AAS-National Committees

Iodine is a natural element found as a nutrient in our food. Iodised salt, dairy products, seafood, kelp, and eggs can all contribute to dietary iodine intakes. Of these, certain seafoods and kelp can contain very high levels of iodine. Iodine-containing supplements and medicines also contribute to iodine intakes for some people. Drinking water may also contribute to iodine intake, the level of contribution being dependent on the iodine concentration of the water supply for any given area.

What is the role of iodine in the body?

Iodine is essential for the production of thyroid hormones and thyroid health throughout life. Thyroid hormones regulate body temperature and metabolic rate in adults and children. These hormones are also very important for the normal development of the brain and nervous system before birth, in babies, and young children. It is therefore particularly important that pregnant women, breast-feeding mothers and young children have an adequate dietary iodine intake. When iodine requirements are not met, this results in low-levels of thyroid hormones in the blood. These low levels are primarily responsible for the series of functional and developmental abnormalities.

What are the effects of iodine deficiency?

In children iodine deficiency can impair the development of the brain and nervous system, with the most crucial period being from foetal development to the third year of life. Iodine deficiency leads to poor school performance, reduced intellectual ability and impaired work capacity. The most damaging disorders induced by iodine deficiency are irreversible mental retardation and cretinism. If iodine deficiency occurs during the most critical period of brain development, from the foetal stage up to the third month after birth, the resulting thyroid failure will lead to irreversible alterations in brain function. In adults iodine deficiency increases the risk of thyroid dysfunction in later life. Both adults and children are at risk of developing goitre, characterised by an enlarged thyroid gland.

Where is iodine deficiency a problem?

The problem of iodine deficiency is most severe in Africa and parts of Asia, while Europe only has moderate to severe deficiency (WHO 2004). In Australia recent studies indicate a re-emergence of mild-to-moderate iodine deficiency, resulting from inadequate iodine intake in New Zealand and in parts of Australia (Guttikonda et al 2003; McDonnell et al 2003).

As a result of the re-emergence of iodine deficiency in Australia and New Zealand the mandatory fortification of iodine is being considered by Food Standards Australia New Zealand (FSANZ). The proposal is to replace salt with iodised salt used in bread manufacturing with a salt iodisation range from 35 to 55 milligrams of iodine per kilogram of salt (FSANZ May 2007).

Why has there been a re-emergence of iodine deficiency?

Historically, people living in Tasmania, the Australian Capital Territory, New South Wales, Victoria and New Zealand had low iodine intakes. This has been attributed to the low iodine content of foods grown in the iodine deficient soils of these regions. In the past, various initiatives were put in place to address this problem, including supplementation and fortification schemes. The current deficiency is not fully understood but may be related to one or more of the following:

reduced use of iodine-based cleaning products in the dairy industry, leading to lower concentrations of iodine in milk; and
decreased consumption of iodised salt, due to greater use of non-iodised salt and a reduction in total salt intakes.

How much iodine do people need?

The values for adequate iodine intakes are set out in the Nutrient Reference Values for Australia and New Zealand (National Health and Medical Research Council 2006). The recommended dietary intakes (RDI[1]) for iodine for individuals are provided in Table 1.

	Age	RDI
		(mg per day)
Children and adolescents	1–3 years	90
	4–8 years	90
	9–13 years	120
	14–18 years	150
Adults	19+ years	150
Pregnancy	14–18 years	220
Pregnancy	19–50 years	220
Lactation	14–18 years	270
Lactation	19–50 years	270

Table 1. Australian and New Zealand recommended dietary intakes (RDI) for iodine

The proposed mandatory fortification would increase the average daily iodine intake of adults by around 30 to 70 micrograms.

What foods contain iodine?

Table 2 shows how much of a cross section of foods would need to be eaten to get and extra 50 micrograms of iodine into the diet. A range has been provided to account for natural differences of iodine content in foods.

Food	Amount required to gain an extra 50 mg iodine per day
Oysters or scallops	1–2
Salmon, canned	1–1.5 cans
Trim/low fat milk	2–3 cups
Tuna, canned	2–3 cans
Egg, boiled	2–4 eggs
Beef steak	8–10 steaks
Pasta, white, boiled	Over 2 kg

Table 2. Example of the amount of various foods required to add an extra 50 micrograms of iodine per day

Iodisation of salt

The World Health Organization (WHO) recommends iodisation of all salt as the main strategy for the control of global iodine deficiency. Iodisation of some or all food salt is common in many countries as the main or sole measure to address iodine deficiency. Iodised salt has been found to be a suitable substitute for non-iodised salt in the majority of foods tested (WHO 2004).

What is the extent of iodine deficiency in Australia and New Zealand?

Australia

Studies conducted over the last decade in New South Wales and Victoria, where approximately 60 per cent of the Australian population live, indicate the presence of mild-to-moderate iodine deficiency in all groups tested. Study participants included school children, adult volunteers, and pregnant and postpartum women. The results of the National Iodine Nutrition Survey (NINS) conducted during 2003 and 2004 in school-aged children in all states except Tasmania and the Northern Territory are shown in Table 3. These results suggest a significant proportion of the Australian population is currently affected by iodine deficiency, particularly in New South Wales (NSW) and Victoria, with median urinary iodine concentration (MUIC) for the total sample of 104 micrograms per litre, suggesting borderline iodine status.

State	MUIC (mg/L)	Iodine status
New South Wales	89.0	mild deficiency
Victoria	73.5	mild deficiency
South Australia	101.0	borderline optimal
Western Australia	142.5	optimal
Queensland	136.5	optimal
Total sample	104.0	borderline optimal

Table 3. Iodine status from the National Iodine Nutrition Survey (Li et al 2006)

The National Iodine Nutrition Survey findings are similar to those from studies on school-aged children from Melbourne, NSW and Tasmania (prior to implementation of the Tasmanian interim iodine supplementation program) which indicated mild deficiency (Guttikonda et al 2003; McDonnell et al 2003; Seal et al 2007).

Other studies conducted in recent years indicate various degrees of iodine deficiency amongst pregnant women in Melbourne and Sydney. (Burgess et al 2007; Chan et al 2003; Gunton et al 1999; Hamrosi et al 2005; Li et al 2001; Travers et al 2006). The MUIC in pregnant women is similar, if not lower, than the corresponding MUIC measured in school-age children in the same state.

New Zealand

The results of the 2002 New Zealand Children’s Nutrition Survey show that New Zealand children are mild-to-moderately iodine deficient, with deficiency greater in girls than in boys (Skeaff et al 2002). Research indicates a high proportion of New Zealand children have enlarged thyroid volumes, which is consistent with iodine deficiency (Skeaff et al 2003). Studies measuring iodine status in adults show that they are also deficient, especially pregnant women. Other published research indicates that breast-fed infants are moderately iodine deficient (Skeaff et al 2005). This also suggests that breast-feeding mothers, as a group, are also iodine deficient.

What defines iodine deficiency?

Moderate to severe iodine deficiency (population median urinary iodine concentration les than 50 micrograms per litre) has profound effects on intellectual development with the most extreme being cretinism. The health effects associated with mild iodine deficiency (population median urinary iodine concentration less than 100 micrograms per litre) have, in the past, been less easy to define as the outcomes are often sub-clinical. The term mild iodine deficiency is perhaps misleading as it does not convey the seriousness of the associated health effects.

A proposal to fortify salt with iodine

In Australia in May 2007, Food Standards Australia New Zealand (FSANZ) released a revised proposal (P230) for the mandatory fortification of salt with iodine for all salt used in bread manufacturing with a salt iodisation range from 35 to 55 mg of iodine per kilogram of salt.

This Proposal is now at the final assessment stage. Further policy advice relating to this proposal is being sought by the Ministerial Council. The health ministers from each state and territory are currently re-evaluating the evidence on the prevalence and severity of iodine deficiency in Australia.

Why choose to fortify salt with iodine in bread?

FSANZ’s dietary intake estimates indicate that 88 per cent of Australians aged 2 years and above consume bread. For New Zealanders aged 15 years and above, 87 per cent consume bread. International guidance and experience shows that using iodised salt is one of the best ways to reduce iodine deficiency. Further, there are only a handful of salt producers in Australia and New Zealand, making it easier to ensure effective quality control for iodine levels in salt. It would be more burdensome to require hundreds of bread manufacturers to determine the amount of iodine present in bread. Under this proposal, the main impact on bread manufacturers will be a requirement to replace salt with iodised salt, and changing the ingredient list to reflect this change.

Salt contributes to hypertension. There are efforts globally to encourage everyone to eat less salt. Therefore the substitution of iodised salt for salt in a widely eaten food is preferable to advising people to add iodised salt to their food. FSANZ are not proposing adding more salt to bread, just substituting the salt already used with iodised salt. Indeed, if manufacturers respond to calls from groups like World Action on Salt and Health to reduce the amounts of salt in their bread, we can easily increase the proportion of iodine in the lower quantities of salt.

Will everyone get enough iodine from bread?

It is unlikely that the mandatory use of iodised salt in bread manufacturing will deliver enough additional iodine to fully meet the needs of pregnant and breast-feeding women, whose requirements are substantially higher than the rest of the population. It is not possible to ensure these two groups receive sufficient iodine through fortification without also increasing iodine intakes in a large proportion of children above the upper level of intake[2].

Although fortification will increase the average intake of iodine for all sections of the population, except those who never eat bread, most pregnant and lactating women will benefit from taking an iodine supplement. While it is difficult to deliver enough iodine to meet the needs of pregnant and breast-feeding women through the use of iodised salt in bread, it is important to note that the majority of the population will receive sufficient additional iodine, including the majority of children and women of child bearing age. This will make it more likely for women to enter pregnancy with adequate iodine stores decreasing the risks of pregnancy affected by iodine deficiency.

Success in reducing iodine deficiency in Tasmania

In October 2001, a voluntary iodine fortification program was implemented in Tasmania. The baking industry was asked to substitute iodised salt for regular salt in bread. Post-intervention, cross-sectional urinary iodine surveys of Tasmanian schoolchildren aged 8 to 11 years were used to assess population iodine status and results were compared with pre-intervention survey. Median urinary iodine in post-intervention years (2003 to 2005) was significantly higher than in pre-intervention years, indicating that switching to iodised salt in bread resulted in a significant improvement in iodine status (Seal et al 2007). However a similar survey conducted in pregnant women failed to reduce iodine deficiency, indicating that it is likely that iodine supplements should be recommended for reproductive-age and pregnant women (Burgess et al 2007).

Acknowledgement

Significant bodies of text were taken directly from the Proposal P230 Consideration of the mandatory fortification with iodine (FSANZ May 2007).

References

Burgess JR, Seal JA, Stilwell GM, Reynolds PJ, Taylor ER, Parameswaran V. 2007. A case for universal salt iodisation to correct iodine deficiency in pregnancy: another salutary lesson from Tasmania. Med J Aust 186(11):574-576.

Chan SSY, Hams G, Wiley. V, Wilcken B, McElduff A. 2003. Postpartum maternal iodine status and the relationship to neonatal thyroid function. Thyroid: Official Journal Of The American Thyroid Association; 13:873-876.

FSANZ. May 2007. Proposal P230. Consideration of the mandatory fortification with iodine. Key issues for consideration at Final Assessment.

Guttikonda K, Travers C, Lewis P, Boyages S. 2003. Iodine deficiency in urban primary school children: a cross-sectional analysis. Med J Aust 179:346-348.

Gunton JE, Hams G, Fiegert M, McElduff A. 1999. Iodine deficiency in ambulatory participants at a Sydney teaching hospital: is Australia truly iodine replete? Med J Aust 171:467-470.

Hamrosi MA, Wallace EM, Riley MD. Iodine status in pregnant women living in Melbourne differs by ethnic group. 2005. Asia Pac J Clin Nutr 14:27-31.

Li M, Ma G, Boyages S, Eastman C. 2006. Re-emergence of iodine deficiency in Australia. Asia Pac J Clin Nutr 10:200-203.

McDonnell C, Harris M, Zacharin M. 2003. Iodine deficiency and goitre in schoolchildren in Melbourne, 2001. Med J Aust 178:159-162.

NHMRC. 2006. Nutrient Reference Values for Australia and New Zealand. Canberra.
http://www.nhmrc.gov.au/publications/synopses/n35syn.htm

Seal JA, Doyle Z, Burgess JR, Taylor R, Cameron AR. 2007. Iodine status of Tasmanians following voluntary fortification of bread with iodine. Med J Aust 186(2):69-71.

Skeaff SA, Ferguson EL, McKenzie JE, Valeix P, Gibson RS, Thomson CD. 2005. Are breast-fed infants and toddlers in New Zealand at risk of iodine deficiency? Nutrition 21(3):325-331.

Skeaff SA, Thomson CD, Gibson RS. 2002. Mild iodine deficiency in a sample of New Zealand schoolchildren. Eur J Clin Nutr 56(12):1169-1175.

Skeaff SA, Thomson CD, Gibson RS. 2003. Iodine Deficiency Disorders (IDD) in the New Zealand population: another example of an outmoded IDD control programme. Asia Pac J Clin Nutr 12 Suppl:S15.

Travers CA, Guttikonda K, Norton CA, Lewis PR, Mollart LJ, Wiley V, Wilcken B, Eastman CJ, Boyages SC. 2006. Iodine status in pregnant women and their newborns: are our babies at risk of iodine deficiency? Med J Aust 184:617-620.

WHO. 2004. Iodine status worldwide WHO Global Database on Iodine Deficiency.
http://whqlibdoc.who.int/publications/2004/9241592001.pdf

1. The average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97–98%) healthy individuals in a particular life stage and gender group.

2. The highest average daily nutrient intake level likely to pose no adverse health effects to almost all individuals in the general population. As intake increases above the UL, the potential risk of adverse effects increases.

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