Blood levels and bioavailability of ascorbic acid after administration of a sustained-release formulation to humans.

Plasma and whole blood concentrations of ascorbate have been measured after administration of 1000 mg of the vitamin as standard or sustained-release capsule formulations to human subjects. A peak of mean whole blood and plasma concentrations of 8.5 mug/ml and 5.7 mug/ml respectively (corrected for predose concentrations of "endogenous" ascorbate) occurred at 12 h and 6 h respectively after administration of a sustained-release formulation. After administration of a standard formulation, the peak of mean whole blood and plasma concentrations of 9.4 mug/ml and 8.6 mug/ml respectively occurred at 4 h. In whole blood, mean concentrations of ascorbate declined with a half-life of about 34 h. The bioavailability of ascorbate from the sustained-release formulation was 149% and 180% of that from the standard formulation by calculation from whole blood and plasma concentration data respectively.