Do onions have iodine in them? An Exploration of This Common Vegetable's Mineral Content

January 13, 2026 •

3 min read

Soil composition heavily influences the mineral content of plants, which is why the amount of iodine in vegetables like onions is highly variable. While onions do contain trace amounts of iodine, they are not considered a significant or reliable dietary source of this essential nutrient. For most people, iodine intake comes from more dependable sources.

Quick Summary

Onions contain trace amounts of iodine, but the levels are very low and inconsistent, depending largely on the soil in which they were grown. They are not a primary source of this mineral, and more reliable intake comes from other foods, such as seafood, dairy products, and iodized salt.

Key Points

Trace Amount Present: Onions do contain iodine, but only in very small, trace amounts that are not considered a significant dietary source.
Content Varies: The amount of iodine in an onion is highly inconsistent and depends on factors like the iodine content of the soil and irrigation practices where it was grown.
Not a Primary Source: You cannot rely on onions to meet your daily iodine requirements; better sources are needed for adequate intake.
Richer Sources Exist: Much more reliable dietary sources of iodine include seafood, dairy products, eggs, and most commonly, iodized table salt.
Important for Thyroid Health: Iodine is essential for the production of thyroid hormones, and deficiency can lead to significant health problems, including hypothyroidism and goiter.
Geographic Influence: Because most iodine is in the ocean, plants grown in coastal areas might naturally contain more than those grown inland, though levels are still generally low.

The Truth About Onions and Iodine Content

Onions are a staple in kitchens around the world, prized for their flavor and nutritional benefits. They are rich in vitamins, fiber, and compounds like quercetin. However, when it comes to the essential trace mineral iodine, onions are not a powerhouse food. A 2025 analysis of iodine-rich foods listed onions with a negligible iodine content, providing only about 3 micrograms (mcg) per 100 grams. In contrast, seaweed contains dramatically higher levels, with some types offering thousands of micrograms per 100 grams. This is because iodine is naturally abundant in oceans and coastal soils, while inland soils are often depleted of this mineral due to factors like glaciation, flooding, and erosion.

Factors Influencing Iodine in Plant-Based Foods

Beyond the low baseline amount, the iodine content in any given onion can be highly inconsistent. The primary reason for this variability lies in the environment where the plant was cultivated. Key factors include:

Soil Composition: The iodine level in the soil directly determines how much of the mineral can be absorbed by the onion plant. Crops grown in iodine-deficient soils will naturally have lower concentrations. Many parts of the world, especially inland and mountainous regions, have naturally iodine-poor soil.
Fertilizer and Irrigation: The type of fertilizers and water used can also affect the mineral profile of the soil and, by extension, the plants growing in it.
Geographic Location: Given the ocean's role as a major iodine source, vegetables grown near coastal regions may have higher iodine content than those grown inland.
Cultivar and Variety: Different varieties of onions may also vary slightly in their ability to absorb and store minerals, though soil remains the most significant factor.

Comparison of Iodine in Common Foods

To put the iodine content of onions into perspective, it's helpful to compare it with other dietary sources. The following table illustrates the vast difference in iodine concentration across various foods, highlighting why onions are not a recommended source for meeting daily iodine needs.


Food Source	Approximate Iodine Content (per 100g)	Reliability as Iodine Source
Seaweed (Kelp)	1,736 mcg	High (but can vary greatly)
Cod (baked)	146 mcg (per 3 oz)	High
Greek Yogurt (plain, nonfat)	87 mcg (per 3/4 cup)	High
Iodized Table Salt	45 mcg (per 1g)	High (when added)
Egg (hard boiled)	31 mcg	Moderate
Potatoes	7 mcg	Low to Moderate
Onions (raw)	~3 mcg	Very Low
Non-Iodized Sea Salt	0 mcg	None

Strategies for Meeting Your Iodine Needs

Since relying on onions for iodine is not practical, it's important to know the best and most consistent dietary sources. Here are some strategies for ensuring adequate iodine intake:

Use Iodized Salt: The most common and effective way to prevent iodine deficiency is through the use of iodized salt. This practice has been implemented in many countries for decades and remains a simple solution.
Eat Seafood: Marine fish and other types of seafood are excellent natural sources of iodine. Incorporating a variety of seafood, like cod, shrimp, and tuna, into your diet is highly beneficial.
Incorporate Dairy Products: Milk, yogurt, and cheese are all good sources of iodine, particularly in the United States, where dairy is a significant contributor to intake.
Consider Eggs: A single hard-boiled egg can provide a decent amount of iodine, making it a good dietary option.
Include Seaweed: For those following a vegan or vegetarian diet, seaweed is a very potent source of iodine, though it's important to monitor intake due to the high concentration.

For more detailed information on reliable iodine sources and recommended intake levels, you can consult the NIH Office of Dietary Supplements website.

Conclusion: Onions as a Flavor, Not an Iodine Source

While onions offer numerous health benefits, their contribution to your daily iodine intake is minimal and highly unreliable. They should be celebrated for their rich flavor and antioxidant properties, but not as a primary source of this crucial mineral. For consistent and adequate iodine levels, it is best to rely on established dietary sources like seafood, dairy, and, most simply, iodized salt. A well-rounded diet that includes these reliable sources will better support overall thyroid health and prevent deficiency.

List of Reliable Iodine Sources

Seafood: Fish, shellfish, and seaweed contain some of the highest concentrations of iodine.
Dairy Products: Milk, cheese, and yogurt are important dietary contributors of iodine.
Eggs: A good, easily accessible source of iodine for many diets.
Iodized Salt: The most widely used and effective method for preventing iodine deficiency.
Fortified Breads and Cereals: Some grain products are fortified with iodine, although this varies.

Frequently Asked Questions

No, onions are not considered high in iodine. While they do contain trace amounts, the quantity is very low and unreliable as a significant dietary source.

Most fruits and vegetables are poor sources of iodine. The best plant-based source is seaweed, such as kelp and nori, which contain very high levels.

The primary reason for the variation in iodine content among vegetables is the iodine level in the soil where they are grown. Soil quality and geographical location are the most influential factors.

It can be challenging to get enough iodine from a strictly plant-based diet without careful planning, as the richest sources are seafood and dairy. Vegans should consider including seaweed or using iodized salt to ensure adequate intake.

Yes, iodized salt is a very reliable and common source of dietary iodine. The process of adding iodine to salt is the most widespread strategy for preventing iodine deficiency.

The best food sources of iodine include seafood (fish, shrimp, seaweed), dairy products (milk, yogurt, cheese), eggs, and iodized table salt.

Iodine deficiency can lead to health problems like an enlarged thyroid gland (goiter) and an underactive thyroid (hypothyroidism), which can cause fatigue, weight gain, and sensitivity to cold.