Iodine is a chemical element, naturally occurring in seawater. In the human body, iodine is key component of thyroid hormones.

Iodine deficiency

Although iodine is needed only in very small amounts, a deficiency can lead to serious health problems. Severe iodine deficiency results in impaired production of thyroid hormones.

The thyroid is a butterfly-shaped gland located at the base of the neck that secretes thyroid hormones, and is responsible for metabolism, growth, development, and reproductive function. Since iodine is an essential nutrient for normal thyroid function, deficiency can lead to thyroid disorders, including:

• Goitre - an enlargement of the thyroid gland, which may cause symptoms such as choking, especially when lying down, and difficulty swallowing and breathing.
• Hypothyroidism - a deficiency of thyroid hormone. Symptoms include fatigue, dry skin, sensitivity to cold, and depression.
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• Pregnancy-related problems – pregnancy increases thyroid activity and hence iodine requirements. Severe iodine deficiency in women who are pregnant or lactating can lead to miscarriages and to a condition in their infants called cretinism, of severe physical and mental retardation. In fact, iodine deficiency is the world’s greatest single cause of preventable brain damage, mainly in countries in central Africa, South East Asia, and the Middle East.

How do I know if I am deficient?

If you suffer from a visible enlarged thyroid gland (goitre) or symptoms of underactive thyroid (hypothyroidism), it is possible that you are not consuming enough iodine in your diet. However, you may be deficient in iodine without showing any symptoms. According to the Australian Thyroid Foundation, the most reliable way to check your iodine levels is by having a urine test, since iodine is excreted via the urine. You can also ask your doctor to check the levels of thyroid hormones n your blood.

Iodine fortification

In 2009, In order to address mild iodine deficiency, Australia and New Zealand, among other countries, introduced mandatory replacement of non-iodised salt with iodised salt for making all breads except organic bread and bread mixes for making bread at home.

Iodised salt is basically table salt with added iodine in the form of potassium iodide. In fact, salt iodisation has been implemented in more than 120 countries around the world. Australian manufacturers also have the option of using iodised salt in other foods but it must be listed in the ingredient list of food labels. Not all table salt is iodised.

Food sources of iodine

• Cheese
• Cows milk
• Eggs
• Frozen Yogurt
• Ice Cream
• Iodized table salt
• Saltwater fish
• Seaweed (including kelp, dulse, nori)
• Shellfish
• Soy milk
• Soy sauce
• Yogurt

Other sources of iodine

Since iodine has the ability to kill germs, it is used in wound dressing, antiseptic liquids for topical application in the treatment of wounds, surgical scrubs, and sore throat gargle. Iodine is also used in injections of contrast medium in medical X-ray imaging.

Iodine supplements

Iodine supplements are usually available in the form of potassium iodide that comes as liquid drops, oral spray, or kelp capsules/tablets. Kelp is a type of seaweed naturally rich in iodine. In addition, iodine can be found in combination products, such as multivitamin/mineral supplements, pregnancy formulas and thyroid supplements.

Who may need iodine supplements?

Most Australians consume sufficient iodine in their diets, but deficiency still exists, especially among the following groups:

• Pregnant women and school children. In Australia, school children and pregnant and breastfeeding women have been shown to suffer from mild to moderate iodine deficiency. The Department of Health advises women who are pregnant to take an iodine supplement of 150 micrograms each day. Women with pre-existing thyroid conditions should seek advice from their medical practitioner before taking a supplement. Children should consume iodine only through their diet unless prescribed by a doctor.
   
• Individuals who do not eat iodine-food sources. You may be iodine-deficient if you are on a low salt diet and do not eat bread or seafood. If you are in any doubt consult your doctor. In some cases, replacing non-iodised salt with iodised salt may be sufficient to increase the level of iodine in your body. However, some people may still need supplemental iodine.

Goitrogens

Certain foods contain substances that interfere with iodine utilisation or production of thyroid hormones, resulting in an increased need for iodine; these substances are called goitrogens.

Foods that are high in goitrogens include soy, millet, sweet potatoes, and cruciferous vegetables like cabbage, broccoli, Brussels sprouts, cauliflower, bok choy, and kale. Goitrogens may be harmful for your thyroid only when consumed in excessive amounts or if there is already a coexisting iodine deficiency. However, there is no need to eliminate them entirely from your diet as they have many other beneficial properties.

If you have thyroid problems, limiting the consumption of these foods to 3-6 servings per week, as well as eating them cooked and not raw (steamed or boiled) significantly reduce goitrogens levels.

Can I take too much iodine?

Taking too much iodine can be harmful. Excessive iodine intake by people who are not deficient may result in hypothyroidism. At the same time, individuals who are iodine-deficient and take too much iodine are at risk of developing hyperthyroidism, which is an overproduction of thyroid hormones. Symptoms of hyperthyroidism include weight loss, tachycardia (rapid heart rate), muscle weakness, and skin warmth.

Patients with renal impairment, as well as those who take warfarin, lithium, or have pre-existing thyroid problems, should always consult with their doctor before taking any iodine supplements.

Some individuals are sensitive to high levels of iodine, both in food and iodine-based antiseptics. If you have been found to be sensitive to iodine, you may be prescribed a low-iodine diet.

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References

American Thyroid Association, Iodine Deficiency 2014. Available at: https://www.thyroid.org/iodine-deficiency

Australian Government Department of Health 2013. Nutritional supplements. Available at: http://www.health.gov.au/internet/publications/publishing.nsf/Content/clinical-practice-guidelines-ac-mod1~part-b~lifestyle-considerations~nutritional-supplements

De Benoit, B., Mclean, E., Andersson, M., & Rogers, L. 2008. Iodine deficiency in 2007: Global progress since 2003. Food and Nutrition Bulletin, 29(3). Available at: http://www.who.int/nutrition/publications/micronutrients/FNBvol29N3sep08.pdf

Food Standards Australia New Zealand 2016. Iodine fortification. Available at: http://www.foodstandards.gov.au/consumer/nutrition/iodinefort/Pages/default.aspx

Food Standards Australia New Zealand 2016. Iodine in food and iodine requirements. Available at: http://www.foodstandards.gov.au/consumer/nutrition/iodinefood/pages/default.aspx

Food Standards Australia New Zealand 2016. Iodine sensitivities. Available at: http://www.foodstandards.gov.au/consumer/nutrition/iodinesensitive/pages/default.aspx

Lee S. L.Iodine deficiency 2017. Medscape. Available at: https://emedicine.medscape.com/article/122714

 Linus Pauling Institute - Oregon State University, 2015. Iodine. Available at: http://lpi.oregonstate.edu/mic/minerals/iodine#reference5

The Australian Thyroid Foundation - Iodine deficiency & Nutrition 2018. Available at: https://www.thyroidfoundation.org.au/page/13/iodine-nutrition-iodine-deficiency

University of Maryland Medical Center 2007. Possible Interactions with: Iodine. Available at: http://www.umm.edu/health/medical/altmed/supplement-interaction/possible-interactions-with-iodine