Micronutrient of the Month: Iodine

Hi I’m Sammy, 

Your Good Farm in-house nutritionist. Here to bring you essential information on nutrition, diet and permaculture gardening - in a bite size, easy to understand, science-backed way.

Micronutrient of the Month: Iodine

Most of us know that iodine has something to do with the thyroid, and perhaps that it is added to salt. We need only a very small amount, around 150 micrograms a day for an adult, yet without it we cannot make thyroid hormones.

Thyroid hormones help regulate metabolism, energy, body temperature, growth and brain development. You could think of the thyroid as one of the body’s main control systems, helping to set the pace at which many parts of the body operate.

Like many micronutrients, too little iodine can cause problems, but so can too much. A low-functioning thyroid does not automatically mean you need more iodine. For some people, particularly those with autoimmune thyroid disease, taking large doses without understanding what is happening can make things worse.

Side note: This article gets a little meaty in parts because iodine and thyroid health are so closely connected. It is an area that has long interested me and one that I do not think always receives enough time or attention within our standard healthcare model. If the detail feels like too much, skip ahead to the fortification, food sources and essential takeaways. But if you have recently received a thyroid diagnosis, or feel that somet hing may be off, the deeper sections may be particularly useful.

Iodine and the thyroid

The thyroid is a butterfly-shaped gland at the front of the neck. It takes iodine from the bloodstream and uses it to make the hormones T4 and T3. T4 contains four iodine atoms and T3 contains three.

T4 is made in larger amounts and can be converted into the more active T3 throughout the body. Selenium is needed for this conversion and helps protect the thyroid during hormone production. Iron, zinc, vitamin A, protein and adequate food intake are also involved. As always, nutrients do not work in isolation.

When iodine intake is too low, the thyroid tries to capture more from the blood. TSH, the hormone that tells the thyroid to work, may rise. The gland can enlarge in its effort to keep up, causing a goitre. More significant deficiency can contribute to hypothyroidism.

Symptoms of an underactive thyroid can include fatigue, feeling cold, constipation, dry skin, hair changes, low mood, brain fog and menstrual changes. These are not proof of iodine deficiency and need to be considered alongside someone’s diet, history and test results.

The most serious effects of iodine deficiency occur during pregnancy and early childhood. Thyroid hormones are critical for a baby’s brain and nervous-system development, which is why iodine became a public-health issue. 

Why Is Iodine Added to Australian Bread?

Iodine deficiency began to re-emerge in Australia, particularly among children, women of child-bearing age and breastfeeding mothers. In response, the salt used in most bread was required to be iodised from 2009. Organic bread is exempt. Bread was chosen because it is widely eaten, and fortification has substantially reduced the number of Australians with inadequate iodine intake.

Fortification

Fortification has been effective in reducing iodine deficiency, but I still see it as a public-health safety net rather than the ideal foundation of our nutrition.

Added nutrients do not always come in the same form or arrive in the same nutritional context as they do in whole foods. Folic acid, for example, is not identical to the folate naturally found in food and must be processed differently by the body. The absorption of fortified iron also varies depending on the form used and the food to which it is added. This is one limitation of talking about fortification as though adding a nutrient back into a food completely recreates what occurs naturally.

Iodine is slightly different. The iodide or iodate added to salt can be used by the body to make thyroid hormones, so the fortified form itself is not necessarily inferior. The bigger question is the food carrying it. Most commercial breads are highly processed, and gluten, particularly its gliadin component, may increase intestinal permeability and contribute to immune dysregulation in susceptible people. This is especially relevant for people with coeliac disease, gluten sensitivity or autoimmune conditions, although it does not mean gluten causes autoimmunity in everyone. Either way, relying on a processed food to provide an essential nutrient is not ideal when iodine can be obtained naturally through nutrient-dense whole foods. Fish, oysters, eggs and dairy provide iodine alongside protein, selenium, zinc, omega-3 fats and other nutrients involved in thyroid and whole-body health. 

Fortification and supplementation have a role, particularly when deficiency is widespread or access to nutritious food is shaped by income and location. But they should fill gaps, not replace the nutrients and wider benefits found in whole foods, or move us further away from thinking about how nourishing our diet really is. 

Finding iodine naturally in food

Fish, oysters and other seafood are among our best natural sources. Canned salmon is affordable and easy to keep in the cupboard. Eggs and dairy also contribute iodine, although amounts vary. 

Seaweed is a great source of iodine, but the amount differs enormously between species and products. Nori is generally much lower than kelp or kombu. Kelp can contain many times the daily requirement in a small serve, so regularly eating large amounts or taking kelp capsules is not necessarily a safe or reliable approach.

Iodine in plants depends on the soil. Australian soils are generally low in it, so vegetables are not usually dependable sources. 

Thyroid Conditions

Hashimoto’s is an autoimmune condition in which the immune system mistakenly targets the thyroid, gradually reducing its ability to produce hormones. Graves’ disease is also autoimmune, but the antibodies stimulate the thyroid and can cause it to become overactive. Nodules, medications, pregnancy, illness, genetics, environmental toxins and other nutrient deficiencies can also affect thyroid function.

When someone with Hashimoto’s is prescribed thyroid hormone, the medication replaces what the thyroid can no longer produce adequately. This can be essential and, for many people, lifelong. It does not, however, directly address the autoimmune process that damaged the thyroid in the first place.

A functional approach looks at both parts of the picture. It replaces missing thyroid hormone where needed while also considering immune regulation, inflammation, nutrient status, gut and coeliac disease, stress, environmental exposures and other factors that may be relevant to that individual. Not every person will have one identifiable or reversible “root cause”, but that does not mean the wider picture should be ignored.

If someone is genuinely iodine deficient, restoring an appropriate intake is important. Large or sudden doses, however, can trigger or worsen thyroid dysfunction in susceptible people, particularly some people with Hashimoto’s, Graves’ disease or thyroid nodules.

The thyroid also uses selenium-containing enzymes to convert hormones and manage oxidative stress. Low selenium may leave it more vulnerable to a high iodine load, although this does not mean taking large amounts of both. Selenium supplementation has not been shown to help everyone with Hashimoto’s, and either nutrient can be harmful in excess.

I would be cautious with high-dose iodine drops, Lugol’s solution and kelp supplements without appropriate testing and guidance by an integrative professional.

Hashimoto’s also appears to be becoming more common, although it is difficult to know how much of this reflects a true rise and how much comes from greater awareness and more frequent antibody testing. 

There is unlikely to be one explanation. Hashimoto’s develops when genetic susceptibility meets one or more environmental influences. I remember epigenetics being explained at university like this: our genes load the gun, but our environment may pull the trigger. It is a simplified analogy, but a helpful one. Changes in iodine intake may be part of the picture, particularly when intake rises rapidly or becomes excessive. Pregnancy and the postpartum period can also alter immune activity, while certain infections, medications, radiation exposure and other autoimmune conditions may increase susceptibility.

Researchers are also investigating the possible roles of selenium and vitamin D status, environmental chemicals, chronic stress and the gut microbiome. What seems increasingly clear is that Hashimoto’s rarely has one simple root cause. It is more likely to develop through a combination of genetics, immune dysregulation, nutrient status, hormonal changes and environmental exposures.

Looking Beyond TSH

If you visit your GP with possible thyroid symptoms, testing will usually begin with TSH and sometimes free T4. These are starting points, but they do not tell the whole story. Thyroid antibodies, for example, can be present before TSH moves outside the laboratory range.

A more comprehensive panel may include TSH, free T4, free T3, thyroid peroxidase antibodies and thyroglobulin antibodies. Functional practitioners tend to look at how these results sit together, alongside symptoms, health history and changes over time.

They may also use a narrower TSH range, often around 0.5 to 2.0 or 2.5 mIU/L, compared with laboratory ranges extending to around 4.0 or 4.5. These are not universally accepted diagnostic cut-offs. A result outside a functional range does not prove thyroid disease, but it may be a reason to look more closely, particularly when symptoms or antibodies are also present.

Age, pregnancy, illness, medication and even biotin supplements can affect thyroid results, so no number should be read in isolation.

A thyroid panel measures thyroid function, not iodine status. Urinary iodine is useful for assessing populations, but a single result can change with recent food and fluid intake. Often the best place to begin is with the diet. Do you regularly eat seafood, seaweed, eggs or diary? Do you exclude those foods but eat fortified bread? Is your salt iodised? Are you pregnant, breastfeeding or following a restrictive diet?

Iodine and breast health

The thyroid is not the only part of the body that uses iodine. Breast tissue also draws iodine into its cells, and during breastfeeding it concentrates iodine into breast milk to support the baby’s thyroid and brain development.

Researchers are still exploring what iodine may mean for breast health, including breast pain and fibrocystic changes, but the evidence is not strong enough to say that iodine prevents breast cancer or that high-dose supplements are beneficial.

For me, it is another reason to make sure iodine-rich foods have a place in the diet. 

The Takeaways

Seaweed is one of the richest sources of iodine, but its iodine content varies enormously. Kelp and kombu can provide far too much in a small amount, so more is not necessarily better.

Iodine is also found in fish, oysters, eggs and dairy.

Be cautious with high-dose iodine drops, kelp products and iodine supplements, particularly if you have Hashimoto’s, Graves’ disease or thyroid nodules. Seek individual advice before using them.

Fortification can help prevent widespread deficiency, but adding an isolated nutrient does not recreate the broader nutritional package found in whole foods, particularly when the food being fortified is itself highly processed.

Thyroid results can sit within the laboratory range while symptoms persist or antibodies are present. This does not prove thyroid dysfunction, but it may warrant a closer look.

Functional practitioners often use narrower ranges and consider symptoms, health history and trends alongside the numbers. These ranges are investigative guides, not universally accepted diagnostic cut-offs.

Selenium also needs to be considered alongside iodine, as the two work closely together in thyroid health. Stay tuned for a future Micronutrient of the Month article on selenium.

Trust your instincts. If something does not feel right, keep asking questions. This may mean requesting further investigation, booking a longer appointment or finding a qualified practitioner who takes an integrative or functional approach.

At The Good Farm Shop, we believe nutrient density begins with how food is grown and animals are raised. For iodine specifically, look for meals containing fish, eggs or dairy, depending on what you eat and tolerate. These foods also provide protein, selenium, zinc and other nutrients that work alongside iodine.

Our Yellow Fish Curry and Anouk’s Tuna Mornay are two great options, but Fish Pie is my favourite way to put this month’s micronutrient into practice.

Stay tuned for next week, when we begin our Milk Series with Part One: Dairy Milk, followed by Part Two: Non-Dairy Milks.

If you enjoy these articles and would like to see a particular topic explored in The Nutrition Edit, please leave a comment below or send us an email.

References

Food Standards Australia New Zealand. Iodine Fortification.

National Health and Medical Research Council. Iodine Supplementation for Pregnant and Breastfeeding Women.

National Institutes of Health, Office of Dietary Supplements. Iodine: Fact Sheet for Health Professionals.

Smyth, P.P.A. “Iodine, Seaweed and the Thyroid.” European Thyroid Journal, 2021.

Klubo-Gwiezdzinska, J. and Wartofsky, L. “Hashimoto Thyroiditis: An Evidence-Based Guide to Etiology, Diagnosis and Treatment.” Polish Archives of Internal Medicine, 2022.

Kalarani, I.B. and Veerabathiran, R. “Impact of Iodine Intake on the Pathogenesis of Autoimmune Thyroid Disease in Children and Adults.” Annals of Pediatric Endocrinology & Metabolism, 2022.