Does Fish Oil Contain Iodine? The Surprising Answer for Your Nutrition Diet

October 8, 2025 •

4 min read

Over 70% of the body's iodine is stored in the thyroid gland, which requires it for the production of critical metabolic hormones. So, does fish oil contain iodine? Contrary to what some might assume, the highly purified fish oil found in most supplements contains only trace or undetectable levels of iodine.

Quick Summary

Highly purified fish oil supplements contain negligible iodine, as the mineral is not soluble in oil and is effectively removed during processing. These supplements provide omega-3s, while dietary iodine for thyroid function must be sourced elsewhere.

Key Points

Iodine is Removed During Processing: Reputable fish oil manufacturers use molecular distillation to remove contaminants, including the iodine that is naturally present in fish.
Purified Fish Oil Has Negligible Iodine: Test results from high-quality fish oil supplements show iodine content is trace or undetectable, making them an unreliable source for this mineral.
Iodine and Omega-3s Serve Different Purposes: Iodine is crucial for thyroid hormone production, while fish oil primarily provides anti-inflammatory omega-3 fatty acids for heart and brain health.
Rely on Whole Foods for Iodine: To meet your daily iodine needs, incorporate dietary sources like seaweed, dairy products, eggs, and iodized salt into your nutrition diet.
Fish Oil Can Indirectly Support Thyroid Health: The anti-inflammatory effects of omega-3s may be beneficial for individuals with autoimmune thyroid conditions like Hashimoto's, but it is not a direct treatment.
Check Your Supplement Source and Type: Some marine-derived supplements, like seaweed or kelp, are specifically for iodine, while cod liver oil offers Vitamin A, D, and some omega-3s along with variable, though usually low, iodine content.

The Surprising Reality: Low to Non-Existent Iodine Content

When considering your nutrition diet, it's a common misconception that fish oil supplements are a reliable source of iodine simply because the oil comes from fish. In reality, the sophisticated manufacturing process used to create high-quality fish oil intentionally removes nearly all of the naturally occurring iodine. This is a crucial distinction to understand, especially for individuals monitoring their iodine intake for thyroid health.

The Purification Process That Removes Iodine

Reputable fish oil manufacturers employ advanced purification methods to ensure their products are safe, pure, and free from contaminants. One of the most effective techniques is molecular distillation. During this process:

The fish oil is heated in a vacuum to separate its components based on their boiling points.
Contaminants like heavy metals (e.g., mercury) and persistent organic pollutants are removed.
Importantly, inorganic salts, including the iodide naturally present in the fish, are not soluble in the oil and are filtered out.

The result is a highly concentrated, ultra-pure omega-3 oil with an iodine content so low it is often considered undetectable. Test results from manufacturers typically show iodine levels well below 2.0 mcg/g, which is negligible compared to the recommended daily allowance of 150 mcg for most adults.

Fish Oil vs. Iodine: Different Roles in Your Body

It's essential to recognize that fish oil and iodine serve fundamentally different, yet important, roles in the body. They are not interchangeable nutrients.

The Importance of Iodine for Thyroid Function

Iodine is a critical mineral that the body cannot produce on its own. Its primary function is to enable the thyroid gland to produce the hormones thyroxine (T4) and triiodothyronine (T3). These hormones are responsible for regulating metabolism, energy levels, and overall growth and development. Iodine deficiency is a significant global health problem that can lead to thyroid enlargement (goiter) and, in severe cases, impaired neurodevelopment.

Common Dietary Sources of Iodine

Seafood: White fish like cod and haddock contain more iodine than oily fish. Shellfish such as shrimp and oysters are also excellent sources.
Dairy Products: Milk, yogurt, and cheese are good sources, though iodine levels can vary.
Eggs: The yolk is a good source of iodine.
Iodized Salt: The most widespread source, especially in countries with salt-iodization programs.
Seaweed: Kelp, nori, and wakame are exceptionally rich in iodine, but amounts can vary greatly.

The Power of Omega-3s in Fish Oil

Fish oil's primary health benefit comes from its high concentration of omega-3 fatty acids, specifically eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These polyunsaturated fats are vital for:

Reducing Inflammation: Omega-3s have potent anti-inflammatory effects throughout the body.
Heart Health: They can lower triglycerides, reduce blood pressure, and improve overall cardiovascular function.
Brain Health: DHA is a key component of brain cell membranes and is crucial for cognitive function and development.
Immune System Modulation: Omega-3s can help regulate immune responses, which may benefit those with autoimmune conditions.

The Potential Link to Thyroid Health

While fish oil is not a direct source of iodine, its anti-inflammatory effects can still offer support for thyroid health, particularly in cases of autoimmune thyroid conditions like Hashimoto's thyroiditis. By helping to calm chronic inflammation, omega-3s may indirectly support better thyroid function and overall well-being. However, fish oil is not a treatment for thyroid disease and should not be used as a replacement for medical advice or prescribed medication.

Comparison Table: Fish Oil, Cod Liver Oil, and Seaweed Supplements

To further clarify the distinction in iodine content, here's a side-by-side comparison of three common marine-derived supplements.


Feature	Purified Fish Oil	Cod Liver Oil	Seaweed/Kelp Supplement
Primary Purpose	Omega-3 (EPA/DHA) source	Omega-3, Vitamin A & D source	High Iodine Source
Iodine Content	Trace or undetectable amounts	Variable, but generally low after processing	Very high and variable
Omega-3 Levels	High, often concentrated	Contains omega-3, but lower than concentrated fish oil	Typically very low or none
Other Nutrients	Primarily EPA & DHA	Rich in Vitamin A and Vitamin D	Other minerals and fiber
Best For	Boosting omega-3 intake with minimal iodine	Vitamin A & D deficiency plus omega-3s	Individuals with low iodine intake needs

Conclusion: Making Informed Supplement Choices

To summarize, the answer to "does fish oil contain iodine?" is a definitive no, not in any significant, beneficial amount. The purification methods used to create high-quality fish oil effectively strip out the naturally occurring iodine, leaving behind the concentrated omega-3 fatty acids. This distinction is vital for those managing their nutrition diet and particularly for those with thyroid conditions who need to carefully control their iodine intake. For iodine, rely on established dietary sources like dairy, eggs, seafood, or iodized salt. For omega-3s and their powerful anti-inflammatory benefits, purified fish oil is an excellent choice. Always consult with a healthcare provider before beginning any new supplement regimen to ensure it aligns with your specific health needs.

For more detailed information on iodine's role in health, you can refer to the National Institutes of Health (NIH) Office of Dietary Supplements: Iodine - Health Professional Fact Sheet

Frequently Asked Questions

Fish contains iodine, but during the manufacturing process, the oil is extracted and then purified through processes like molecular distillation. Iodide, the form of iodine in fish, is not soluble in the oil and is removed along with other impurities.

No, you should not rely on purified fish oil supplements to meet your daily iodine requirement. These supplements contain only trace amounts of iodine or none at all, and their primary purpose is to provide omega-3 fatty acids.

Excellent dietary sources of iodine include seafood like cod and shrimp, dairy products such as milk and yogurt, eggs, and especially seaweed (kelp, nori). Iodized salt is also a major source.

Cod liver oil contains omega-3s, as well as Vitamins A and D. While it may contain some residual iodine, the amounts are highly variable and generally not sufficient to be considered a primary iodine source, unlike whole cod fish.

Yes, some marine supplements, particularly kelp and seaweed, can have very high and variable iodine levels. It is important to be aware of the iodine content to avoid excessive intake, which can negatively affect thyroid function.

The omega-3 fatty acids in fish oil have anti-inflammatory properties that may indirectly benefit thyroid health, especially in autoimmune conditions like Hashimoto's. However, it does not replace the iodine needed for hormone production.

Look for a high-quality fish oil supplement that has been molecularly distilled to remove contaminants and contains a high concentration of EPA and DHA. The label should specify the amounts of EPA and DHA per serving.