Ascorbic acid status: biochemical and clinical considerations.

Abstract

Ascorbic acid (AA) plus dehydroascorbic acid (DHAA) was stable in whole blood in unopened vacutainer tubes. Oxidation of DHAA in plasma was irreversible and rapid at 25 degrees C but not at 4 degrees C. The half-life of AA + DHAA in total parenteral nutrition solutions was greater than 24 h. Conditions are described for dithiothreitol reduction of DHAA followed by assay of total AA, with DHAA being determined by difference. DHAA accounted for less than 5% of the total plasma AA + DHAA in both healthy and diabetic subjects. Infection and postpartum-induced stresses resulted in no significant change in the AA content of polymorphonuclear leukocytes (PMN) per unit of blood but AA content per cell was decreased. When glucose concentration was increased, the Km for AA uptake by PMNs doubled. These chemical and physiological factors combined with the rapid movement of the vitamin between plasma and cells suggest that a reliable indicator of AA status remains to be identified.