How Does Iodine Get Into Food? The Journey from Sea to Table

November 22, 2025 •

4 min read

An estimated one-third of the world's population is still at risk for iodine deficiency. Understanding how does iodine get into food is key to ensuring adequate intake of this crucial mineral for thyroid health, metabolism, and overall well-being. The journey of iodine to our plates involves both natural environmental processes and intentional human intervention.

Quick Summary

Iodine enters the food supply through natural absorption by marine life from oceans and fortification in products like table salt. This trace mineral also reaches land-based foods, such as dairy and produce, through fortified animal feed, sanitizing agents, and the iodine content of local soil.

Key Points

Ocean to Plate: Iodine is concentrated by marine life, such as seaweed and seafood, directly from seawater.
Soil Variation: The iodine content of fruits, vegetables, and crops varies significantly based on the local soil, with many inland areas being deficient.
Fortified Salt: The most widespread method of delivering iodine is through iodized table salt, a major public health success.
Animal Feed: Dairy products and eggs become reliable iodine sources when livestock and poultry receive iodine-fortified feed.
Fortification is Key: Fortification of salt, feed, and some commercial breads helps compensate for the low natural iodine levels in many land-based foods.
Global Efforts: Despite major progress, iodine deficiency remains a public health issue in many parts of the world with limited access to fortified foods or marine sources.

Natural Pathways: The Role of Oceans and Soil

The fundamental source of iodine on Earth is the ocean, where it exists in high concentrations. The mineral travels from the sea to inland areas through complex environmental processes, but its distribution on land is highly uneven. For centuries, rain and glaciation cycles have leached iodine from the topsoil in mountainous and flooded river valley regions, carrying it to the sea. Consequently, crops and grazing animals in these iodine-deficient inland areas tend to have very low iodine levels.

Marine Life as Natural Concentrators

Marine life is the most reliable natural dietary source of iodine. Fish, shellfish, and especially seaweed absorb and concentrate the mineral directly from the ocean water. This is why coastal populations historically had lower rates of iodine deficiency disorders compared to those living in mountainous regions, known as the "goiter belt". Seaweed, in particular, is an exceptionally concentrated source of iodine, with content varying greatly by species.

Soil Content and Agriculture

For land-based foods, the iodine content is a direct reflection of the soil in which it was grown. In iodine-rich coastal areas, fruits and vegetables can provide some iodine, but in vast inland regions with iodine-poor soil, produce is not a significant source. This has critical implications for regional diets, as reliance on locally grown produce in iodine-deficient areas can lead to widespread health issues.

Human Intervention: Fortification and Farming Practices

To combat widespread iodine deficiency, public health initiatives have implemented several strategies to add iodine to the food supply.

The Impact of Iodized Salt

One of the most successful public health measures in history is the addition of iodine to table salt, a practice that began in the 1920s in many countries. Today, iodized salt is a major dietary source for much of the world's population. Manufacturers voluntarily add iodine in the form of potassium iodide or potassium iodate to table salt. However, specialty salts like sea salt, kosher salt, and Himalayan salt are typically not iodized, and most processed foods are made with non-iodized salt. Consumers must check labels to ensure they are getting iodized salt.

Dairy Products and Fortified Feed

Dairy products, such as milk, yogurt, and cheese, have become a significant source of iodine in many diets. The iodine gets into these products primarily through supplements added to cattle feed. Additionally, iodine-containing sanitizing agents, or iodophors, used to clean milking equipment can also contribute to the iodine content of milk. This means the iodine levels in dairy can vary depending on farming practices and even seasonally.

Eggs and Commercial Food Processing

Eggs are another valuable source of dietary iodine, as the mineral is often added to hen feed to ensure adequate levels. The iodine is concentrated primarily in the egg yolk. Additionally, some commercially baked breads may contain iodine if manufacturers use iodate dough conditioners. This practice, however, is not as widespread as the iodization of salt, and the amount of iodine can vary considerably. Infant formulas are also commonly fortified with iodine.

The Journey to Your Plate: A Comparison

This table illustrates the primary ways iodine enters common foods, highlighting the differences between natural concentration and fortification.


Food Type	Primary Iodine Source	Consistency of Iodine Level	Dependence on Geography
Seafood (Cod, Shrimp)	Naturally concentrated from seawater.	Generally high and reliable.	Less dependent, but wild vs. farmed varies.
Seaweed (Kelp, Nori)	Naturally concentrated from seawater.	Highly variable by species and origin.	Less dependent.
Dairy Products	Fortified animal feed, iodophor sanitizers.	Moderate, varies by farm and season.	Not dependent on local soil.
Eggs	Fortified hen feed.	Variable, depends on feed.	Not dependent on local soil.
Crops (Fruits/Vegetables)	Natural absorption from soil.	Highly variable, often low.	Heavily dependent on local soil.
Iodized Table Salt	Intentional fortification.	High and consistent.	Not dependent on local soil.

Conclusion: Navigating a Diverse Iodine Landscape

In conclusion, iodine enters our food supply through a combination of natural pathways and human intervention. Natural sources, like seafood and seaweed, absorb iodine directly from the ocean, while the mineral's presence in land-based crops is dictated by the iodine content of the soil, which is often deficient in many regions. To ensure sufficient intake, public health measures have relied on fortifying staples like table salt, which has significantly reduced iodine deficiency globally. Today, dairy and eggs also provide reliable iodine through fortified animal feed. For individuals, consuming a diverse diet that includes marine products and using iodized salt is a simple and effective strategy to maintain adequate iodine levels. For more information on dietary sources of iodine, refer to the National Institutes of Health Fact Sheet for Consumers.

Frequently Asked Questions

No, most sea salt contains only trace amounts of iodine and is not a reliable source. It is best to use salt that is specifically labeled 'iodized' if you rely on it for your iodine intake.

Yes, vegans and vegetarians are at a higher risk of iodine deficiency because they exclude major dietary sources like seafood, dairy, and eggs. They must ensure adequate intake through iodized salt or supplementation.

Iodine is present in the Earth's crust but is easily leached away by water, such as through glaciation or flooding. Coastal areas tend to retain more iodine, while mountainous regions and river valleys often have low-iodine soil.

The amount of iodine lost during cooking can vary, but studies show that some iodine can be lost, especially with certain cooking methods. It is still important to consume a variety of iodine-rich foods, both cooked and raw.

Food manufacturers in the U.S. typically use non-iodized salt in processed foods. If iodized salt is used, it must be declared in the ingredients list on the food label.

No, the iodine content of seaweed can vary dramatically depending on the species and where it was grown. For example, kelp typically contains significantly more iodine than nori.

Yes, trace amounts of iodine can be found in drinking water, as it is carried by rain from the ocean back to the earth. However, the levels are generally low and inconsistent.