Scientific facts about two minerals — per Regulation (EU) No 432/2012
View the Data SheetBoth elements in this issue belong to the same subject area, yet they have no shared location in the body. Zinc appears here as a component of an ordered storage assembly in the pancreas, chromium as cargo carried by a protein traveling through blood plasma. The following sections trace each location separately.
One distinction up front runs through the whole text: the structural and transport chemistry referenced here comes from the scientific literature and is editorial factual content. What may be quoted verbatim under Regulation (EU) No 432/2012 is two lines; they appear further below, each set apart in its own frame.
In the storage granules of the pancreas's beta cells, the hormone produced there is not present as a single molecule but as a group of six. Three pairs arrange around a threefold rotational axis; on this axis sit two zinc ions, each held by three histidine side chains from three different molecules. This arrangement has been described by X-ray crystallography since the 1970s, and in electron micrographs the granule contents accordingly appear as a dense, regularly ordered core.
The assembly holds together only as long as its surroundings stay confined. Once the contents leave the granule, the concentration drops by several orders of magnitude, the group of six breaks apart into individual molecules, and both ions detach along with it. The metal itself is not converted in this process: it holds a geometry together for as long as it exists, and is released again along with it.
That is structural chemistry and nothing more. No statement permitted under Regulation (EU) No 432/2012 follows from this information.
For the ion to reach the granule at all, it must cross a membrane. Responsible for this is a transport protein that the genetics literature lists under the designation SLC30A8 and the protein literature calls ZnT8. Both names refer to the same molecule; the double naming comes from two separate classification systems, not from two different findings.
The transporter works as an exchanger: it carries the metal ion into the granule and releases protons to the outside in return. This exchange is driven by the acidic environment inside the granule, which a dedicated pump maintains. Without this gradient, the interior never reaches the concentration at which the ordered assembly can form in the first place.
After absorption in the small intestine, chromium is not present in plasma as a free ion. It binds to transferrin, the two-lobed protein whose two metal sites are described primarily for trivalent iron. Each site — one in the N-lobe, one in the C-lobe — holds the ion via two tyrosine residues, one histidine, and one aspartate, with a carbonate ion joining as a counterpart.
Trivalent chromium occupies exactly these pockets and thus competes with the far more abundant iron. At the cell surface, the transferrin receptor takes up the loaded protein; in the acidified endosome the binding loosens, the ion is released, and the emptied protein returns to the surface. The pathway is thus the same one physiology has long described for iron.
None of these three sections allows any conclusion about an individual person's condition. They describe molecular structure and transport pathways, not findings.
The European Commission maintains a separate entry for zinc and for chromium. Both appear here unchanged and are not merged into a single combined statement.
Zinc has atomic number 30 and is practically never found unbound in the body. The scientific literature distinguishes sites inside enzymes, where the ion takes part in a reaction, from purely structural sites, where it holds a fold together.
This issue follows a third case: the ion as a link between six identical hormone molecules in the pancreas's storage granule. The reference value for nutrition labeling is ten milligrams per day; oysters, wheat germ, pumpkin seeds, and beef top the content tables.
Per Regulation (EU) No 432/2012
In food, chromium is present in its trivalent form. The hexavalent form belongs to a different context and does not appear in this issue. In plasma, the trivalent ion travels coupled to a transport protein, not in solution. The labeling reference value is 40 micrograms per day.
Per Regulation (EU) No 432/2012
Neither entry implies an intake amount, a timing, or any statement about an individual person's condition. Neither line references disease, whether explicitly or by implication.
They may be printed only on products that provide at least fifteen percent of the respective reference value per serving or per hundred grams. Anyone below that threshold prints nothing at all — analytical detectability alone is not enough.
Then the fully written-out version is available as a PDF file: the coordination geometry of both metal sites with a figure, the binding constants from the referenced scientific literature, both content tables in full including the range for each product group, and a source line with year and citation for every section.
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