Iodine

Iodine is essential nutrient and is required for regulating metabolism through its role in thyroid function. Iodine is essential for the normal development of the brain and nervous system especially during pregnancy and the first three years of life. The Australian and New Zealand food supply has insufficient iodine and so most bread is now required to be made with iodised salt.

WHAT IS IODINE?

Iodine is an essential trace element that our bodies need for normal growth and development1. It is mainly found in the ocean and the soil – although in quite small concentrations. We get our iodine from the plants and animals we eat. How much depends on the concentration of iodine in the soils in which they were grown. The most potent source of iodine in our diet is ocean fish and other seafood. In countries such as Australia and New Zealand, the soils are iodine depleted and, as a result, so are our vegetables, grains and grazing livestock.

WHAT DOES IODINE DO?

  • Iodine is an essential micronutrient in the human diet.
  • Its most important known function is as a component of thyroid hormones. Thyroid hormones are produced by the thyroid gland (located at the base of the neck).
  • Thyroid hormones play a vital role in regulating metabolic processes such as growth and energy expenditure. They are essential throughout childhood for normal brain and physical development. Overseas studies have shown that children with low iodine levels may have their hearing, coordination and alertness affected. Mild iodine deficiency can impair development and cause subtle deficits in intelligence. These problems are reversible in very young children which is why it is important for babies to be born with adequate iodine levels and to have the recommended intake of iodine in their early years.
  • Iodine is also critical for normal development of babies in the womb. Pregnant women, or women who plan to become pregnant, should ensure their iodine intake is satisfactory. If you are planning a pregnancy discuss an iodine supplement as well as a folate supplement with your doctor.

WHICH FOODS ARE SOURCES OF IODINE?

Recent studies have shown that many people in Australia and New Zealand do not obtain enough iodine from the foods they eat.

The foods which contribute most iodine to the Australian diet are dairy foods, sea foods, kelp and eggs. All infant formula is required to be supplemented with iodine.

Iodised salt also contributes iodine to the diet, but adding extra salt is not the solution for most Australians who may already be consuming more salt than they need. Some foods like bread are moderately high in salt and as iodised salt is now required to be used in bread, it also becomes a source of iodine. Australia and New Zealand now uses iodised salt in bread and this will increase the average iodine intake. Organic bread and breads made from non wheat flour will not be supplemented and if you eat these breads you will need to seek out other foods which are good sources of iodine and/or take an iodine supplement. Other Foods containing iodised salt should show that the salt is iodised on the ingredient listing on the label.

The following table of food sources is indicative as the amount of iodine will depend on where the food was grown.

FOOD Micrograms of iodine per 100g
Oysters 160
Sushi (containing seaweed) 92
Canned salmon 60
Bread (with added iodised salt) 46
Steamed snapper 40
Cheddar cheese 23
Eggs 22
Ice Cream 21
Chocolate milk 20
Flavoured yoghurt 16
Regular milk 13
Canned tuna 10
Beef, pork, lamb <1.5
Apple, orange, grapes, banana <0.5

HOW MUCH DO YOU NEED?

A teaspoon of iodine is all a person requires in a lifetime. However, the thyroid gland does not have the capacity to store this amount, so small amounts of iodine must be consumed regularly in the diet.

Recommended Intake1

Age Adequate Intake Per Day (AI) Micrograms Recommended Dietary Intake Per Day (RDI) Micrograms
0-6 months 90
7-12 months 110
1-3 years 90
4-8 years 90
9-13 years 120
14-18 years 150
> 18 years 150
Pregnant women 220
Lactating women 270

IS IT POSSIBLE TO HAVE TOO MUCH?

There are upper limits for iodine consumption; however, these are not usually a concern for most healthy people. Consultation with a doctor or healthcare professional is recommended before taking any supplements, especially if you have a diagnosed thyroid condition.

...OR TOO LITTLE?

Recent evidence has shown that the consumption of iodine is declining in Australia. 50% of children and pregnant or breastfeeding women living in Australia have been shown to be iodine deficient A study of new born babies in Victoria showed an increase in the number of babies who were deficient in iodine from 2001 to 2006 and the researchers suggest that assessment of iodine levels should become part of the standard health assessments performed on new babies in Australia.

This fact sheet contains general information and is not intended as a substitute for medical advice. Please consult your healthcare professional for specific advice for your personal situation.

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REFERENCES

Source: Nutrient Reference Values. 2006. Australian National Health and Medical Research Council (NHMRC) and the New Zealand Ministry of Health (MoH).

FSANZ Advice Pregnant Women. Available at http://www.foodstandards.gov.au/consumerinformation/pregnancyandhealthyeating/

FSANZ; Fact Sheet: Mandatory Iodine Fortification July 2009. www.foodstandards.gov.au/scienceandeducation/factsheets

Mu Li, Kay V Waite, Gary Ma and Creswell J Eastman. Declining iodine content of milk and re-emergence of iodine deficiency in Australia Med J Aust 2006; 184 (6): 307. Eastman CJ. Iodine supplementation: the benefits for pregnant and lactating women in Australia and New Zealand. Obstet Gynecol 2005; 7: 65-66

Ciara M McDonnell, Mark Harris and Margaret R Zacharin. Iodine deficiency and goitre in schoolchildren in Melbourne, 2001 Med J Aust 2003; 178 (4): 159-162.

Mu Li, Creswell J Eastman, Kay V Waite, Gary Ma, Margaret R Zacharin, Duncan J Topliss, Philip E Harding, John P Walsh, Lynley C Ward, Robin H Mortimer, Emily J Mackenzie, Karen Byth and Zelda Doyle. Are Australian children iodine deficient? Results of the Australian National Iodine Nutrition Study Med J Aust 2006; 184 (4): 165-169

Eastman CJ. Iodine supplementation: the benefits for pregnant and lactating women in Australia and New Zealand. Obstet Gynecol 2005; 7: 65-66.

Travers CA, Guttikonda K, Norton CA, Lewis PR, Mollart LJ, Wiley V, Wilcken B, Eastman CJ, Boyages SC. Iodine status in pregnant women and their newborns: are our babies at risk of iodine deficiency? Med J Aust. 2006 Jun 19;184(12):617-20.

Gisselle Gallego, Stephen Goodall and Creswell J Eastman Iodine deficiency in Australia: is iodine supplementation for pregnant and lactating women warranted? MJA 2010; 192 (8): 461-463

Zimmermann MB Iodine deficiency in pregnancy and the effects of maternal iodine supplementation on the offspring: a review. Am J Clin Nutr. 2009 Feb;89(2):668S-72S. Epub 2008 Dec 16.

Rahman A et al. Increased iodine deficiency in Victoria, Australia: analysis of neonatal thyroid-stimulating hormone data, 2001 to 2006 MJA 2010; 193 (09): 503-505

Zimmermann MB. Iodine deficiency. Endocr Rev. 2009 Jun;30(4):376-408. Epub 2009 May 21