Iron edition · as at August 2026
How this amount comes about, which metal atom it hangs on and with what methods it is measured — traced through figures, dates and the one sentence the EU register provides for iron and oxygen.
Iron contributes to normal oxygen transport in the bodyUnder Regulation (EU) No 432/2012
In a healthy adult, one litre of arterial blood carries around 200 millilitres of oxygen. About three millilitres of that float freely in the plasma; everything else hangs on a protein of which a single red blood cell contains several hundred million copies. The difference between these two figures is why vertebrates have built a metal into their circulation instead of relying on mere solubility.
Aragonitterrasse compiles documents on individual minerals: measured values with a reference quantity, dates with a source, methods with a description. Only the wording the European Union has authorised for nutrition and health claims is quoted. Anything beyond that is descriptive text without legal effect and is marked as such.
For the pairing of iron and oxygen the Union Register contains exactly one wording. It appears in the box above, it appears again further down, and it appears in the documents in the same wording at every point. Paraphrases would be easier to read, but they would no longer be the authorised claim.
Each entry stands for a section of the detailed version. The order follows the path of the gas — from the amount, through the molecule, to the balance sheet of the metal.
Iron is present in an adult body in the order of three to five grams. The greater share of that sits not in stores but at work: bound in the blood cells that shuttle between lung and tissue. Chemically the element switches between two valencies, and it is precisely this switching that makes it usable for binding a gas — unlike elements with only one stable state.
For this relationship the Union Register carries a single wording. It belongs to iron alone and is not drawn together with any other mineral.
Iron contributes to normal oxygen transport in the bodyUnder Regulation (EU) No 432/2012
Gases dissolve in liquids according to a simple law: in proportion to the pressure they exert above them. At the pressures prevailing in the lung this gives about three millilitres per litre for oxygen in blood plasma. Reckoning with a resting turnover of around 250 millilitres of oxygen per minute, this dissolved share is arithmetically enough for a few seconds.
The way out is not to build up more pressure but to bind the gas chemically and release it again at the destination. A reversible bond raises the load per litre by more than sixtyfold without the partial pressure having to rise.
The transport protein of the red blood cell consists of four protein chains, two of each kind. Each chain encloses a flat organic disc with a single iron atom at its centre. Four chains, four discs, four metal atoms — and thus four loading places, occupied one after another.
The chains are not rigidly fastened together. They shift against one another by a few tenths of a nanometre as soon as the first place is occupied. Elucidating this mobility was a chapter of structural research in its own right and is dated further below.
From an intermediate of its own sugar breakdown the red blood cell makes a compound present at roughly the same concentration as the transport protein itself. It settles into a cavity between the two beta chains and from there influences how readily the gas is released again.
The cell thereby possesses a lever of its own that works independently of metal stock and cell count. Its share in the balance is set out in the documents with numerical values and time axes.
A red blood cell stays in circulation for around four months on average. It is then broken down, and the iron it contains is not lost: phagocytes in the spleen and liver release it from the ring molecule and pass it to a transport protein in blood plasma, which returns it to blood formation.
Around twenty milligrams circulate this way each day. Over the same period only one to two milligrams are added through food. The ratio of these two figures explains why the circulation of the metal is described in more detail in the specialist literature than its intake.
In 1937 a young chemist in Cambridge began to shine X-rays through crystals of the red blood pigment. For two decades the diffraction patterns could not be translated into a spatial arrangement, because one piece of information was missing: the phase of the scattered waves. Only in 1953 came the trick of building heavy metal atoms into the crystal lattice and calculating the missing quantity from the shift in the patterns. By 1959 a first spatial model existed; in 1962 the Nobel Prize in Chemistry followed.
From this work also comes the observation that on loading, the metal atom moves a few tenths of an angstrom into the plane of the ring disc and passes this tiny shift on to the whole chain. The connection between a movement on the picometre scale and the behaviour of an entire organ is one reason this molecule still appears in textbooks today.
Since the 1960s the content of the transport protein has been determined in the laboratory through a colour method. The sample is chemically converted into a uniform compound whose solution attenuates green light in a narrow wavelength range. From the attenuation measured, a fixed conversion factor gives the concentration in grams per decilitre. The method is regarded as the international reference method against which other instruments are calibrated.
Important when reading such values: the figure describes a concentration in a sample, not the amount of the metal in the whole body, nor the amount taken up from a meal. Three different questions, three different measured quantities — the documents keep them separate and name the reference quantity in each case.
Anyone moving to higher altitude breathes air with the same proportion of oxygen but at lower pressure. The organism responds on two time scales: the concentration of the sugar derivative mentioned in the red blood cell shifts within hours to a few days, whereas the number of blood cells themselves only changes over weeks. Physiological measurement series from mountain expeditions have documented both courses since the 1960s.
The authorised claim on iron makes no statement about such adaptations. It describes a recognised contribution, not a process under special conditions, and is reproduced in the documents at exactly that scope: Iron contributes to normal oxygen transport in the body
— Under Regulation (EU) No 432/2012.
This page shows five stations in short form; the documents set out each of them with the calculation, the reference quantity and the source, and add two tables as well as a questions section.
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