Separated this question into its own topic because I know this observation is a favorite for our member RalphDMan . It is relevant to the new product, name escapes me, whose makers believe can stimulate the production of ascorbate from glucose, either by reactivating GULO or other means.
One thing I note is that in humans, the ideal blood glucose is regulated to 90 mg/dl, while the highest vitamin C level is 1.5 mg/dl. So optimal ascorbate is roughly 1 to 2 percent of the glucose in the blood. Even if our livers made more ascorbate (from our now very high sugar intakes) the kidneys would regulate it to no more than 1.5 mg/dl over a short time (30 minute half life).
Owen R. Fonorow, Orthomolecular Naturopath