THE VITAMIN C REQUIREMENT OF MAN. ESTIMATED AFTER PROLONGED STUDIES OF THE PLASMA CONCENTRATION AND DAILY EXCRETION OF VITAMIN C IN 3 ADULTS ON CONTROLLED DIETS1

Abstract

The daily excretion and plasma conc. of vit. C were detd. on 3 [male] adults on control diets and daily fed varying amts. of vit. C as ascorbic acid. With amts. of vit. C below 100 mg. the 24-hr. excretion did not exceed an aver. of 13 mg. With more than 100 mg. there was a sharp rise in the excretion which continued to parallel any increase in the amt. ingested. On less than 100 mg. it was impossible to maintain a plasma level of 1.0 mg.%; hence 100 mg. of vit. C is suggested as the optimum daily intake. On 50 mg. of vit. C, the plasma conc. averaged 0.4 mg.%. As the patients were normal and without symptoms of vit. C deficiency, this plasma level may be considered the lower limit of normal. At this level, however, the tissues are not saturated with vit. C and saturation apparently does not occur until the plasma conc. is 1.0 mg.%.