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Iodine was one of the first trace-minerals to be identified as an essential nutrient. Nearly 5000 years ago, Chinese physicians treated goitre (enlarged thyroid gland in the neck) by feeding seaweed, seafood extracts and burnt sponge – we now know that these are all rich sources of iodine. In 1811, iodine was identified in seaweed in France, and 8 years later a Swiss physician named Dr Coindet used a burnt sponge and seaweed extract for the treatment of goitre, and reasoned that iodine could be the active ingredient in seaweed. In 1819, he tested tincture of iodine at 250 mg/day, in 150 goitre patients with great success. In the 1920s, iodine was shown to be an integral part of the thyroid hormone thyroxine (T4) and in 1952 triiodothyronine (T3).

Blank Woman with goitre Blank
Very low levels of iodine intake (less than 50µg/day) cause goitre, which presents as an enlarged thyroid gland. Other symptoms include dry skin, fatigue and hair loss.

The thyroid hormones T3 and T4 are required for the normal growth and development of essential organs including the brain and nervous system and have a broader role in the maturation of the body as a whole. They are important for energy production and oxygen consumption in all of our cells, helping to maintain the body’s metabolic rate. A typical adult body contains approximately 15–20mg of Iodine, of which 70–80% is in the thyroid gland (a butterfly-shaped organ located in the base of your neck) – which concentrates iodine. The rest is in our blood.

Iodine deficiency results in a range of conditions collectively termed iodine deficiency disorders. In severe deficiency, these have major effects on the developing foetus, such as abortion or stillbirth, congenital abnormalities, increased infant mortality, cretinism or mental deficiency with deaf mutism, spastic diplegia (a form of cerebral palsy), and even a form of dwarfism. In newborns, childhood or adulthood, iodine deficiency can lead to goitre or hypothyroidism as well as impaired mental and physical development. Paradoxically, excessive intakes of Iodine can also lead to the enlargement of the thyroid gland.

The iodine content of most foods is low and is affected by the soil, irrigation and fertilisers used. Losses can also occur in cooking (e.g., boiling). Best sources include:

  • Seafoods – fish (e.g. canned salmon), shellfish (e.g. oysters), and seaweed (e.g., sushi). 
  • Dairy – milk, yoghurt, cheese, etc. 
  • Bread – Australian and New Zealand bakers are required to use iodised salt in bread. 
  • Salt – Approximately 120 countries, including Canada and the USA, have adopted mandatory iodization of all food-grade salt. In Australia and New Zealand, it’s optional. While Iodine fortified salt contains high levels of iodine, use of iodised salt has reduced due to increased awareness of the association between high salt consumption and high blood pressure. 
  • Supplements – Pregnant and breast-feeding women may require iodine supplements, though consultation with a doctor is recommended before commencing. 

Finally, it’s important to note that our ability to utilise absorbed iodine is influenced by goitrogens in foods. Goitrogens are found in brassica vegetables such as cabbage, broccoli and Brussels sprouts and can interfere with the synthesis of the thyroid hormones T3 and T4. Similarly, foods that contain goitrogenic cyanoglucosides such as sweet potato and corn release thiocyanate that competes with iodine, blocking its uptake by the thyroid gland. This doesn’t mean that we should avoid these vegetables – just consume them in moderation as part of a healthy balanced diet.

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Dr Alan Barclay  
Alan Barclay, PhD is a consultant dietitian and chef (Cert III). He worked for Diabetes Australia (NSW) from 1998–2014 . He is author/co-author of more than 30 scientific publications, and author/co-author of  The good Carbs Cookbook (Murdoch Books), Reversing Diabetes (Murdoch Books), The Low GI Diet: Managing Type 2 Diabetes (Hachette Australia) and The Ultimate Guide to Sugars and Sweeteners (The Experiment, New York).

Contact: You can follow him on Twitter or check out his website.