The Multifaceted Biological Roles of Vitamin C

Shiu-Ming Kuo

doi:10.4172/2155-9600.1000231

Abstract

Scurvy due to severe vitamin C (ascorbic acid) deficiency among sailors was one of the earliest documented occupational diseases. This review first discussed some reduction potential-based biochemical activities of vitamin C such as assisting the post-translational collagen modification as well as acting as an antioxidant and pro-oxidant. These known activities of vitamin C were then used to address recent outcomes of vitamin C clinical trials on the prevention and treatment of non-scurvy diseases such as cardiovascular diseases and cancer. The pro-oxidant activity may contribute to the adverse effect of high-level vitamin C supplementation in clinical trials.

Highlights

Vitamin C deficiency is known to cause scurvy in humans [1]
While prolyl hydroxylase has a lower affinity for vitamin C with Km of 100 μM, lysyl hydroxylase has a Km of 5 μM, which is within the physiological range expected for the prevention of scurvy [21]
While some forms of collagens have been linked to the inhibition of tumor growth [63], epidemiological studies examining the range of vitamin C intake that can affect the collagen maturation found either a small reduction or no change in cancer risk at higher dietary vitamin C intake [64,65,66]

Summary

Introduction

Vitamin C (ascorbic acid) deficiency is known to cause scurvy in humans [1]. Guinea pigs need dietary vitamin C as well and historically serve as the only mammalian model for vitamin C studies. When mice face excessive vitamin C loss, a compensatory change in the endogenous synthesis of ascorbic acid has been reported [6]. These fundamental differences between species make the extrapolation of results from vitamin C studies on rats and mice to humans challenging. Natural mutations and genetic engineering have created experimental models that facilitated the understanding of vitamin C Of these ascorbic acid-producing species, a disruption in the endogenous synthesis (Gulo-/-) led to the vitamin C requirement. Many seemingly contradictory findings on vitamin C have been demonstrated in the cell-free or cell culture experiment These reactions may have little biologically relevance partly because of the poor bioavailability of vitamin C at high doses. Even an intravenous injection of 0.5 g vitamin C/kg body weight (i.e., 35 g for a 154 lb individual) only transiently raised the plasma concentration to 8 mM [14]

Biochemical and Chemical Activities of Vitamin C

Vitamin C as an antioxidant

Cardiovascular diseases

Findings

Conclusions