Iodine and fortification

The New Zealand Food Safety Authority (NZFSA) and Ministry of Health (MoH) wishes to draw to the attention of New Zealand stakeholders that Food Standards Australia New Zealand (FSANZ) is due to release a Draft Assessment Report (DAR) on Iodine Fortification. The DAR on P230 Iodine Fortification will be available for comment during August 2006. This paper will consult the public on a proposal for mandatory fortification of the food supply with iodine to reduce the incidence of iodine deficiency in New Zealand and Australia.

As the consultation period will be short (4 weeks), those intending to make a submission are encouraged to be prepared for the release of the DAR. To assist those who wish to provide comment on the proposal, background information is provided below. NZFSA and MoH encourage all stakeholders to make submissions.

Why is iodine important and what happens if there is not enough in the diet?

Iodine is an essential nutrient for humans. Although only required in very small amounts, it is an important constituent of thyroid hormones. These hormones maintain the body’s metabolic state and support normal growth and development in children. As iodine is essential for normal brain development, it is particularly important that the unborn baby (foetus) and young children have adequate intakes.

The term iodine deficiency disorders is used to describe the wide range of effects low iodine status can have on health. One of the serious health effects of iodine deficiency disorders is goitre (enlargement of the thyroid gland). In very severe iodine deficiency, stunted growth and mental retardation can occur in children. A number of studies have reported adverse effects on hearing capacity, motor and cognitive function in children associated with moderate and severe iodine deficiency.

Is iodine deficiency an issue in New Zealand?

As in many other countries around the world, evidence of iodine deficiency has been observed in New Zealand and in the late 1800s and early 1900s goitre was very common. In order to decrease the incidence, table salt was iodised at a low level from 1924. However, this had little effect and the level was increased to 40-80mg of iodine per kilogram of salt in 1938. When iodised table salt was introduced there was a major public education campaign to ensure people understood the benefits of using iodised salt in the home. However, non-iodised salt has always been available in New Zealand as well as iodised table salt.

Recent evidence from a number of studies has indicated that the iodine status of New Zealanders is now declining to the point where intervention is again required to ensure that iodine deficiency disorders do not once again widely affect the New Zealand population. For example, a study by Skeaff (2005) of breast-fed infants showed that iodine levels were less than half of that of formula-fed infants, reflecting the low iodine concentration of breast milk due to the poor iodine status of breast feeding mothers. The 2002 National Children’s Nutrition Survey (Ministry of Health 2003) found that New Zealand children (aged 5-14 years) had mild iodine deficiency and that 28 percent of the children studied had low iodine status.

At the end of this document there is a list of publications that show the observations and research that demonstrate the extent of the current deficiency.

Why is there a re-emergence in iodine deficiency?

The re-emergence in iodine deficiency appears to be due to:

the increased consumption of commercially-prepared foods (manufactured mostly with non-iodised salt)

the declining use of iodine-containing sanitizers by the dairy industry

less salt being used in home prepared foods as a response to the health messages to reduce salt intake

Could we get sufficient iodine from the food we eat?

Dietary sources of iodine include seafood (fish, shellfish and seaweed), iodised salt, seameal custard, milk and eggs. The Ministry of Health’s Food and Nutrition Guidelines for Healthy Adults: A background paper (Ministry of Health, 2003) recommend choosing iodised salt when using salt, but do not recommend increasing overall salt intake.

The iodine content of vegetables, fruits and grains generally reflect the iodine level of the soil in which they were grown. The iodine content of New Zealand soils is low and as a consequence locally produced foods are also low in iodine.

Iodine levels of meat, chicken, eggs and dairy products are reflective of the iodine content of the animal feed used. Currently it is difficult for most consumers to obtain adequate iodine from their normal diet.

Should supplements containing iodine be recommended to consumers?

NZFSA and MoH recommend that supplementation with iodine should first be discussed with an appropriate health professional. While consumption of iodine containing supplements and kelp tablets will increase iodine intakes, care needs to be taken when considering supplementation as this may lead to an intake of iodine beyond the safe upper level of intake. The margin between too much and too little is very narrow and the iodine content in seaweed products and kelp tablets is extremely variable.

How is it proposed to increase the amount of iodine in the food supply?

Internationally the preferred option for increasing iodine levels in food is to ensure that all salt (including salt used in processed foods) is iodised. This is a simple and low cost way of increasing the iodine content of a range of foods. A proposal that considers the use of iodised salt in food manufacturing is being developed by Food Standards Australia New Zealand and will be available for public comment in August 2006.

Are there any complicating factors for consumers from increased iodine levels in food?

The effects of high iodine intakes on thyroid function are variable and depend on the health of the thyroid gland. Very high intakes (in excess of the established upper level of intake) of iodine may inhibit thyroid hormone production. A sudden increase in iodine intake in those used to very low intakes for prolonged periods of time can produce iodine-induced hyperthyroidism or thyrotoxicosis (thyroid poisoning). However, as it is unlikely that this would be an issue for the New Zealand consumer as the decline in iodine levels is relatively recent.

How will we know the effect of increasing iodine in foods?

It will be important that the effectiveness and any unexpected consequences of the standard are monitored. That can be done both by regularly checking the iodine content of foods and by measuring the iodine status of the population, in particular the most vulnerable groups within the population, such as children and pregnant women. For example the next round of the Total Diet Survey (TDS) to be conducted in 2008 will include iodine, and comparison of this survey to previous TDSs will provide valuable trend data.

A database of the iodine content of New Zealand foods is now available and will be regularly updated as new surveys are undertaken. Other surveys will analyse foods that are important sources of iodine in the diet and monitor where changes in animal husbandry practices and food processing may lead to changes in the levels of iodine. National Nutrition Surveys are also a tool which can be used to monitor the iodine status of the New Zealand population. For example, the 2002 National Children’s Nutrition Survey collected urine samples for measurement of urinary iodide, which indicates iodine status. The inclusion of assessment of urinary iodide excretion in the 2007/08 Adult Nutrition Survey is under consideration.

This information will allow the standard to be reviewed at regular intervals to assess the effectiveness of fortification in improving the iodine status of New Zealanders and for adjustments to the levels of iodine, if required to get the best outcome that is achievable.

You will be able to view the Iodine Fortification proposal (P230) at: once it is released in August.


Laurberg P. (2004) Victories and Challenges in Optimizing Iodine Intake. Thyroid 14, 589

Mann J, Aitken E. (2003) The re-emergence of iodine deficiency in New Zealand? New Zealand Medical Journal 351, 1161-1170

Ministry of Health. (2003) NZ Food: NZ Children. Key Results of the 2002 National Children's Nutrition Survey. Wellington. Ministry of Health

Ministry of Health. (2003). Food and Nutrition Guidelines for Healthy Adults: A background paper. Wellington Ministry of Health (refer for this and Food and Nutrition Guidelines for other life stages)

NHMRC (2006) Nutrient Reference Values for Australia and New Zealand including Recommended Dietary Intakes. Canberra: Department of Health and Ageing. Wellington: Ministry of Health

NZ Total Diet Survey

Skeaff S, Ferguson E, McKenzie J, Valeix P, Gibson R, Thomson S. (2005). Are breast-fed infants and toddlers in New Zealand as risk of iodine deficiency? Nutrition 21, 325-331.

Skeaff S, Thomson C, Gibson R. (2002) Mild iodine deficiency in a sample of New Zealand school children. European Journal of Clinical Nutrition 56, 1169-1175

Thomson C. (2004) Review article – Selenium and iodine intakes and status in New Zealand and Australia. British Journal of Nutrition 91, 611-672.

For more information, contact:

NZFSA: Charlotte Channer ( 04 463 2579

MoH: Elizabeth Aitken ( 04 495 4335.