Key vitamins and trace elements in the critically ill.

Trace elements and vitamins are essential components of nutrition (unless specified, vitamins and trace elements will hereafter be designated globally as micronutrients). Trace elements are metals and metalloids present in the body at fairly constant concentrations. Trace elements act as a structure of enzymes or as cofactors, and frequently they exert electron transfer functions. Their absence causes reproducible structural or biochemical deficits, and they are associated with specific biochemical alterations. These alterations can be prevented or corrected by the intake of the deficient element alone. Vitamins are organic substances required in minute amounts, and they are not synthesized by the body (or not in sufficient quantities). Vitamins are cofactors in the different metabolic steps of enzymes, carbohydrate, protein, and lipid metabolism. Micronutrients are involved in the prevention of nutritional deficiencies, immune humoral and cellular defense, regulation of gene expression during the acute phase response, antioxidant defense, and prevention of chronic diseases. Most micronutrients have been discovered due to acute nutritional deficiencies causing specific diseases, such as ascorbic acid and scurvies, zinc and delayed wound healing and dwarfism, selenium and skeletal myopathy, and iron and anemia. Micronutrient deficiency in the general population is infrequent, but inadequate intake is widespread as shown by a series of epidemiological studies carried out over the last 2 decades [1–3]. Due to changes in nutrient