Iodine is the heaviest of the stable halogens and is remarkably scarce in the Earth's crust. Common estimates are in the range of a few tenths of a milligram per kilogram of rock — an order of magnitude that makes the element look like a footnote in standard geology references. In seawater the concentration is several orders of magnitude higher, and this very difference still shapes the makeup of what ends up on dinner tables in Central Europe today.
The reason lies in recent geological history. In regions that lay under ice during the glacial periods or were flushed by meltwater, the original topsoil was stripped away. The soils that formed afterward are replenished mainly through precipitation, and that input is slow. The Alps, the central European uplands and large parts of inland Eastern Europe are therefore considered areas with low soil levels in the specialist literature — while coastal regions regularly show higher levels.
This starting point creates a practical difficulty: composition tables for one and the same food differ considerably depending on the country of origin. Aegirinweg gathers what can be documented on this — and draws a clear line between descriptive information on composition and the one sentence the European Union has authorized for this element.
Element 53 · Editorial Outline
Three ways into a trace element you can neither see nor taste: where it comes from, which methods are used to quantify it and which single wording about it is permitted in the European Union.
Go to the outlineThe following sections stand on their own. They do not build on each other and can be read in any order.
The total amount in an adult's body is usually given as 10 to 20 milligrams — an amount that would fit on a match head. That is why intake is calculated in micrograms, not milligrams. For the area of energy metabolism, the EU list contains a single wording for this element, reproduced here unchanged:
Per Regulation (EU) No 432/2012
The Parisian saltpeter maker Bernard Courtois worked with seaweed ash to obtain potassium compounds for making gunpowder. When he added sulfuric acid to the residue, a violet vapor rose and settled on cold surfaces as shiny, metallic crystals. A few years later, Joseph Louis Gay-Lussac gave the substance the name that refers to the color of the vapor.
Industrial production still depends on two very different types of deposits. In the Atacama, iodate is obtained as a by-product of mining caliche rock, which was originally developed for its sodium nitrate. In Japan, most of it comes from brines extracted together with natural gas from sedimentary layers. Together, these two sources account for the vast majority of world production.
In 1922, the Swiss canton of Appenzell Ausserrhoden became the first administrative unit in Europe to supply its population with table salt containing this element. In the United States, the state of Michigan followed two years later. The principle — using a staple food eaten daily as a carrier — was later adopted by numerous countries and remains a voluntary option in Germany to this day.
Between its occurrence in nature and the number on a package lie several calculation steps, each following its own rules. Anyone who wants to interpret a figure on a label correctly should know which of these steps it represents.
For nutrition labeling, Annex XIII of Regulation (EU) No 1169/2011 sets a reference value of 150 micrograms per day. This value makes it possible to calculate percentages on packaging in a uniform way. It is expressly not an individual requirement and says nothing about any particular person's situation. Scientific bodies also publish their own estimated and guideline values, which may differ by country and age group.
An authorized claim may not appear on just any product. Regulation (EC) No 1924/2006 makes its use conditional on the food containing a significant amount of the nutrient concerned — usually at least fifteen percent of the reference value per serving or per hundred grams. Here that works out to a little over 22 micrograms. Products below that level may not carry the sentence, no matter how accurate it would be in content.
Iodine contributes to normal energy-yielding metabolism. In line with Regulation (EU) No 432/2012. The term energy metabolism refers to all the biochemical conversions through which the body uses energy sources from food. The wording is aimed at the general population, describes a state rather than an effect in an individual case, and makes no statement about diseases, their course or how to avoid them. Anything beyond that is marked on this page as editorial text.
The full version expands on the points outlined here: the study of deposits, the chronology of salt iodization from 1922 to today's legal situation, an annotated overview of content levels and the sources for every regulation quoted.
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