Effect of large doses of ascorbic acid in man on some nitrogenous components of urine

Base-line values for the excretion of urea N, amine N, creatinine, uric acid and cysteine were measured in three consecutive 24-h urine collections from 16 healthy volunteers. The subjects then took 1 g ascorbic acid three times a day after meals for 7 days. Twenty-four hour urine samples were collected on the 1st, 3rd, 5th and 7th days of the study. Where possible, a further 24-h sample was collected a minimum of 10 d after the end of the study. Administration of 3 g/d of ascorbic acid had no effect on urine volume, pH or the excretion of urea, amino N or creatinine. It caused a transient increase in uric acid excretion but an immediate and sustained increase in the excretion of cysteine. This study provides no evidence for an effect of high doses of ascorbic acid on urinary stone formation but does suggest competition for important co-factors in the metabolism of drugs.