Metabolism and requirements of ascorbic acid in man.

The metabolism and absorption of ascorbic acid in man are reviewed. The daily requirement of ascorbic acid in male non-smoking volunteers was studied by following the kinetics of a single dose of (1-14C) ascorbic acid under steady-state conditions. A diet low in vitamin C and daily supplements of ascorbic acid (30-180 mg) were given. The time course of elimination of radioactivity from plasma and urinary excretion data were used to calculate kinetic parameters. The overall half-life was calculated as 10 - 20 days and is dependent of plasma ascorbate levels. The body pool approached 20 mg/kg body weight at a plasma ascorbate concentration of 0.9 mg/dl and was maintained by a total turnover of 60 mg/d. The necessary daily intake of ascorbic acid to match this turnover is 70-80 mg, since absorption is incomplete (80-90%). Therefore, to cover at least 95% of the non-smoking male population a daily intake of 100 mg ascorbic acid is required. Similar studies have been carried out in smokers known to have lowered plasma ascorbate levels. Results suggest that the requirement of ascorbic acid is increased in smokers--a daily intake of 140 mg ascorbic acid is thought to be adequate non-smoking male population a daily intake of 100 mg ascorbic acid is required. Similar studies have been carried out in smokers known to have lowered plasma ascorbate levels. Results suggest that the requirement of ascorbic acid is increased in smokers-a daily intake of 140 mg ascorbic acid is thought to be adequate.