Regulation of vitamin C homeostasis during deficiency.

Large cross-sectional population studies confirm that vitamin C deficiency is common in humans, affecting 5%-10% of adults in the industrialized world. Moreover, significant associations between poor vitamin C status and increased morbidity and mortality have consistently been observed. However, the absorption, distribution and elimination kinetics of vitamin C in vivo are highly complex, due to dose-dependent non-linearity, and the specific regulatory mechanisms are not fully understood. Particularly, little is known about how adaptive mechanisms during states of deficiency affect the overall regulation of vitamin C transport in the body. This review discusses mechanisms of vitamin C transport and potential means of regulation with special emphasis on capacity and functional properties, such as differences in the K(m) of vitamin C transporters in different target tissues, in some instances demonstrating a tissue-specific distribution.