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.
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