Chromium has long been thought to be an essential trace element. However, evidence has begun to emerge that Cr^III may not be essential and might actually pose health risks.

The assumed essential biological role of Cr^III has led to the hypothesis that this species is actively taken up by transferrin (Tf), which normally mediates Fe^II uptake in the body. Peter Lay and colleagues, University of Sydney, Australia, used a combination of bio-layer interferometry, which measures biomolecular interactions, and uptake studies in cultured human liver cells to test this hypothesis.

The researchers found that Cr^III indeed binds efficiently to Tf, however, this disrupts the Tf cycle. Thus, binding to Tf does not facilitate Cr^III uptake, but blocks it instead. These results provide further evidence for Cr^III being nonessential, since absorbed dietary Cr^III would likely bind to Tf in the blood and never be transported into cells. Tf binding may even be a protective mechanism against Cr^III toxicity.

Since Cr^III is commonly added to dietary supplements, the question of whether it is essential or simply toxic is a crucial one, and this study adds an important piece to the puzzle.

• Binding of Chromium(III) to Transferrin Could be Involved in Detoxification of Dietary Chromium(III) Rather Than Transport of an Essential Trace Element,
  Aviva Levina, T. H. Nguyen Pham, Peter A. Lay,
  Angew. Chem. Int. Ed. 2016.
  DOI: 10.1002/anie.201602996