Chromium as an essential nutrient: a review

Chromium (Cr) has been studied since the end of the 19 th century, when carcinogenic effects of hexavalent Cr were discovered. Essentiality of trivalent Cr was demonstrated in 1959; Cr 3+ has been studied in humans and laboratory animals since the 1970s and it is only since the 1990s that Cr has been studied as an essen- tial element in livestock animals with the same intensity. Trivalent chromium is essential to normal carbohydrate, lipid and protein metabolism. Chromium is biologically active as part of an oligopeptide - chromodulin - poten- tiating the effect of insulin by facilitating insulin binding to receptors at the cell surface. With chromium acting as a cofactor of insulin, Cr activity in the organism is parallel to insulin functions. Cr absorption is low, ranging between 0.4 and 2.0% for inorganic compounds while the availability of organic Cr is more than 10 times higher. Absorbed Cr circulates in blood bound to the β-globulin plasma fraction and is transported to tissues bound to transferrin. Absorbed Cr is excreted primarily in urine, by glomerular filtration; a small amount is excreted through perspiration, bile and in milk. The demand for Cr has been growing as a result of factors commonly referred to as stressors, especially during different forms of nutritional, metabolic and physical strain. This review describes Cr metabolism, the different biological functions of Cr and symptoms of Cr deficiency.