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Vitamins and Vitamin DeficienciesWater Soluble Vitamins Vitamin C. Vitamin C (ascorbic acid) is involved in collagen metabolism, and is thus a necessary cofactor for adequate wound healing. Its effects on immune function include improved polymorphonuclear cell adherence, delivery and motility, increased antibody production, and enhanced lymphoproliferative responses. Vitamin C is an important component of oxidation reduction and hydrogen ion transfer reactions, as well as a powerful antioxidant. Folic acid. Folic acid deficiency may result in megaloblastic anemia after as little as 4 weeks without multivitamin supplementation. Folic acid is a cofactor in numerous metabolic pathways, especially those of amino acid and nucleotide metabolism, and is necessary for DNA synthesis. Folic acid deficiency has been shown to be related to certain birth defects, especially anencephaly. Niacin. Niacin (nicotinic acid, vitamin B3) deficiency can result in pellagra, which is characterized by dermatitis, diarrhea, and dementia. Niacin is an important component of nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), cofactors of dehydrogenase enzymes involved in many important metabolic pathways.' Thiamine. A deficiency of thiamine (vitamin‑B‑1) can develop quite rapidly. This is often manifested with symptoms characteristic of peripheral neuritis, known as "dry beriberi." In severe cases, cardiac dysfunction from high‑output failure can occur, and is referred to as "wet beriberi." The occurrence of severe, sometimes fatal, clinical thiamine deficiency in patients receiving TPN` demonstrates the need to insure that all parenteral nutrition contain thiamine in adequate quantities. Thiamine may be deficient in apparently well nourished alcoholics." Immediate, appropriate, and daily multivitamin supplementation is especially important in these patients. Severe alcoholism is the most common factor predisposing to the development of Wernicke's encephalopathy.' The need for thiamine increases as carbohydrate intake increases." Thiamine is a cofactor in various metabolic reactions. It also plays a role in nerve transmission! Riboflavin. Riboflavin (vitamin B2 deficiency is characterized by stomatitis, glossitis, and seborrheic dermatitis. Riboflavin is an important component of flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), cofactors of enzymes involved in biological oxidation‑reduction reactions, including those involved in glucose oxidation, amino acid deamination, and free fatty acid breakdown.' Vitamin B6. Vitamin B6 (pyridoxine) is required for amino acid metabolism and protein synthesis. Transamination and decarboxylation are essential biochemical processes that require vitamin B6 or its metabolites.' Metabolites of vitamin B6 are involved in the biosynthesis of porphyrins and heme. Deficiency of pyridoxine produces glossitis and stomatitis. Peripheral neuritis and seizures can also occur. Vitamin B12. Deficiency of vitamin B12 (cyanocobalamin) can result in pernicious anemia. Vitamin B12 is essential for thymidylate synthesis and, therefore, for DNA synthesis. Any abnormality of the distal ileum, where its metabolic receptor is found, can reduce vitamin B12 absorption. Pantothenic acid. Clinical signs of pantothenic acid deficiency include nausea, vomiting, headache, muscle cramps, fatigue, and paresthesia of the hands and feet. Pantothenic acid is used as a building block in the synthesis of coenzyme A (essential for glucose, protein, and fat metabolism) and acyl carrier protein (essential for fatty acid synthesis). Biotin. Biotin deficiency may result in dermatitis, as well as in paresthesia. Biotin is an important cofactor for many enzymes involved in carbohydrate, fat, and protein metabolism.' Fat Soluble Vitamins Vitamin A. Vitamin A has numerous functions. Besides its well‑known role in vision, it is important for cellular differentiation and for the functioning of the immune systems. Vitamin A has effects on cell‑mediated immunity and lymphoproliferation in vitro. A correlation exists between vitamin A deficiency and an increased susceptibility to infections. Vitamin A may also reverse the inhibitory effect of corticosteroids on the healing of intestinal anastomoses. Vitamin D. The major function of vitamin D is maintenance of plasma calcium and phosphate homeostasis.' Vitamin D deficiency results in inadequate intestinal absorption and renal reabsorption of calcium and phosphorus and hyperparathyroidism. Laboratory findings include low levels of calcium and phosphorus, and increased serum alkaline phosphatase activity' Vitamin E. Vitamin E (tocopherol) is an antioxidant and protects cell membranes from the deleterious effects of the products of fat oxidation. Vitamin E is derived from a series of dietary tocopherols and tocotrienols, the most potent of which is D‑alpha‑tocopherol. Vitamin K. Commercially prepared adult vitamin solutions do not contain vitamin K because it may interfere with anticoagulation therapy. The long‑term TPN patient may require weekly injections of vitamin K. |
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