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, chromium(3+) is treated like the toxic metals arsenic, cadmium, lead and mercury in animals. Chromium(3+) may be involved in chromium(6+)-induced cancers because chromium(6+) is converted to chromium(3+) in vivo, and chromium(3+) is genotoxic and mutagenic. Although there is no direct evidence of chromium deficiencies in humans, dietary supplements exist to provide supraphysiological doses of absorbable chromium(3+). Chromium(3+) 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 chromium(3+) a pharmacological agent, not an essential metal.