Iodine: Occurrence and Distribution

Overview of Iodine

Iodine (symbol I, atomic number 53) is an essential trace element for humans and animals, playing a crucial role in thyroid hormone synthesis. Its distribution varies significantly across the environment.

Sources in Marine Environments

The oceans are a primary reservoir. Seaweed, particularly brown algae (kelp), actively concentrates it from seawater. Marine animals, including fish and shellfish, accumulate it through their diet.

Terrestrial Distribution

Its presence in soil varies greatly depending on factors such as proximity to the ocean, geological history (past marine submersion), and soil type. Areas far from the sea or with a history of glaciation often exhibit soil deficiency.

Foods Containing Iodine

• Seafood: Fish (cod, tuna, haddock), shellfish (shrimp, oysters), and seaweed are excellent sources. The concentration varies depending on species and origin.
• Dairy Products: Milk, cheese, and yogurt can be significant contributors, particularly when livestock are fed supplements containing it, or when iodophor sanitizers are used in processing.
• Eggs: Found in the yolk, amount depends on the hen's diet.
• Iodized Salt: The most common source in many countries. Table salt is fortified with potassium iodide or potassium iodate.
• Plants: Concentration in vegetables and grains is dependent on the soil content in which they were grown.

Supplementation and Fortification

Dietary supplements containing potassium iodide or potassium iodate are available. Food fortification programs, primarily with iodized salt, are a public health strategy to prevent deficiency, particularly in regions with soil depletion.

Geological Factors

Regions with mountainous terrain or areas that experienced significant erosion may have lower soil levels. Goiters, an enlargement of the thyroid gland due to deficiency, were historically prevalent in such regions before widespread iodization programs.