Vitamins are essential for normal human growth and development.43 By definition, a vitamin is a substance that is present in small amounts in natural foods, is necessary for normal metabolism, and whose lack in the diet causes a deficiency disease.37 According to the American Medical Association, healthy men and nonpregnant women who eat a varied diet do not need supplemental vitamins.8 In a recent national survey, 73% of adults in the United States reported use of a dietary supplement within the past year.202 Eighty-five percent of these supplement users reported use of a multivitamin-multimineral. Many of these individuals share the mistaken beliefs that vitamin preparations provide extra energy or promote muscle growth and regularly ingest quantities of vitamins in great excess of the recommended dietary allowances (RDAs) (Table 41–1). Some vitamins are associated with consequential adverse effects when ingested in very large doses.
Table 41–1. Recommended Dietary Daily Allowances/Adequate Daily Intakes* |Favorite Table|Download (.pdf)
Table 41–1. Recommended Dietary Daily Allowances/Adequate Daily Intakes*
|Age (yr)||Vitamin A (μg RE/IU)||Vitamin D (μg/IU)||Vitamin E (mg α-TE/IU)||Vitamin C (mg)||Vitamin B6 (mg)||Niacin (mg NE)|
Vitamins can be divided into two general classes. Most of the vitamins in the water-soluble class have minimal toxicity because they are stored to only a limited extent in the body. Thiamine, riboflavin, cyanocobalamin, pantothenic acid, folic acid, and biotin are not reported to cause any toxicity following oral ingestion.43 Ascorbic acid (vitamin C), nicotinic acid (vitamin B3), and pyridoxine (vitamin B6) are associated with toxicity syndromes. The fat-soluble vitamins, however, can bioaccumulate to massive degrees. ...