Handbook of Vitamin C Research

Vitamin C: Dietary Requirements, Dietary Sources, and Adverse Effects 139Alzheimer’s DiseaseThere is evidence in patients with Alzheimer‘s disease (AD) that there is increasedsensitivity of the cerebral cortex to free radicals, perhaps related to lower activity ofantioxidant enzymes such as superoxide dismutase [78, 169]. The major targets for oxidationin the brain are lipids and lipoproteins. Supplementation with vitamin E and C significantlyincreases the concentrations of both vitamins in plasma and CSF and significantly decreasesthe in vitro oxidation of plasma lipoproteins [170]. In contrast, supplementation with vitaminE alone did not decrease lipoprotein oxidation. Two recent studies found patients with ADhave low plasma vitamin C concentrations despite an adequate diet and that supplementationwith vitamin C appears to lower the risk of AD [41, 42].OthersIn critically ill patients and after severe burns, the rapid restoration of depleted ascorbatelevels with high-dose parenteral vitamin C may reduce circulatory shock, fluid requirementsand edema. Oxidative stress is associated with reduced ascorbate levels. Ascorbate isparticularly effective in protecting the vascular endothelium, which is especially vulnerableto oxidative stress. The restoration of ascorbate levels may have therapeutic effects indiseases involving oxidative stress. The rapid replenishment of ascorbate is of special clinicalsignificance in critically ill patients who experience drastic reductions in ascorbate levels,which may be a causal factor in the development of circulatory shock. Supraphysiologicallevels of ascorbate, which can only be achieved by the parenteral and not by the oraladministration of vitamin C, may facilitate the restoration of vascular function in critically illpatients [171].The factors that influence vitamin C levels in a general population of 5527 subjectsvisiting the Changhua Christian Hospital during recent 10 years are listed in Table 1.Correlation analysis of the factors related to elevated vitamin C levels revealed a reciprocaltrend between age and vitamin C level. The analysis also revealed a significant negativeassociation between glucose, insulin, BUN, and urate concentrations, and serum vitamin Clevels. Our results also demonstrated that serological vitamin C content is a predictablebiomarker for hyperlipidemia, hypertension, CVD, Parkinson‘s disease, and familialdementia regardless of genetic predisposition. In addition, there was a negative correlationbetween serum ascorbate level and factors related to lipid metabolism such as oxidized LDL,adiponectin, IMT, and plaque index, a finding supported by previously reported studies [172-175]. It has been reported that serum levels of hsCRP, a marker of inflammation, and VCAM,an adhesion marker, increase when vitamin C concentrations decrease [176]. Based on thedata in our survey, we conclude that vitamin C is an important biomarker for several vasculardiseases and that it dominates the redox states of human physiological conditions.Supplementations from vegetables, fruits and medications are strongly suggested for ahealthy diet