Jerry M. Rivers

Safety of High-level Vitamin C Ingestion

: Reports suggesting that gram doses of ascorbic acid are beneficial for the prevention and treatment of several disorders have led to widespread ingestion of vitamin C supplements. Possible adverse health effects of this practice have, therefore, received considerable scrutiny. Of major concern has been the influence of ingesting gram amounts of ascorbic acid on renal calcium oxalate stones, systemic conditioning, uricosuria, vitamin B12 destruction, mutagenicity, and iron overload. Despite contradictory reports, the consensus from an extensive literature is that these adverse health effects are not induced in healthy persons by ingesting large doses of ascorbic acid. Possible interactions of ascorbic acid with other nutrients and physiological processes may be of importance to human health and, therefore, merit further research. The ingestion of large doses of ascorbic acid is contraindicated in cases of renal insufficiency, chronic hemodialysis patients, unusual forms of iron overload, and oxalate stoneformers.

RELATIONSHIPS OF ASCORBIC ACID TO PREGNANCY, AND ORAL CONTRACEPTIVE STEROIDS*

The 1974 RDA is 60 mg per day for pregnant women and 80 mg per day for lactating women. In the present study an attempt was made to simulate this intake in the guinea pig and study reproduction performance in relation to guinea pigs fed chronically low and high levels. In animals that conceived and carried the young to term, all 3 dietary levels of ascorbic acid appeared to be adequate for maintaining viability of fetuses and of offspring, and for growth of offspring during the nursing period. The chronically low intake level was not adequate for growth after weaning. The control group was superior to the chronically low-intake group but inferior to the high-intake group in conceiving, producing litters, and carrying litters to term. The level of intake in the control group was inadequate to maintain tissue stores. Even the high intake was inadequate to maintain some tissues at saturation levels. The results suggest that the requirement for ascorbic acid during pregnancy and lactation has been markedly underestimated.

Dietary ascorbic acid and hepatic mixed function oxidase activity in the guinea pig

Studies were carried out to characterize the response of hepatic mixed function oxidase (MFO) activity to chronic ascorbic acid deficiency and excessive ascorbic acid intake in the guinea pig. When guinea pigs were fed excessive ascorbic acid, there was a small increase in hepatic cytochrome P-450 which was unaccompanied by any alteration in drug-metabolizing enzyme activity. Similarly, induction of MFO activity by phenobarbital was not modified by excessive ascorbic acid administration. Chronic ascorbic acid deficiency resulted in depressed metabolism of aniline, aminopyrine, ethoxycoumarin and benzphetamine, but not of ethylmorphine, in comparison with animals fed diets containing control and/or excessive amounts of ascorbic acid. In contrast to the metabolism of all drugs studied, the 7 alpha-hydroxylation of cholesterol was depressed by both inadequate and excessive vitamin C intake, demonstrating the unique sensitivity of cholesterol 7 alpha-hydroxylase to dietary ascorbate.

Ascorbic acid catabolism by gut microflora: studies in germ-free and conventional guinea pigs

Abstract The role of gut microflora in ascorbic acid catabolism was investigated in both conventional and germ-free guinea pigs. In vitro studies demonstrated extensive degradation of the vitamin by fresh feces, cecal, and colonic contents of conventional guinea pigs. Direct injection of [1- 14 C] ascorbic acid into the cecum of conventional guinea pigs in vivo yielded a 70% recovery of the label as respiratory 14 CO 2 within 6 hr compared with only 5% recovery following injection into the virtually sterile peritoneum in a comparable group of conventional guinea pigs. Thus, ascorbic acid not absorbed prior to reaching the lower gastrointestinal tract stands to be extensively decarboxylated by microflora in the cecum. In a companion study of germ-free guinea pigs, 10% of an administered dose of [1- 14 C] ascorbic acid was expired as 14 CO 2 within 36 hr post-injection following intraperitoneal injection compared with 16% recovery in a matched group of conventional animals injected at the same site. Results of this series of studies suggest that hepatic decarboxylation and gut microflora, in tandem, contribute to ascorbic acid decarboxylation in this species.