Vitamin C (Ascorbic Acid)

Vitamin C requirement in surgical patients.
Fukushima R, Yamazaki E.
Curr Opin Clin Nutr Metab Care. 2010 Nov;13(6):669-76.

 To summarize recent findings on vitamin C status and assess the requirement and optimal dose of supplementation in surgical patients. Blood vitamin C concentration falls after uncomplicated surgery and further decreases in surgical intensive care unit patients. The decline may be owing to increased demand caused by increased oxidative stress. To normalize plasma vitamin C concentration, much higher doses than the recommended daily allowance or doses recommended in parenteral nutrition guidelines are needed in these patients. In uncomplicated surgical patients, more than 500 mg/day of vitamin C may be required, with much higher doses in surgical intensive care unit patients. In uncomplicated gastrointestinal surgery, continuous parenteral administration of 500 mg/day of vitamin C reduced postoperative oxidative stress as manifested by reduced urinary excretion of isoprostane. In some studies, postoperative atrial fibrillation was prevented after cardiac surgery by perioperative vitamin C supplementation. In critically ill patients, some prospective randomized controlled trials support parenteral supplementation of high doses of vitamin C, E and trace elements. Vitamin C requirement is increased in surgical patients, and the potential advantage of supplementation is to increase the plasma and tissue levels of vitamin C and thereby reduce oxidative stress. Although some clinical benefits of high-dose vitamin C supplementation have been shown in the critically ill, the optimal dose for supplementation and the clinical benefits remain to be investigated in surgical patients. PMID: 20689415

  Antioxidant vitamins and their use in preventing cardiovascular disease.
Farbstein D, Kozak-Blickstein A, Levy AP.
Molecules. 2010 Nov 9;15(11):8098-110.

 Atherosclerosis remains one of the leading causes of death in Western populations. Subsequent to the discovery that oxidative stress plays a pivotal role in the development and progression of atherosclerosis, vitamins C and E, along with other antioxidants, were studied as potential therapies for the disease. However, while in vitro and in vivo studies showed promising antiatherogenic effects for vitamins C and E, clinical trials in which patients were given high doses of vitamin E or C showed no benefit and even possible harm. This review will attempt to summarize the known mechanistic data regarding the biochemical effects of vitamins C and E and their relevance to atherosclerosis, and offer an explanation for the failure of clinical trials to show that supplementation with these vitamins provides any benefit when given indiscriminately. We provide one example of how pharmacogenomics may be used to identify a sub-population which may indeed benefit from antioxidant supplementation. PMID: 21063272

  Ascorbic acid prevents oxidant-induced increases in endothelial permeability.
May JM, Qu ZC.
Biofactors. 2011 Jan;37(1):46-50

 Oxidative stress acutely increases the permeability of the vascular endothelium to large molecules that would not otherwise cross the barrier. Ascorbic acid is an antioxidant that tightens the endothelial permeability barrier, so we tested whether it might also prevent the increase in endothelial permeability due to cellular oxidative stress. Treatment of EA.hy926 endothelial cells cultured on filter inserts with H(2) O(2) , menadione, and buthionine sulfoximine increased endothelial permeability to radiolabeled inulin. Short-term ascorbate loading of the cells to what are likely physiologic concentrations of the vitamin by treating them with dehydroascorbate prevented the increase in endothelial permeability due to these agents. The nonphysiologic antioxidants dithiothreitol and tempol also prevented increases in endothelial barrier permeability induced by the agents. These results suggest that oxidative stress induced directly by oxidants or indirectly by glutathione depletion impairs endothelial barrier function and that intracellular ascorbate may serve to prevent this effect. PMID: 21328627
Copyright © 2010 International Union of Biochemistry and Molecular Biology, Inc.

  New insight on vitamin C in patients with chronic kidney disease.
Handelman GJ.
J Ren Nutr. 2011 Jan;21(1):110-2.

 Patients on dialysis often develop anemia, which is accompanied by the development of substantial iron stores after administration of intravenous iron. This can be remedied in some instances with administration of supplemental vitamin C, either intravenously or orally. This is because of the mobilization of stored iron, which results in correction of anemia and in improvement of iron-indices of red cells and reticulocytes. The short red cell survival often seen in patients on dialysis creates a situation in which very large amounts of iron are needed to be supplied for new erythropoiesis, and vitamin C therefore contributes to necessary iron delivery. The safety of this therapy needs careful study so as to determine vitamin C dosage that is effective and also avoids complications of oxalosis. PMID: 21195931 Copyright © 2011 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.

  Vitamin C consumption does not impair training-induced improvements in exercise performance.
Roberts LA, Beattie K, Close GL, Morton JP.
Int J Sports Physiol Perform. 2011 Mar;6(1):58-69.

 To test the hypothesis that antioxidants can attenuate high-intensity interval training-induced improvements in exercise performance. Two groups of recreationally active males performed a high-intensity interval running protocol, four times per week for 4 wk. Group 1 (n = consumed 1 g of vitamin C daily throughout the training period, whereas Group 2 (n = 7) consumed a visually identical placebo. Pre- and posttraining, subjects were assessed for VO2max, 10 km time trial, running economy at 12 km/h and distance run on the YoYo intermittent recovery tests level 1 and 2 (YoYoIRT1/2). Subjects also performed a 60 min run before and after training at a running velocity of 65% of pretraining VO2max so as to assess training-induced changes in substrate oxidation rates. Training improved (P < .0005) VO2max, 10 km time trial, running economy, YoYoIRT1 and YoYoIRT2 in both groups, although there was no difference (P = .31, 0.29, 0.24, 0.76 and 0.59) between groups in the magnitude of training-induced improvements in any of the aforementioned parameters. Similarly, training also decreased (P < .0005) mean carbohydrate and increased mean fat oxidation rates during submaximal exercise in both groups, although no differences (P = .98 and 0.94) existed between training conditions. Daily oral consumption of 1 g of vitamin C during a 4 wk high-intensity interval training period does not impair training-induced improvements in the exercise performance of recreationally active males. PMID: 21487150