Recommendations for Vitamin C Intake

To the Editor: The comments by Dr Levine and colleagues¹ regarding an appropriate recommended daily allowance for vitamin C are controversial. The data reported in the previous study by Levine et al² support earlier published data,³ and indicate that plasma saturation with vitamin C does not occur until consumption of a dosage of 500 mg twice a day. A critical protective effect of vitamin C is its synergistic role in regenerating vitamin E in plasma low-density lipoprotein. Oxidation of plasma low-density lipoprotein is a key step in deposition of plaque in arteries. Thus, maintaining a maximal level of vitamin C in the plasma significantly reduces free-radical generation leading to low-density lipoprotein oxidation.⁴ There is considerable evidence that taking vitamins C and E in supplement form may reduce the risk of cancer, heart disease, and death.⁵ Dosages of less than 500 mg twice a day do not provide plasma saturation, and do not reduce free-radical formation in plasma as effectively.