Handbook of Vitamin C Research

In: Handbook of Vitamin C Research: ISBN: 978-1-60741-874-0Editors: Hubert Kucharski and Julek Zajac©2009 Nova Science Publishers, Inc.Chapter VPro-Oxidant vs. Antioxidant Effectsof Vitamin CBorut Poljsak 1 and John G. Ionescu 2, 31 Laboratory for ageing process research, Chair of Environmental Health, Facultyof Health Studies, University of Ljubljana, Slovenia2 Spezialklinik Neukirchen, Neukirchen, Germany3 Dept. of Medical Nutrition, Donau University Krems, AustriaAbstractVitamin C (L-ascorbic acid) protects human health by scavenging toxic free radicalsand other reactive oxygen species (ROS) formed in cell metabolism. On the other side, itis well established by in vitro experiments that vitamin C is reactive with free iron andproduces free radicals, while causing oxidative damage to biomolecules. The interactionof ascorbic acid with transition metal ions could promote their reduction, accompaniedby increased H 2 O 2 production and consequently OH˙‘ formation. The mixture of metalions and ascorbate in some vitamin pills has been claimed to generate OH˙‘ once the pillsdissolve and several reports suggest increases in DNA damage in healthy humanssupplemented with vitamin C and iron salts. In epidemiologic studies it is often assumedthat antioxidant vitamins act by lowering oxidative damage, but evidence in support ofthis contention is not provided or is contradictory. Many studies show an inverserelationship between mortality and vitamin C intake indicating a protective antioxidantactivity. On the other side several reports show no significant relationship aftercontrolling for confounding variables. Therefore there is still debate on whethersupplements of vitamin C could act as antioxidant or pro-oxidant in vivo. Recent researchsuggests that 3 factors are responsible for the pro- or antioxidant behaviour of vitamin Cin biological systems, e.g. cellular environment:1.) the redox potential of the cellularenvironment (oxidosis/redosis), 2.) the presence or absence of transition metals and 3.)the local concentration of ascorbate. This may also explain the observed quite specificpro-oxidant activity of high dose intravenous vitamin C against metal reach malignant