Which foods contain high levels of iodine?

December 26, 2025 •

4 min read

According to the World Health Organization, iodine deficiency is the world's most preventable cause of brain damage and intellectual disability. The human body cannot produce iodine, making dietary intake essential for producing thyroid hormones that regulate metabolism and growth. Excellent sources are primarily marine foods, dairy, and iodized salt, but content can vary regionally.

Quick Summary

This guide details primary dietary sources of iodine, including marine life, dairy, and fortified products. It examines specific examples like seaweed, cod, and eggs, and addresses considerations for vegans and vegetarians. The article also provides a comparison of iodine content and highlights the importance of this mineral for overall health.

Key Points

Seaweed is the richest natural source: Varieties like kelp, wakame, and nori contain exceptionally high and variable levels of iodine.
Marine life is a primary source: Seafood such as cod, shrimp, and oysters absorb iodine from the ocean, making them excellent dietary options.
Dairy products are reliable: Milk, yogurt, and cheese are significant sources of iodine in many diets, primarily due to livestock supplementation.
Iodized salt is widely used for fortification: Adding iodine to table salt is a common and effective public health strategy to prevent deficiency.
Vegans and vegetarians need planning: Without seafood or dairy, plant-based diets require attention to fortified foods, moderate seaweed, or supplementation to ensure sufficient intake.
Content varies geographically: The iodine level in plant and animal foods depends on the mineral content of the local soil and water.
Essential for thyroid function: Iodine is critical for producing thyroid hormones that regulate metabolism, development, and numerous bodily functions.
Deficiency risks are significant: Insufficient iodine can cause goiter and, most seriously, impair fetal and infant neurological development.
Excess can also be harmful: Consuming too much iodine, often from overusing kelp supplements, can also lead to thyroid problems.

Why is Iodine So Important for Your Health?

Iodine is a crucial mineral for the proper functioning of the thyroid gland, which uses it to synthesize hormones, primarily thyroxine (T4) and triiodothyronine (T3). These hormones are vital for regulating the body's metabolism, controlling energy usage, maintaining heart rate, and promoting growth and development. An iodine deficiency can lead to a range of health issues known as iodine deficiency disorders (IDD), including hypothyroidism and an enlarged thyroid gland, or goiter. In severe cases, especially during pregnancy and infancy, it can cause irreversible brain damage and intellectual disabilities. Conversely, excessive iodine intake can also disrupt thyroid function.

The Role of Geography in Iodine Content

The amount of iodine in food is heavily influenced by the soil and water where it was sourced. Soil in coastal regions generally contains higher levels of iodine than inland, mountainous areas. This geological factor explains why certain foods, particularly seafood, are naturally rich in this mineral, while land-grown crops and products from livestock in iodine-poor regions may have lower concentrations. This variation highlights the importance of fortified foods and supplements in ensuring consistent iodine intake for everyone, regardless of where they live.

Excellent Marine Sources of Iodine

Marine foods are arguably the best natural source of dietary iodine, as they absorb and concentrate the mineral from seawater. Seaweed is a powerhouse in this category, though its iodine content can vary significantly based on species and location.

Seaweed: Different varieties offer different amounts, with brown seaweed like kelp typically containing the highest levels. Nori (used in sushi) and wakame (popular in miso soup) are also excellent choices. However, kelp can contain very high amounts, so moderation is key.
Cod: This low-fat, saltwater fish is a fantastic source. A typical 3-ounce serving of baked cod can provide a significant portion of the daily recommended intake.
Shrimp and Oysters: Shellfish like shrimp and oysters concentrate iodine from their marine environment. Both are reliable sources, with cooked oysters providing a substantial amount per serving.
Canned Tuna: Depending on whether it's canned in oil or water, tuna provides a decent amount of iodine, making it a convenient option.

Dairy Products and Eggs

For many Western diets, dairy and eggs are significant contributors to iodine intake. The iodine content in dairy is influenced by the mineral supplements given to dairy cows and the iodine-based disinfectants used during milk processing.

Milk: A single cup of milk can provide a substantial amount of an adult's daily iodine needs.
Yogurt: Plain Greek yogurt is a concentrated source of iodine, offering more than half of the daily value in a standard ¾ cup serving.
Cheese: The iodine content in cheese varies by type, but many cheeses contribute to your overall intake.
Eggs: A large hard-boiled egg contains a notable amount of iodine, primarily in the yolk.

Fortified Foods and Other Sources

To combat iodine deficiency on a population-wide scale, many countries have implemented salt iodization programs, making iodized table salt a primary source for many.

Iodized Salt: A quarter teaspoon of iodized table salt can provide over half of an adult's daily needs. It is important to note that many processed and canned foods, which can be high in sodium, are often made with non-iodized salt, so checking labels is crucial.
Fortified Breads and Cereals: Some bread and cereal products use an iodate dough conditioner, which can significantly boost their iodine content.

Dietary Considerations for Vegans and Vegetarians

Vegans and vegetarians, who typically do not consume dairy, eggs, or seafood, can be at a higher risk of iodine deficiency. For these groups, ensuring adequate intake requires careful planning.

Seaweed: Certain types of seaweed, like nori, can be included in a balanced plant-based diet. However, due to the high variability and potential for excess intake from kelp, fortified sources are often recommended for consistency.
Plant-Based Fortified Milks: Some plant-based milk alternatives, such as soy or oat milk, are fortified with iodine. Always check the nutrition label, as not all brands contain this fortification.
Iodized Salt: This is a key source for all diets, including plant-based ones.
Other Plant-Based Sources: Certain vegetables and fruits, such as lima beans, potatoes, and prunes, can contain some iodine, though the amount depends on the soil's mineral content and is not reliable enough to be the sole source.

Iodine Content Comparison Table


Food Source	Serving Size	Approximate Iodine Content (mcg)	Percent Daily Value (DV)*
Seaweed (Nori)	2 tbsp dried flakes (5g)	116	77%
Cod (baked)	3 ounces	146	97%
Greek Yogurt	¾ cup	87	58%
Nonfat Milk	1 cup	84	56%
Iodized Salt	¼ tsp	78	52%
Cooked Oysters	3 ounces	93	62%
Hard-Boiled Egg	1 large	31	21%
Prunes (dried)	5 prunes	13	9%
Shrimp	3 ounces	13	9%

*Note: Based on an adult RDA of 150 mcg. Content can vary by product and source.

Conclusion

Maintaining an adequate dietary intake of iodine is essential for proper thyroid function and overall health. While marine foods like seaweed and cod are naturally high in this mineral, dairy products, eggs, and fortified foods like iodized salt also play a crucial role. For those following a vegan or vegetarian diet, careful attention to fortified products and moderate seaweed consumption is important to avoid deficiency. While most iodine is absorbed efficiently from food, the variability of natural sources makes fortified foods a reliable way to meet daily requirements. Always consider your dietary pattern and geographic location when evaluating your iodine sources and consult a healthcare provider with any specific concerns.

Important Information on Iodine

For more in-depth information and dietary guidance on iodine, consult the Health Professional Fact Sheet from the National Institutes of Health.

Note: The information provided here is for general knowledge and is not a substitute for professional medical advice. Always consult a healthcare provider for personalized recommendations, especially concerning supplements or thyroid health issues.

Frequently Asked Questions

For vegans, the most reliable sources are fortified foods like some plant-based milks and cereals, and iodized table salt. Some seaweed, like nori, is a good source, but portions must be managed carefully due to high variability.

No, natural sea salt contains minimal amounts of iodine unless it has been specifically fortified. The majority of iodine in people's diets comes from iodized salt.

The Recommended Dietary Allowance (RDA) for most adults is 150 micrograms (mcg) per day. Pregnant women need 220 mcg, and breastfeeding women need 290 mcg daily.

Some iodine can be lost during cooking, especially with high heat or prolonged cooking times. For example, some studies suggest a loss of 20-40% of iodine during cooking.

Yes, excessive iodine intake, often from high doses of supplements or frequent consumption of high-iodine seaweed like kelp, can lead to thyroid gland inflammation, hyperthyroidism, and other issues.

Iodine is critical during pregnancy for proper fetal brain and bone development. Maternal deficiency can lead to severe developmental delays and complications, including cretinism.

Dairy products contain iodine from the mineral supplements in cow feed and from iodine-containing disinfectants used to clean milking equipment. These methods ensure a consistent supply regardless of the soil quality.

It is unlikely to get sufficient iodine solely from fruits and vegetables, as the mineral content depends heavily on soil levels. In many areas, soil is iodine-poor, making this an unreliable source.

One of the most visible early signs of iodine deficiency is a goiter, or enlarged thyroid gland. Other symptoms include fatigue, weight gain, and increased sensitivity to cold.