Abstract
A randomized and placebo-controlled study was carried out to investigate the changes in the plasma concentrations and urinary excretion of vitamin C during the long-term ingestion of a commercial multivitamin tablet containing vitamin C. Twenty-one healthy males aged 21-24 years were randomly divided into 3 groups. The three groups took either placebo or vitamin C (250 mg or 500 mg) daily for 44 weeks, and measurements were made at 0, 4, 12, 22, 28 and 44 wks. The mean vitamin C plasma concentrations and urinary excretion in the subjects before ingestion were 0.70 ± 0.09 mg/100 ml (mean ± SD) and 12.4 ± 2.8 mg/day, respectively. There were marked increases in the plasma concentrations and urinary excretion at 4 wks, followed by further gradual increases during the experimental period. The mean plasma concentrations were 1.26 ± 0.14 mg/100 ml in the 250 mg group and 1.40 ± 0.19 mg/100 ml in the 500 mg group at 44 wks, and these levels were significantly higher than in the placebo group (0.83 ± 0.10 mg/100 ml). Dose-dependence of the plasma concentrations in the three groups during the experimental period was significant by linear regression analysis. Urinary excretion increased to 134 ± 48 mg/day in the 250 mg group and to 240 ± 71 mg/day in the 500 mg group at 44 wks, which was significantly higher than in the placebo group (13.4 ± 1.9 mg/day) in both cases. Dose-dependent differences among the three groups in the urinary excretion during experimental period were also significant by linear regression analysis. Changes in the plasma concentrations and urinary excretion of vitamin C after the discontinuation of ingestion were also investigated, indicating that there was no withdrawal effect. No side effects were observed in both the placebo and vitamin C groups.
