Effects of vitamin C long-term loading on the serum gamma-glutamyltranspeptidase activity in human subjects

In an attempt to assess dietary effects on the serum enzyme activity of long-term vitamin C supplementation, the serum gamma-GTP(1) fraction was studied in five healthy men. In this study, they were maintained on ordinary meals for the initial one year and the last 7 months of the 43 month experimental period, and on ordinary meals with 1 g/day of vitamin C powder for the intermediate 2 years. The serum gamma-GTP(1) fraction during the first year (ordinary meals alone) was higher than that for the second or third year (ordinary meals with addition of vitamin C). The decrease after vitamin C supplementation was statistically significant. The serum vitamin C concentration tended to rise in winter. Vitamin C supplementation at 1 g/day raised the concentrations up to 1.6 mg/dl on average, where the serum was practically saturated with vitamin C.