Is chromium a trace essential metal?

If chromium is an essential metal it must have a specific role in an enzyme or cofactor, and a deficiency should produce a disease or impairment of function. To date, no chromium-containing glucose tolerance factor has been characterized, the purpose of the low-molecular-weight chromium-binding protein is questionable, and no direct interaction between chromium and insulin has been found. Furthermore, chromium³⁺ is treated like the toxic metals arsenic, cadmium, lead and mercury in animals. Chromium³⁺ may be involved in chromium⁶⁺-induced cancers because chromium⁶⁺ is converted to chromium³⁺ in vivo, and chromium³6+ is genotoxic and mutagenic. Although there is no direct evidence of chromium deficiencies in humans, dietary supplements exist to provide supraphysiological doses of absorbable chromium³⁺. Chromium³⁺ may act clinically by interfering with iron absorption, decreasing the high iron stores that are linked to diabetes and heart disease. If so, this would make chromium³⁺ a pharmacological agent, not an essential metal.