Possible toxicological aspects of megadoses of ascorbic acid (original) (raw)

Abstract

In recent years, ascorbic acid (vitamin C) in gram quantities has been claimed to have certain therapeutic effects in many pathological conditions which include pressure sores, common cold, atherosclerosis, bone pain and diabetes. In view of our limited knowledge of ascorbic acid metabolism, however, there has been some concern about possible adverse eff~ts of the regular and prolonged ingestion of large amounts of the vitamin. Large doses of ascorbic acid have been reported to result in gastro-intestinal disturbances in some individuals . It has also been reported that the urinary excretory level of oxalic acid, a metabolite of ascorbic acid [2,3], is elevated after a short course of the vitamin supplements . The increased degradation of ascorbic acid through oxalic acid pathways and the resulting decrease of the urinary pH could lead to formation of oxalate stones. There is, however, no substantial evidence that any of these possible side effects actually occur in humans. Some recent studies of the metabolism of ascorbic acid have suggested that an excess intake of the vitamin may lead to other side effects. Baker et al. have reported that ascorbic acid is in part metabolized to ascorbic acid sulphate, and in subsequent studies Houston and Levy have shown that if ascorbic acid and salicylamide are given together, the metal> olism of the latter through sulphate conjugation is inhibited. The present report describes the effect of megadoses of ascorbic acid in man on the urinary excretory levels of cysteine since the amino acid may act as a sulphate donor for the metabolism of the vitamin, and thiocyanate, the principal detoxication product of cyanide where cysteine is believed to be involved as a sulphate donor.

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