OP033 BIOAVAILABILITY OF ANTIOXIDANTS VARIES WITH NUTRITIONAL STATUS IN ADOLESCENTS?

Abstract

Rationale: The adequate dose and the effectiveness of vitamin C administration in postsurgical patients are not clear. We investigated an adequate vitamin C dose during PPN therapy in patients after gastrointestinal surgery by measuring blood concentrations and urine excretions of vitamin C. We also sought to identify the effects of vitamin C on the oxidative status. Methods: In a randomized trial, 2 days after undergoing gastrointestinal surgery, 16 patients started to receive a 5-day continuous intravenous infusion of vitamin C, either 100 or 500mg/day. Blood concentrations of vitamin C and inflammatory and immunological parameters were measured preoperatively, next day of surgery, and 3 and 5 days after starting administration of vitamin C (Day3 and Day5). Also, excretions of vitamin C and oxidative stress markers in 24-hour, cumulative urine samples, collected and stored under light protection at 0oC were measured on Day3 and Day5. Results: Mean blood vitamin C concentration decreased markedly after surgery. The concentration returned to normal on Day 3 and on Day 5 in the 500-mg group and only on Day 5 in the 100-mg group. Concentrations differed significantly between the groups on Day 3 and on Day 5 (P< 0.001 for both days). Urinary vitamin C excretion was above normal on both days in the 500mg group, but it never reached normal in the 100mg group (P< 0.001 for both days). Urinary excretion of 8-isoprostane, a marker of oxidative stress, was significantly lower in the 500-mg than in the 100-mg group on Day3 (P= 0.002). Conclusion: Vitamin C dose of 500mg/day, not 100mg/ day, is adequate for patients undergoing gastrointestinal surgery and receiving PPN therapy. Vitamin C may decrease postsurgical oxidative stress.