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Vitamins and herbal preparations, particularly those sold in health food stores, are considered by many to be innocuous but may have potential toxicity, especially when taken in excessive amounts over a period of time. Also, herbal preparations may contain toxic contaminants that can cause poisoning.


Hypervitaminosis from the fat-soluble vitamins A, D, E, and K can produce subacute toxicity (after days to a few weeks) or chronic toxicity (after weeks to months of excessive ingestion). Of the water-soluble vitamins, niacin, pyridoxine, and ascorbate are associated with toxicity (Table 205-1).

TABLE 205-1Clinical Features of Hypervitaminosis


Dietary vitamin A is present in two forms: preformed vitamin A (retinol and retinyl palmitate [an ester] from animal sources) and provitamin A (carotenoids) found in plants. After ingestion, the ester form is hydrolyzed in the GI tract to retinol. Retinol is then absorbed into intestinal mucosal cells, where it then combines with a fatty acid to again become a retinyl ester. Carotenoids are dark-colored compounds found in plants. β-Carotene is the carotenoid most efficiently converted to retinol by duodenal mucosal cells. The recommended daily allowance (RDA) for preformed vitamin A (retinol) is 900 micrograms (3000 IU) for adolescents and adult men, and 700 micrograms (2400 IU) ...

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