On the antioxidant effects of ascorbic acid and glutathione

Abstract

Ascorbic acid (vitamin C) is required in the diets of humans, certain other primates, guinea pigs and several other species [l-5]. These animals, in contrast to most others, do not have the ability to synthesize ascorbic acid from glucose because they lack the enzyme L-gulonolactone oxidase, which is required for the formation of 2-keto-L-gulonolactone; this compound is spontaneously converted to ascorbic acid. Ascorbic acid deficiency leads to scurvy, which can be prevented in humans by administration of as little as 10mg of ascorbic acid per day [6]. Many have thought that larger doses of ascorbic acid might be beneficial for health [3,7]. Szent-Gybrgyi, soon after his pioneering research on ascorbic acid, considered the idea that it might have a useful role in the therapy of infections. Ascorbic acid has been claimed to be effective in the prevention and treatment of cancer [7-lo], the common cold [ 11,121, atherosclerosis [3,13,14], cataracts [15] and AIDS [16]. It has been claimed that increased intake of ascorbic acid has favorable effects on the immune system, healing of wounds, various types of stress including those due to physical exertion, cigarette smoking, and extremes of temperature, allergic responses, and mental health problems. These subjects have been reviewed [3,7,15,17,18]. In general, each of these claims has been contradicted, at least to some degree, by subsequent studies and the literature continues to reflect controversy apparently because it has not yet been possible to obtain reproducible objective evidence. A claim that a particular drug or treatment can cure a wide variety of conditions, perhaps everything from housemaid’s knee to tuberculosis, is typically viewed with skepticism. So too might one be justifiably dubious about a theory according to which a wide variety of diseases are produced by oxidative phenomena and free radicals. Nevertheless, if such a theory is even partially valid, beneficial effects might be expected after administration of compounds such as ascorbic acid which has potent reducing properties and which is highly reactive. In contrast to the claims made for large doses of ascorbic acid, there can be no doubt but that very small doses of ascorbic acid are sufficient to prevent scurvy; this has been observed frequently. Perhaps ascorbic acid performs a specific function that