There are no data to quantify directly the dose-response relation between vitamin C intake and in vivo antioxidant protection. Therefore, the criterion chosen for the EAR is the vitamin C intake that maintains near-maximal neutrophil vitamin C concentrations with minimal urinary loss. Since leukocyte ascorbate, which includes neutrophil ascorbate, correlates well with liver and body pool ascorbate (Omaye et al., 1987), this criterion should provide for adequate in vivo antioxidant protection to body tissues while minimizing excess urinary vitamin excretion. Vitamin C intakes greater than the urinary excretion threshold provide little or no increase in the ascorbate body pool (Baker et al., 1969; Kallner et al., 1979). A vitamin C intake that meets the above criteria is estimated from a controlled vitamin C dose-response study described below.
The requirement for vitamin C based on the above criteria can be estimated from the data reported by Levine et al. (1996a) in which