top of page


What you need to know about Iodine 

Iodine is an essential trace mineral specifically required by the thyroid gland to produce thyroid hormones in the regulation of normal metabolism. Iodine enriched thyroid hormones are crucial in the conversion of energy obtained from food into the energy required by the body to power all cellular activities, growth and development.

thyroid matters, thyroid disorders,iodine an essential micronutrient,thyroidmatters, thyroid disorders,iodine, iodine deficiency, iodine toxicity, thyroiditis, thyrotoxicosis, hypothyroidism, hyperthyroidism, hashimotos graves disease, nodules, goitre, autoimmune thyroid conditions, kelp supplements, underactive thyroid gland, overactive thyroid

There is little doubt that iodine is fundamental to human health. The question is, how much do we need for healthy thyroid function, and is supplementing with iodine necessary, especially for those with normal thyroid function or pre-existing thyroid conditions?  

Let's look at some key facts:

  • Iodine is an essential trace mineral that plays an important role in maintaining the health and function of your thyroid gland and your entire body.

  • The thyroid gland, located in the base of your neck, produces specific iodine-rich hormones that help regulate normal metabolism, energy production, cellular activities, and proper skeletal and central nervous system development in fetuses and infants.

  • Iodine is the main raw material that the thyroid gland uses to manufacture thyroid hormones - the two most significant hormones being thyroxine, T4 (containing 4 iodine atoms) and triiodothyronine, T3 (containing 3 iodine atoms). When the cells of the body require thyroid hormone, one iodine atom is removed from T4, and T4 is converted into active T3.

  • Not only is iodine the main building block in the production of thyroid hormones, but trace amounts are also essential for the health of the breasts, ovaries, testes and prostate. When iodine is sufficient, the development of fibroids, cysts and nodules in any gland is less likely to occur.

  • Iodine is known for its powerful antibacterial, antifungal and antiviral properties, supporting the immune system by neutralising infectious pathogens, detoxifying and reducing toxins, and binding to heavy metals for elimination.

  • Iodine is not naturally produced within the body, therefore a constant supply from foods sources is needed to meet the body's demands to maintain health.

  • Goitre (swollen and enlarged thyroid gland) is usually the most obvious sign of iodine deficiency.

Iodine Deficiency

  • Without sufficient iodine, the thyroid gland cannot produce adequate amounts of thyroid hormone, and if left untreated will result in Hypothyroidism (low thyroid function). Poor thyroid hormone levels cause all metabolic processes to slow down and can lead to symptoms like unrelenting fatigue, weakness, cold intolerance, poor memory and concentration, body aches and pains, weight gain, dry skin, hair loss, and swelling in the front of the neck (goitre).

  • People most at risk for iodine deficiency include those living in areas with low levels of iodine in the soil, or living in mountainous regions further from the ocean. In areas around the world with severely deficient soils and a lack of dietary iodine, the majority of the inhabitants suffer from hypothyroidism and goitres. This is particularly a problem for babies, children and pregnant women because thyroid hormone is needed for normal fetal growth and brain development. Mental retardation and cretinism can result if the deficiency is not corrected early enough during pregnancy and after birth. These regions are often referred to as ‘goitre belts’.

  • Thyroid specialists and the World Health Organization have developed national programs in many countries to eliminate iodine deficiency world wide. The simple introduction of iodised salt or iodised vegetable oil to the diet prevents the risk of iodine deficient-related thyroid disease. Iodine deficiency has been rectified in most Western countries but is still a problem in many developing nations. Iodine deficiency continues to be the most common cause of an underactive thyroid gland throughout the world, and is still considered the most common cause of preventable fetal brain damage.

  • You would think that living in a wealthy nation, rich in food sources, that iodine deficiency would be unheard of, but over recent years many countries have experienced a re-emergence due to depleted soils and a lack of monitoring of iodine nutrition. In developed nations like Australia, those at risk for iodine deficiency include, pregnant women, vegans on a strict diet that excludes animal food sources, those on a low salt diet to prevent hypertension and heart disease, those not consuming fortified foods like breads, pasta and dairy products, and who do not use sea salt or iodized salt in cooking. A mild to moderate deficiency in iodine can still be particularly dangerous for pregnant women and young children, increasing the possibility of reduced fertility, pregnancy complications, miscarriage, stillbirth, and childhood developmental delays and cognitive impairments. Even for healthy adults a mild deficiency of iodine can disrupt normal metabolic functions and affect heart rate, energy production, cognitive ability, body temperature, and weight.

  • In Australia, Gippsland, Canberra, Sydney and Tasmania are areas already known to have iodine deficient soils. However, In the early 2000s, iodine deficiency began emerging all over Australia after the dairy industry changed their cleaning products from iodine based disinfectants to chlorine based. The healthy levels of iodine residual usually found in all dairy products gradually disappeared and the Australian population was beginning to feel the effects of poorer thyroid function. Nation wide urinary iodine testing was initiated and the studies found that 50% of pregnant women and school children were mildly to moderately deficient in iodine. Endocrinologists and thyroid support groups raised the alarm, and health authorities approached the food industry so that breads and most flours were fortified with iodine to correct this health crisis.

When it comes to iodine, the more the better is not the case... It's all about finding a balanced intake, and everyone is different.

thyroid matters, thyroid disorders,iodine, hypothyroidism, iodine deficiency and excess, iodine toxicity, thyroid conditions, autoimmunity, hyperthyroidism, toxic goitre, thyroid cancer, thyrotoxicosis

Iodine Excess

  • Interestingly, one of the most common triggers of thyroid dysfunction in developed nations is iodine excess. Over zealous consumption of iodine supplements, and eating large quantities of seaweed and seafood can cause a toxic rise in iodine levels within thyroid tissue. This may lead to the development of thyroiditis, hypothyroidism, hyperthyroidism, 'hot' nodules, multinodular goitre, or thyroid papillary cancer. The type of condition that could arise will depend on a person's general thyroid function, predisposition to thyroid disease, nutritional status and their basic genetic makeup.

  • Autoimmunity: Iodine excess can also trigger autoimmune thyroid diseases such as Hashimoto's Thyroiditis and Graves' Disease, as toxic levels of iodine accumulate within thyroid cells and trigger an immune system response, especially in those with an inherited predisposition for thyroid disease. Iodine supplementation has been known to make autoimmune processes more aggressive and increase the destruction of thyroid tissue, or over stimulate the gland, further contributing to thyroid dysfunction.

  • Generally, high iodine intake is well-tolerated in most healthy people and does not cause any problems, however, for sensitive individuals, even a slight increase in dietary iodine, above the recommended daily allowance, can cause iodine-induced  hyperthyroidism. The abnormal increase in metabolism may lead to symptoms that include, heat intolerance, shortness of breath,  increased sweating, fast or irregular heartbeat, chest pains, hand tremors, irritability and weight loss.

  • Severe iodine poisoning is extremely rare, but it still does occur. Those particularly vulnerable are infants, young children and the elderly, and those with pre-existing thyroid disease. Iodine poisoning can present with stomach pain, nausea, vomiting, fever, painful thyroid gland, difficulty swallowing, and a burning sensation of the mouth, throat, and stomach.

  • Warning: For those diagnosed with Graves' Disease or toxic nodules, taking iodine is like pouring fuel on the fire, and will only make things worse. Iodine supplements and iodine rich foods should be avoided so as not to feed thyroid cells and encourage overactivity of the gland. Iodine is not recommended for treating hyperthyroidism, unless a block and replace therapy is given under specialist supervision. Aggressive thyrotoxicosis fuelled by iodine intake can lead to a life threatening event known as a 'Thyroid Storm'. This event requires immediate medical attention due to dangerously high levels of thyroid hormones in the bloodstream. Emergency hospitalisation and treatment is vital to reduce thyroid hormone levels as quickly as possible, to avoid brain damage, coma or even death.


When it comes to iodine, the more the better is not the case. The body only requires trace amounts to function optimally and maintain healthy thyroid function. It's all about finding a balanced intake, and everyone is different.

  • Before taking any supplements, iodine levels should be assessed and discussed with your doctor. It is important that your doctor is kept up to date with any changes in medications or nutritional supplementation, so that interactions and side effects can be monitored.

  • Urinary iodine measurements (24-hour) are a useful indicator of a persons iodine status. Urinary iodine concentrations directly reflect iodine intake as the body excretes more than 90% of dietary iodine in the urine. For adequate iodine nutrition the medium urinary iodine concentrations should be between 150-250 mcg and never less than 100-150mcg.  

  • RDA: The recommended daily allowance of 150mcg of iodine is all the thyroid gland needs for healthy function, and between 200 to 300mcg is recommended for pregnant and lactating women and those with a mild deficiency. Sufficient iodine can be obtained by consuming foods rich in iodine, however, supplementation is sometimes required where the diet is lacking or if a person has poor absorption of this mineral.

  • UL: In the general population, the tolerable upper intake level (UL) of iodine, considered safe and unlikely to cause adverse side affects, is around 1,000 mcg daily. This maximum dosage is considered relatively safe for most healthy individuals and those with iodine deficiencies, but sensitive individuals or those with underlying thyroid conditions, should not exceed 500mcg daily.

  • Medical studies suggest that consuming more than 1.1 milligrams per day of iodine may be particularly harmful for those with pre-existing thyroid disease, the elderly, fetuses and newborns. Acute and/or chronic iodine toxicity can cause subclinical or overt thyroid dysfunction in patients with specific risk factors.

  • Please note, most iodine supplements come in microgram quantities, i.e. mcg, and not milligrams (mg). Supplements providing 1 milligram of iodine = 1000 micrograms, and this generally far exceeds standard recommendations.

  • Kelp: please be aware... Kelp and kelp supplements are generally not recommended for thyroid patients or pregnant women, due to containing highly concentrated levels of iodine and possible contaminants. Many supplements have been found to have more than twice the amount of iodine than stated on the label. Kelp products can contain anywhere from 150 micrograms to 3,000 mcg per gram of product.

  • Poorly regulated kelp products vary from batch to batch and have the risk of contamination with various heavy metals and toxins, including arsenic. Before considering supplementing with kelp, it is worth doing your research to make sure the levels of iodine in a particular brand are well regulated, not too excessive, and proven to be free from pollutants. Please consult with a healthcare professional first, and do not self medicate. 

  • Selenium and Zinc: Doctors, naturopaths and integrative specialists may recommend zinc and selenium when prescribing iodine, as these aid in efficient thyroid hormone production, utilisation, and conversion of T4 into T3. However, serum levels of zinc and selenium should always be assessed before supplementation is given. Selenium, in particular, can be toxic at higher levels, so self-administration should be avoided.  

  • Selenium works in synergy with iodine. It is a powerful antioxidant that protects thyroid tissue from oxidative stress and can hinder the negative effects of excess iodine intake. Selenium also safeguards the thyroid gland from inflammatory autoimmune processes and has shown to be effective in lowering thyroid antibody levels. The richest source of selenium is found in Brazil nuts, and usually only 2-4 per day will provide the recommended daily intake.

  • Consuming excess iodine from certain foods, on occasions, is unlikely to cause problems in most people, as the body has mechanisms to balance and eliminate what is not needed in the short term. When it comes to regular high dose supplementation, a simple reduction in iodine intake can reverse any unwanted effects if they begin to appear, thus avoiding more serious complications.

  • However, generally speaking, it is not recommended to consume high levels of iodine on a daily basis without first consulting a healthcare practitioner. Long term intake above the RDA may adversely affect thyroid function causing goitre, inflammation of thyroid tissue, nodule growth, and abnormal thyroid hormone levels. Consistently high intake can lead to the development of more permanent conditions, such as, autoimmune thyroid disease, overt hypothyroid, hyperthyroidism and even thyroid papillary cancer.

  • Consuming safe amounts of iodine rich foods, and adhering to recommended daily allowances of iodine will minimise the risk of triggering a thyroid imbalance, and causing autoimmune flare ups. Moderation is key to avoiding any iodine toxicity. 

Sources of iodine


  • The richest sources of iodine are found in soil and the ocean, but the amount of this mineral can vary from place to place which will affect how much is contained within various food sources.

  • The highest levels of iodine are found naturally in sea salt, seaweed and sea vegetables (kelp, nori, kombu and wakame), and seafood (saltwater fish, shellfish, cod, tuna, oysters and shrimp).

  • Iodine is found in moderate amounts in eggs and animal protein foods, like beef, liver and chicken, and vegetables grown in soil with adequate iodine.

thyroid matters, thyroid disorders,iodine, iodine deficiency, kelp, seaweed, hypothyroidism, hashimotos, hyperthyroidism, graves disease, thyroid conditions, underactive, overactive, iodine toxicity, autoimmunity, thyroiditis


  • Food sources fortified with iodine include breads, cereals, and dairy (milk, yoghurt and cheese), in smaller concentrations.

  • Iodine can be obtained by using table salt labelled "iodized", but it is wise to find a form of salt that is rich in nutrients and doesn't contain toxic substances through its refining processes.

  • Kelp supplements are not recommended for pregnant or nursing women. The safest form of supplemental iodine, particularly for this group, comes in the form of potassium iodide. This guarantees purity and regulated dosage, and provides the most highly absorbed form of iodine. 

  • Seaweed is an excellent source of iodine and other nutrients, however, the amount of iodine content varies depending on the species, where it is grown, and how it is processed. Kombu kelp (a brown seaweed) offers the highest amount of iodine, but it generally far exceeds safe levels for human ingestion, unless greatly diluted or used sparingly.

  • Organic sea kelp (Icelandic) is probably one of the safest forms of kelp, known to be free from contaminants. 

  • Nori is a species of red seaweed that is commonly used in sushi rolls. Unlike brown seaweeds, nori has a much lower and healthier level of iodine content, ranging between 16–43 mcg per gram. Eating sushi on a regular basis is a great way of receiving a healthy dose of iodine without any risk of iodine toxicity.

  • For more severe iodine deficiencies a supplement of iodine in liquid form can be recommended or prescribed by a doctor, however, iodine levels must be tested before consuming more concentrated products.

  • Always consult with a doctor and be carefully monitored when taking any iodine supplement, especially if you have a thyroid condition, are pregnant or nursing infants.


  • In Australia, the population obtain most of their dietary iodine from iodized salt, bread and milk, and from eating seafood on a regular basis.

  • Concentrated iodine is an ingredient used in contrast agents which are given to patients before having an X-ray or CT scan. It helps in obtaining clear pictures of the body’s organs for diagnostic purposes. Contrast mediums could be a problem for those with pre-existing thyroid conditions, especially those diagnosed with hyperthyroidism or autoimmune thyroid disease.

  • Iodine supplements can interact with certain blood pressure medications and diuretics, causing a dangerous build-up of potassium within the bloodstream (hyperkalemia). These include: lisinopril, spironolactone, and amiloride. Doctors need to be aware of all medications and supplements that a person is taking.

  • Interactions: There are certain medications that suppress iodine uptake within thyroid tissue and reduce the the amount of thyroid hormones available to the body. These group of drugs include, iodide, iodide-containing preparations, amiodarone, nitroprusside, sulfonylureas, thalidomide, interleukin, lithium, perchlorate, and interferon-alpha, and can result in drug-induced hypothyroidism.

  • Medications that deplete iodine include, central nervous system drugs: SSRIs (e.g. Prozac, Zoloft) which can suppress thyroid function, or worsen hypothyroid conditions. 

  • Goitrogens: are naturally occurring dietary substances that can interfere with iodine uptake and hinder the manufacture of thyroid hormones within the cells of the thyroid gland. When the gland has difficulty synthesizing thyroid hormone, it can enlarge (causing goitre) in it's efforts to trap more iodine and compensate for inadequate levels of hormone production. For those already struggling with hypothyroidism they may need to be mindful of the quantity of raw goitrogenic foods they consume. However, goitrogens only become a risk factor when goitrogenic foods form a major part of the diet, or the diet is also deficient in iodine. Eating these foods in average amounts should pose little concern, and they are rich in other nutrients that benefit the thyroid gland and overall health.

  • Foods containing goitrogens like isothiocyanates and cyanoglucosides include, the brassica/cruciferous vegetables, such as, broccoli, cauliflower, cabbage, brussel sprouts, turnips, kale, spinach, radish, horseradish, bok choy, collard greens, rapeseed, and mustard greens. The cooking of these foods usually inactivates the goitrogens and lessens their negative effects, and therefore can be a part of a normal diet. Patients struggling with hyperthyroidism can eat these foods raw on a regular basis and this may help reduce thyroid hormone levels slightly, although this should not be considered a cure for an overactive thyroid gland.

  • High intake of millet, maize, strawberries, cassava, bamboo shoots, sweet potatoes, lima beans, almonds and walnuts may also contribute to an under-functioning thyroid gland if they are consumed regularly in large amounts. This would mainly be of concern for those already suffering with hypothyroidism or an iodine deficiency. 

  • Soy: Soy products, in particular, hinder iodine uptake and interfere with thyroid hormone synthesis. Soy is known to be an endocrine disruptor and may cause generalised hormonal imbalances in susceptible individuals. Soy can induce goitre and impair TPO activity, and despite its health benefits, has been implicated in the development of autoimmune thyroid disease. This raises concerns about the potential adverse side effects of soy-based infant formulas on the thyroid health of young children.

  • Interestingly, studies have found that countries who have a diet rich in iodine, like Japan and Korea, have the lowest rates of breast and ovarian cancers. Throughout the world, the rates of breast and other cancers tend to correlate with the population's levels of iodine within their body. However, some epidemiologic studies have shown that high daily seaweed intakes are associated with an increased risk of thyroiditis and certain types of thyroid cancer, although the exact mechanisms involved is unclear. Again, too little iodine is detrimental to health, and too much can cause problems. Balance is everything.


The importance of iodine for human health cannot be overestimated. This essential micronutrient keeps the thyroid gland fully functioning and producing the hormones that power every system in the body. Maintaining a healthy intake of iodine on a daily basis is vital, but at the same time a balanced intake needs to be found through food, and/or supplementation.

Within the thyroid community, the use of iodine and whether to supplement has been debated for decades. The finding: "One size does not fit all". Iodine does not cure all thyroid conditions, and should not be given to every patient, depending on the cause of their disease. Of course, iodine deficiency conditions can be corrected with iodine, but autoimmune thyroid diseases need a multifaceted approach regarding treatment, and for some, iodine supplementation may not be beneficial, but actually harmful.

Bottom line: maintain a healthy balanced diet including some iodine rich foods on a regular basis, work with a doctor, test your iodine levels before supplementation, research best sources of iodine to ensure potency and purity, be aware of bodily changes, and be regularly monitored with regards to any conditions and your general health.

Take care.


*Greenspan, Francis S., M.D. “The Thyroid and Iodine”. The Bridge, The Thyroid Foundation of America, Inc. Volume 13, No. 2, Summer 1998.
*“Hypothyroid” Natural Medical Protocols, Medical Software Solutions, 1998 – 2002. 

* “Goitrogens”. Food Chem Toxicol, Jun;33(6):537-43, 1995.
* Schachter, Michael, M.D. “The Diagnosis and Treatment of Hypothyroidism”. Intergrative Medicine, HealthWorld Online, 1996.
* “Levothyroxine Sodium”. HealthCentral RX, Mosby, Inc. 2000.

* Bartle, William, M.D. “Thyroid hormone drug interaction”. Thyrobulletin, Thyroid Foundation of Canada, Volume 20, No. 1, Spring 1999. Accessed March 2000.
* Ross, Douglas S., M.D. “Factors That Influence Levothyroxine Dose”. The Bridge, The Thyroid Foundation of America, Inc. Volume 12, No. 3, 1997.
* Shakir, K.M.Mohamed, M.D. “Ferrous Sulfate-Induced Increase in Requirement for Thyroxine in a Patient With Primary Hypothyroidism”. Case Report, 12 June, 1997. Accessed 30/08/00. 

* Turkington, Carol, Kaplan, Eliot, M.D. “Lithium”. Lycos Health with WebMD. WebMD Corporation, 1996-2000. Accessed 7/03/01.






© 2023 by Robyn Koumourou

Thyroid Disorders | Thyroid Matters

bottom of page