FIGURE 5-2 The effect of varying extracellular ascorbate concentrations on inhibition of superoxide produced by activated neutrophils. The range of normal human plasma ascorbate concentrations is shown within the arrows.

SOURCE: Adapted from Anderson and Lukey (1987).

L (0.5, 1.1, 2.2, and 5.0 mg/dL), respectively, without any effect on intracellular bacterial killing (Anderson and Lukey, 1987). This indicates that antioxidant protection is increasingly provided as ascorbate concentrations increase, with the greatest change in protection seen for ascorbate concentrations between 28 and 57 µmol/L (0.5 and 1.0 mg/dL).

Although similar dose-response data for leukocyte ascorbate levels are not available, the limited data from Levine et al. (1996a), seen in Figure 5-3 and Figure 5-4, show that plasma and neutrophil ascorbate concentrations are both directly related to vitamin intake between about 50 and 90 mg/day. The concentrations were measured by a sensitive high-pressure liquid chromatography assay with electrochemical detection. Therefore, increasing neutrophil ascorbate concentrations within this range should provide for increased protection against phagocyte-derived oxidant damage.