Iodine: Finding the Right Balance for Thyroid Health

In the past Iodine deficiency was a serious problem, large numbers of people developed Goiter, a visible swelling of the neck caused by an enlarged thyroid gland, primarily because their diets lacked sufficient iodine, a trace mineral essential for thyroid hormone production. This was especially common in inland and mountainous regions where soils were naturally iodine-poor and access to seafood was limited. In the early 1900s, parts of the United States across the Great Lakes and Midwest, later known as the “Goiter Belt,” reported rates of thyroid enlargement in schoolchildren as high as 30 to 40 percent, while in Switzerland throughout the 19th and early 20th centuries, entire Alpine communities were affected, with severe deficiency sometimes leading to developmental disorders. Similar patterns were observed in Tasmania and New Zealand during the early to mid 20th century, where surveys of school populations revealed widespread iodine deficiency linked to local food systems. In response to this clear and preventable public health issue, iodisation of Table salt began in the 1920s, first in Switzerland in 1922 and in the United States in 1924, before being adopted more broadly in countries like New Zealand by 1939 and Australia through fortification programs in the following decades. By adding small, consistent amounts of iodine to a universally consumed staple, these interventions led to a rapid and sustained decline in goiter rates, making iodised salt one of the most effective and far-reaching nutritional public health measures ever implemented. However, despite this progress, iodine deficiency has not disappeared. It is still estimated to affect up to 30% of the global population.

If you regularly consume iodized salt, you are very likely getting enough iodine. But many modern dietary patterns are low salt and a growing number of people now use non-iodized salts such as Himalayan or Celtic sea salt, which contain only trace amounts of naturally occurring iodine, if any at all.

Others follow low-sodium or “SOS-free” diets, which eliminate added salt, oil, and sugar. While this approach may have benefits in certain contexts, removing iodized salt without replacing iodine from other sources can significantly reduce intake over time.

At the same time, iodine is not a nutrient where more is better. Both too little and too much can disrupt thyroid function. So how much iodine do you actually need? Where should you get it from? And how do you avoid both deficiency and excess?

What Is Iodine?

Iodine is an essential micronutrient, meaning your body needs it but cannot produce it on its own. You must obtain it from food or supplementation.

Its primary role is in the thyroid gland, a small butterfly-shaped organ at the front of the neck. The thyroid uses iodine to produce the hormones thyroxine (T4) and triiodothyronine (T3).

These hormones regulate your metabolic activity, which includes:

• How efficiently your body converts food into energy

• Your body temperature

• Heart rate

• Energy levels

• Brain and nervous system function

• Growth and development, particularly during pregnancy and infancy

Iodine levels are a limiting factor, which means that without sufficient iodine, your thyroid simply cannot produce enough of these hormones. When levels are too low, the system slows down. This often presents as:

• fatigue

• weight gain

• cold sensitivity

• mood disorder and reduced mental clarity

When iodine intake is excessive, the thyroid can become overstimulated or dysregulated, which may result in symptoms such as anxiety, restlessness, poor sleep, heat intolerance, and a racing heart.

The key is balance. Not too little, not too much.

How Much Iodine Do You Need?

Iodine is considered a trace mineral because the body requires only small amounts. The Recommended Daily Allowance (RDA) represents the minimum intake needed to maintain normal thyroid function.

Birth to 6 months: 110 mcg per day,

7 to 12 months: 130 mcg per day,

1 to 8 years: 90 mcg per day,

9 to 13 years: 120 mcg per day,

14 years and over: 150 mcg per day,

during pregnancy 220 mcg per day,

during lactation 290 mcg per day,

For most adults, a daily intake of around 150 micrograms is sufficient.

In practical terms, a useful target range is:

Around 100–200 mcg per day for general health, avoiding consistent intake below 80 mcg and avoiding regular intake above 300–500 mcg unless medically supervised. The tolerable upper limit for adults is 1,100 mcg per day, but this is a safety ceiling, not a goal.

Iodine Deficiency

Not getting enough iodine can lead to iodine deficiency disorders (IDDs), the most visible of which is Goiter, an enlargement of the thyroid gland.

Iodine is essential for the production of thyroid hormones, specifically thyroxine (T4) and triiodothyronine (T3). These hormones regulate metabolic rate, energy production, body temperature, and play a critical role in growth and neurological function.

When iodine intake is insufficient, the thyroid cannot produce adequate levels of T3 and T4. The body detects this drop through a feedback system involving the brain. The hypothalamus releases thyrotropin-releasing hormone (TRH), which signals the pituitary gland to release thyroid-stimulating hormone (TSH).

TSH travels through the bloodstream to the thyroid gland and acts as a direct signal to increase the production of T3 and T4. However, without enough iodine available, the thyroid cannot meet this demand. Instead, the gland responds by increasing in size, attempting to trap more iodine from circulation and boost hormone output. Over time, this constant stimulation causes the thyroid tissue to grow, leading to the development of goiter. This can lead to symptoms such as:

• Swelling in the neck

• Difficulty swallowing

• Coughing or breathing discomfort

Even without goiter, iodine deficiency can result in hypothyroidism, where the thyroid becomes underactive.

Symptoms commonly include:

• Fatigue

• Weight gain

• Cold intolerance

• Depression

• Infertility

Iodine Excess

While deficiency is a concern, excessive iodine intake can also disrupt thyroid function. Interestingly, the symptoms of excess iodine can overlap with deficiency, including goiter and hypothyroidism. In other cases, excess iodine can trigger hyperthyroidism, where the thyroid becomes overactive.

Symptoms may include:

• Anxiety and nervousness

• Mood swings

• Insomnia

• Heat sensitivity

• Muscle weakness

• Increased thirst and urination

Excess intake can also contribute to thyroid inflammation (thyroiditis), and in rare cases, increase the risk of thyroid disorders. Most cases of excess iodine come from supplements or very high intake of iodine-rich seaweeds, rather than whole foods in typical amounts.

Considerations for Thyroid Disease

If you have an autoimmune thyroid condition such as Hashimoto’s thyroiditis or Graves’ disease, iodine intake needs to be approached carefully.

In these conditions, the thyroid can be more sensitive to iodine fluctuations. High intake may worsen inflammation or disrupt thyroid regulation.

A steady, moderate intake from food sources is generally more appropriate than high-dose supplementation. Ensuring adequate selenium intake can also support thyroid function and help balance iodine metabolism.

Iodine Sources from Food

When it comes to iodine, the most important thing to understand is where it naturally comes from. Iodine is concentrated in the ocean. That means the richest and most reliable dietary sources are foods that either come directly from the sea or are influenced by it. From there, smaller amounts make their way into animal products and, to a far lesser extent, into plant foods depending on soil quality. So rather than thinking in terms of isolated foods, it’s more useful to think in categories:

• Marine foods (the most concentrated and reliable)

• Animal products (moderate and consistent)

• Plant foods (variable and often low)

The goal is to draw from one or more of these categories in a way that keeps your daily intake sitting comfortably around that 100–200 microgram range.

The Most Efficient Sources: Sea Vegetables

Sea vegetables are by far the most potent natural source of iodine. But they come with an important caveat: their iodine content varies dramatically.

Some types provide a clean, manageable amount. Others are so concentrated that even small amounts can overshoot your daily needs.

The most practical and balanced options when it comes to sea weed is

Nori, wakame, dulse, and arame.

In real terms, this is what that looks like:

A standard full sheet of nori, the kind used for sushi, typically contains somewhere in the range of 30 to 50 micrograms of iodine. That means two sheets in a day can cover a meaningful portion of your requirement without pushing you into excess.

Dulse is more concentrated. Around one teaspoon of dried dulse flakes, roughly one gram, can provide anywhere from 70 to 150 micrograms. In many cases, that alone is enough to meet your daily requirement.

Wakame sits in a similar range. A small teaspoon added to a soup or salad can easily contribute the majority of what you need for the day.

Then there are kelp varieties such as kombu. These are in a completely different category. A single gram can contain over 1,000 micrograms of iodine. That is several times the daily requirement in one small serving.

This is where people can unintentionally run into issues. Kelp is not inherently bad and can be an excellent way to ensure you get sufficient iodine in your diet, but it is something to use sparingly. As a general rule, if you’re using sea vegetables regularly, stick to the moderate sources and keep portions small and consistent.

Seafood: A More Stable Middle Ground

Seafood offers a far more predictable and balanced iodine intake.

Unlike seaweed, it is very difficult to overconsume iodine from fish in a normal diet, yet it still provides meaningful amounts.

For example, a standard 100 gram serving of cod can provide roughly 100 to 150 micrograms of iodine, which is enough to meet or come very close to your daily requirement in one meal. Prawns and shrimp tend to sit lower, usually around 35 to 50 micrograms per 100 grams, while tuna can vary between 20 and 50 micrograms depending on the type. What this means in practice is simple.

If you are eating seafood a few times per week, particularly white fish like cod, you are very unlikely to be deficient.

Eggs, Dairy, and Meat

Outside of marine foods, iodine intake becomes more moderate. Eggs are a useful contributor. One egg typically contains around 20 to 25 micrograms of iodine. Two or three eggs will give you somewhere between 40 and 75 micrograms. That’s not enough on its own, but it forms a solid base when combined with other sources.

Dairy can be a surprisingly effective source of iodine. A cup of milk or yogurt often provides between 50 and 100 micrograms, due to a combination of iodine in animal feed and the use of iodine-based sanitation practices during milking and processing.

Meat, on the other hand, is relatively low in iodine unless it has been specifically fortified through feed. A typical 100 gram serving of beef, lamb, or chicken may only provide between 5 and 15 micrograms. So while animal products can help, they rarely cover your needs on their own.

Plant Foods: Inconsistent but Worth Understanding

Some fruits and vegetables do contain iodine, including strawberries, cranberries, potatoes, and green beans. The challenge is that iodine content in plant foods is entirely dependent on the soil they are grown in.

In coastal regions, where iodine levels in the soil are higher, plant foods may contain more. In inland or mountainous regions, or areas with heavy rainfall where iodine is leached from the soil, levels can be extremely low. This is why plant foods are generally considered unreliable as a primary iodine source. They contribute, but they should not be relied upon exclusively.

A Simple Way to Cover Your Needs

Rather than tracking micrograms precisely, it’s far more practical to think in terms of one reliable daily source.

To meet the adult requirement of around 150 micrograms per day, aim to include at least one of the following in your day:

• One teaspoon of dulse flakes added to a meal

• One serving of white fish such as cod (around 100–150 grams)

• One cup of dairy (milk or yogurt) plus two to three eggs

• Regular use of iodised salt across your meals (roughly ½ teaspoon spread through the day)

  
  

Each of these options, on its own, is generally sufficient to bring your daily iodine intake into an adequate range. You don’t need to include all of them, and you don’t need to rotate perfectly every day. The key is consistency. As long as you regularly include at least one solid iodine source in your daily intake, you are very likely covering your needs.

Iodine Supplementation

Food should always be the foundation, but there are situations where supplementation becomes relevant. The most common are:

• Pregnancy and breastfeeding, where iodine requirements increase significantly.

• Plant-based diets, particularly those that avoid both seafood and iodized salt. Low-sodium diets, where iodized salt intake is minimal or absent.

• And cases of confirmed iodine deficiency.

Most standard multivitamins contain around 150 micrograms of iodine, usually in the form of potassium iodide. This aligns well with daily requirements and is generally considered a safe and effective baseline. Where things can become problematic is with standalone iodine supplements.

Many iodine supplement products contain 500 to 1,000 micrograms, or even higher doses. These are often marketed for thyroid support, but in many cases, they push intake well beyond what is necessary and into a range that can disrupt thyroid function over time. In fact, excessive iodine intake is one of the more common ways people unintentionally create thyroid issues while trying to “optimise” their health. For most people, if supplementation is needed, a dose in the range of 100 to 150 micrograms per day is more than sufficient. Anything beyond that should be approached with a clear reason and ideally with professional guidance.

Finding the Right Balance

Iodine is a small nutrient with big influence. It does not demand constant tracking, but it does require a basic level of awareness. If your diet regularly includes seafood, eggs, dairy, or small amounts of sea vegetables, your intake is likely sufficient without much effort. If those foods are largely absent, and you are using non-iodised salts such as sea salt, Himalayan salt, or other mineral salts in place of iodised salt, iodine becomes something that needs to be considered with more care.

The key is consistency. A steady, moderate intake over time is what supports normal thyroid function. Too little leaves the system under-supplied, while excessive intake can create its own complications. When it comes to iodine small gradual adjustments in diet or supplementation is the best strategy.

Most people do not need to micromanage iodine. They simply need to ensure that one reliable food source is present in their diet, day after day. With that in place, balance tends to take care of itself.

Medical Disclaimer

This article is intended for general educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Nutritional needs can vary significantly between individuals, particularly in the presence of underlying health conditions.

If you are considering iodine supplementation, or if you have a thyroid condition such as Hashimoto’s thyroiditis or Graves’ disease, it is important to seek guidance from a qualified healthcare practitioner. They can assess your individual needs and ensure that your iodine intake is appropriate and safe.

Always consult with a healthcare professional before making significant changes to your diet or supplement routine.

References

1. World Health Organization. Assessment of Iodine Deficiency Disorders and Monitoring Their Elimination: A Guide for Programme Managers. 3rd ed. Geneva: WHO; 2007.

2. National Health and Medical Research Council (NHMRC). Nutrient Reference Values for Australia and New Zealand. Canberra: NHMRC; 2006.

3. Zimmermann MB. Iodine deficiency. Endocrine Reviews. 2009;30(4):376–408.

4. Leung AM, Braverman LE. Consequences of excess iodine. Nature Reviews Endocrinology. 2014;10(3):136–142.

5. Institute of Medicine (US). Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academies Press; 2001.

6. Bath SC, Rayman MP. A review of the iodine status of UK pregnant women and its implications for the offspring. Environmental Geochemistry and Health. 2015;37(4):619–629.

7. Australian Institute of Health and Welfare (AIHW). Iodine Status in Australia. Canberra: AIHW; 2011.