzymes. As a chemical electron donor, vitamin C may have both antioxidant and pro-oxidant actions [2,4]. While vitamin C can reduce reactive oxygen species at micromolar concentrations functioning as an antioxidant, it can also act as a pro-oxidant at higher millimolar concentrations, killing cancer cells in vitro and slowing in vivo tumor growth.
