To simplify a very complex system, there are four main uptake paths for VC (passive diffusion, facilitated diffusion, active transport and recycling through the kidneys). Difference subsystems (brain, lungs, heart, muscles etc.) can each tolerate different levels of vitamin C and regulate levels through the use of different uptake paths. These levels are lower than the levels discussed in the paper obtained through intravenous means. If the body were exposed to long term high levels as discussed in the paper, there would be concerns of damage to many of the systems that need to regulate much lower levels. If one where to ingest large doses it would mostly go through the recycle system and be removed by the kidneys before it would get to the sub-systems.