Fig. 3.

Comparison of vitamin C and an average low molecular weight drug with regard to tissue concentration. Plots are approximations for illustrative purposes only. A: Following administration, a normal drug will quickly distribute to the tissue by passive diffusion until equilibrium is reached. Subsequently, the drug is cleared from the tissue with a half-life equal to that of plasma elimination [97]. B: The maximal tissue concentration is proportional to the dose. C & D: In a vitamin C sufficient individual, tissue concentration will be at their steady state and not subject to significant fluctuation unless an insufficient dose is provided. The maximal tissue concentration of individual tissues depends on SVCT configuration and expression and display saturation kinetics with increasing doses [7,10,11]. E: In a vitamin C deficient individual, tissue concentrations will quickly increase when vitamin C is provided depending on SVCT2 expression and tissue priority [7]. If vitamin C administration is discontinued, the tissue concentration will gradually decline but much slower than from the plasma compartment. Some tissues such as the brain have a remarkable ability to retain vitamin C against an increasing concentration gradient as a result of emerging deficiency [92,99]. F: In a vitamin C deficient individual, steady state level will be reached when sufficient vitamin C is provided. Steady state concentration of the tissue does not exceed saturation level.