Possible toxicological aspects of megadoses of ascorbic acid (original) (raw)
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Ascorbic acid absorption in humans: A comparison among several dosage forms
Journal of Pharmaceutical Sciences, 1982
There have been few studies conducted to determine the efficiency of ascorbic acid absorption in humans. Differences in the extent of its absorption among individuals may contribute to the outcome of clinical trials. Ascorbic acid absorption in four subjects was investigated from several oral dosage forms containing 1 g of the vitamin (solution, tablet, chewable tablet, and timed-release capsule). Approximately 85% of an intravenous dose was recovered in the urine as ascorbic acid and its major metabolites. In contrast, only -30% of the dose was recovered from the solution and tablet forms. A considerably smaller fraction of the dose (-14%) was recovered from the timed-release capsule. There was considerable intersubject variation in ascorbic acid absorption and there appeared to be good and poor absorbers of the vitamin. Consideration should be given to the influence of the extent of ascorbic acid absorption on the results of clinical trials.
Ascorbic acid absorption in man: influence of divided dose and food
Life Sciences, 1981
The urinary recovery of ascorblc acid (AA) was examined in 3 subjects when the vitamin was given as a single I g dose in solution (control), as divided doses in solution (0.125 g every 15 rain. for g doses) and as a I g solution after eating a meal high in fat content. The divided dose and after-meal treatments produced a significant increase in AA absorption compared to the corresponding control experiment, 7296 and 6996 increase, respec'~ively. Absorption appears to be delayed and prolonged under the latter conditions. These results are consistent with the suggestion that the vitamin is absorbed by a specialized process at sites high in the small intestine.
The biochemical, physiological and therapeutic roles of ascorbic acid
African Journal of Biotechnology, 2010
Ascorbic acid is an important micronutrient necessary for a significant number of metabolic reactions in humans and other primates. It is a strong reducing agent involved in reduction reaction and it is structurally related to glucose. Experimental and epidemiological studies have documented the biochemical, physiological and therapeutic roles of ascorbic acid. It is an essential water-soluble antioxidant vitamin derived from exogenous source; thus its role in human health is worthy to be considered particularly because of the current global economic trend. The biochemical, physiological and therapeutic roles of ascorbic acid is reviewed, providing further insights into the role of ascorbic acid in biological functions.
Mini-Reviews in Medicinal Chemistry, 2012
Ascorbic acid is a low molecular weight antioxidant well known as anti-scorbut acting vitamin C in humans, primates and guinea pigs. This review summarizes basic data about ascorbic acid in its physiological action point of view. It is divided into biochemistry of ascorbic acid synthesis, mechanism of antioxidant action and participation in anabolism, pharmacokinetics and excretion, exogenous ascorbic acid immunomodulatory effect and participation in infectious diseases, impact on irradiation and intoxication pathogenesis, and supplementary demands. The primary intention was to consider ascorbic acid not only as an antioxidant but also as a chemical compound affecting multiple pathways with a potential beneficial impact in many diseases and processes in human body.
Clinical chemistry, 1992
Examination of 4379 routine urinalysis specimens with dipsticks sensitive to ascorbic acid showed that 22.8% were positive specimens. The mean urinary vitamin C concentration in this population was 2120 mumol/L. There was a high rate of false-negative dipstick results for hemoglobin in patients with vitamin C in the urine. The highest false-negative rates were observed in urine samples containing less than 50 erythrocytes per high-power field. In further experiments when volunteers consumed supplemental oral USP vitamin C at doses of 100, 250, 500, and 1000 mg or vitamin C-containing fruit juices, even the lowest doses of oral vitamin C or juice resulted in sufficient urinary vitamin C to produce false-negative dipstick results in hemoglobin and glucose testing. To prevent potentially dangerous false-negative results, screening urinalysis protocols relying only on dipstick testing should include a check for urinary vitamin C or use a dipstick that is not subject to vitamin C interfe...
Role of Vitamin C (Ascorbic Acid) on Human Health- a Review
Vitamin C, also known as ascorbic acid, abounds in nature and is highly labile. It is a water-soluble vitamin that is lost in large amounts during food processing. It is a vitamin whose prescribed requirement across cultures is not uniform. For example , the prescribed requirement of vitamin C in Great Britain is 30mg/day, while in the U.S.A., it is 60mg/day and 100mg/day in Japan. These variations are unusual and point to the need for further research to establish the acceptable RDAs for diverse populations. The RDA for vitamin C should be more than the amount needed to prevent the occurrence of disease. Vitamin C plays significant functions in the body that enhance its role in the health status of the human body. The biochemical functions of vitamin C include: stimulation of certain enzymes, collagen biosynthesis, hormonal activation, antioxidant, detoxification of histamine, phagocytic functions of leukocytes, formation of nitrosamine, and proline hydroxylation amongst others. Th...
Evaluation of Pharmacologically Interesting Dose Range of Ascorbic Acid in Mice
Objective: Ascorbic acid is the most abundant water-soluble naturally occurring organic compound with antioxidant properties. It serves as a cofactor for enzymes involved in hormone biosynthesis, and the regeneration of antioxidants. Plants and food rich in ascorbic acid have been widely used in Ayurveda to treat a variety of psychologically stress related disorders.
Oxalic acid excretion after intravenous ascorbic acid administration
Metabolism, 2009
Ascorbic acid is frequently administered intravenously by alternative health practitioners and, occasionally, by mainstream physicians. Intravenous administration can greatly increase the amount of ascorbic acid that reaches the circulation, potentially increasing the risk of oxalate crystallization in the urinary space. To investigate this possibility, we developed gas chromatography mass spectrometry methodology and sampling and storage procedures for oxalic acid analysis without interference from ascorbic acid and measured urinary oxalic acid excretion in people administered intravenous ascorbic acid in doses ranging from 0.2 to 1.5 g/kg body weight. In vitro oxidation of ascorbic acid to oxalic acid did not occur when urine samples were brought immediately to pH less than 2 and stored at −30°C within 6 hours. Even very high ascorbic acid concentrations did not interfere with the analysis when oxalic acid extraction was carried out at pH 1. As measured during and over the 6 hours after ascorbic acid infusions, urinary oxalic acid excretion increased with increasing doses, reaching approximately 80 mg at a dose of approximately 100 g. We conclude that, when studied using correct procedures for sample handling, storage, and analysis, less than 0.5% of a very large intravenous dose of ascorbic acid is recovered as urinary oxalic acid in people with normal renal function.
AN OVERVIEW OF ASCORBIC ACID BIOCHEMISTRY ASKORBĐK ASĐT BĐYOKĐMYASINA BĐR BAKIŞ
Ascorbic acid is a cofactor for several enzymes participating in the post-translational hydroxylation of collagen, in the biosynthesis of carnitine, in the conversion of the neurotransmitter dopamine to norepinephrine, in peptide amidation and in tyrosine metabolism. In addition, vitamin C is an important regulator of iron uptake, It reduces ferric Fe 3+ to ferrous Fe 2+ ions, thus promoting dietary non-haem iron absorption from the gastrointestinal tract, and stabilizes iron-binding proteins. Most animals are able to synthesise vitamin C from glucose, but humans, other primates, guinea pigs and fruit bats lack the last enzyme involved in the synthesis of vitamin C (gulonolactone oxidase) and so require the presence of the vitamin in their diet. Thus the prolonged deprivation of vitamin C generates defects in the post-translational modification of collagen that cause scurvy and eventually death. In addition to its antiscorbutic action, vitamin C is a potent reducing agent and scavenger of free radicals in biological systems.