There are a network of nutrients – some may not even be essential – that are involved in the proper absorption, distribution (all the way to subcellular distribution), metabolism and excretion of vitamin C.
In turn vitamin C is a member of other nutrients’ ADME networks. The RDA for vitamin C must make an account of both types of ADME networks. For example, the vitamin C requirement may be lower when vitamin C’s ADME network is functioning well, and the requirement for C may be higher when one of the nutrients in whose ADME network C is a participant is unbalanced (low or high).
To study the effect of high dose vitamin C on the body there is a pre-requisite of showing that vitamin C’s ADME network is in place and functioning properly. Indeed, one may need to boost the network nutrients making up vitamin C’s ADME network to accommodate higher vitamin C concentrations.
And to study the effect of high dose C on free radical quenching, for example, the functionality of the entire antioxidant network must be validated first. Adding a vast excess of C to a network deficient in another key component of the antioxidant network is not likely to improve the quenching of harmful free radicals. In addition, it may be necessary to boost the levels of the other free radical quenchers in order to accommodate higher vitamin C levels.