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Iodine and fortification

What is iodine?

Iodine is an essential nutrient for growth and development. Iodine occurs naturally in most foods, but usually in small amounts. Because iodine can’t be made in the body we need to get it from the food we eat. In New Zealand our soils are low in iodine and therefore New Zealand grown vegetables, fruits and grains have very low levels of iodine compared with food produced in other parts of the world. Even with a balanced diet it is difficult for New Zealanders to get enough iodine.

Why do we need iodine?

Iodine is important for our thyroid hormones. These hormones support normal growth and development in children and help to maintain the body’s metabolic rate. As iodine is essential for brain development, it is particularly important that unborn babies (foetus), infants and young children have enough iodine.

How much iodine is recommended?

It is recommended that New Zealand adults consume around 150 micrograms of iodine each day. Requirements are higher for pregnant and breastfeeding women and lower for children, infants and toddlers.

It is difficult to accurately assess how much iodine is being eaten in the diet, but results of NZFSA’s Total Diet Survey (2003/04) estimate the amount of iodine being eaten by New Zealanders may be less than 60 percent of what is recommended.

Life stage	Age	RDI (micrograms per day)	UL (micrograms per day)
Infants	0-6 months	..	..
	7-12 months	..	..
Children and adolescents	1-3 years	90	200
	4-8 years	90	300
	9-13 years	120	600
	14-18 years	150	900
Adults	19+ years	150	1100
Pregnancy	14-18 years	220	900
	19-50 years	220	1100
Breastfeeding	14-18 years	270	900
	19-50 years	270	1100

RDI = recommended dietary intake, UL = upper level of intake (Source: NHMRC & NZMoH, 2006)

Recommended Dietary Intakes for New Zealanders [Ministry of Health]

New Zealand Total Diet Survey 2003/04

What are important sources of iodine?

Foods that are important sources of iodine include reduced or low-fat milk and milk products, eggs, and seafood. Foods that contain seaweed such as sushi and seameal custard are also good sources. New Zealanders are generally recommended to reduce salt intakes but iodised salt will provide some iodine in your diet, if used instead of non-iodised salt in cooking or at the table. Most rock or sea salts sold in New Zealand contain very little iodine.

Low iodine levels in our diet may lead to health issues often referred to as iodine deficiency disorders. This might include poor growth and development in infants and children, thyroid diseases and goitre (swelling of the thyroid gland in the neck).

Iodine deficiency disorders are re-emerging

In New Zealand, like many other countries, iodine deficiency has led to health problems. In the late 1800s and early 1900s goitre was very common. In 1924 iodine was added to table salt to increase the iodine in people’s diets. The amount of iodine added to table salt was increased in 1938 and remains at a similar level today. This is believed to have contributed to a dramatic reduction in goitre in the middle of last century.

Recent studies have indicated that the iodine status of New Zealanders is declining to the point where the New Zealand Government has decided to replace non-iodised salt with iodised salt in most bread. This will contribute to helping to reduce the risk of iodine deficiency disorders affecting the New Zealand population. Low iodine status may be due to:

• people eating more commercially prepared foods (which tend to be made with non-iodised salt)

• a reduction in the use of iodine-containing sanitisers by the dairy industry. Cows’ milk and foods made from cows’ milk had higher levels of iodine when the dairy industry used disinfectants containing iodine during milk processing.

• less salt being used in home prepared foods because of health messages encouraging consumers to reduce their salt intake.

What is fortification?

Fortification is when extra nutrients (such as iodine) are added to food and drinks during the manufacturing process.

Mandatory fortification is when manufacturers are legally required to add extra nutrients (such as iodine) to a particular food to meet a significant health-need in the population.

Mandatory fortification of bread with iodine

In March 2008 Food Standards Australia New Zealand (FSANZ) introduced a food standard that requires the replacement of non-iodised salt with iodised salt in most bread. The food standard comes into effect in September 2009. Pizza bases, breadcrumbs, pastries, cakes, biscuits and crackers will not be required to contain iodised salt. To retain consumer choice, organic and unleavened bread will also be exempt from the replacement of non-iodised salt with iodised salt.

One of the reasons bread was chosen is because it is eaten widely by New Zealanders.

Replacing non-iodised salt with iodised salt in most bread is a simple and low cost way of helping to increase the iodine intake of most New Zealanders, and reduce the number of people who aren’t getting enough iodine.

Fortifying food with vitamins and minerals [FSANZ]

Is food that is fortified with iodine labelled?

Yes. For bread, the food label will list the use of iodised salt in the ingredients list.

Iodine, pregnancy and breastfeeding

Iodine is important for normal brain development, particularly for unborn babies (foetus), infants and young children. Pregnant and breastfeeding women need more iodine than the general population as they provide all of their baby’s iodine.

Replacing non-iodised salt with iodised salt in most bread will help to increase the amount of iodine pregnant and breastfeeding women will get in their diet, however, it is likely that most of these women still won’t get enough. Therefore, it is recommended to regularly choose foods that are naturally important sources of iodine, such as low-fat milk and milk products, eggs and seafood. Read NZFSA's ‘Food Safety in Pregnancy’ booklet on how to choose and safely prepare seafood and fish. Iodised salt will provide some iodine in your diet, if used instead of non-iodised salt in cooking or at the table.

The Ministry of Health has been working to secure a subsidised iodine-only tablet to help pregnant and breastfeeding women meet their extra iodine requirements. The Ministry of Health understands that a daily 150 microgram iodine-only tablet will be available later this year. Once the iodine-only tablet has been assessed and approved for supply it will be available to all pregnant and breastfeeding women as an over-the-counter pharmacy product.

Iodine supplements currently available in New Zealand (including seaweed and kelp) are not recommended for pregnant and breastfeeding women. The iodine content in some of these products is extremely variable and there are risks from having too much iodine. In the meantime, if there is concern about iodine intake, consultation with an appropriate health professional is recommended.

Food and Nutrition Guidelines for Healthy Pregnant and Breastfeeding Women (Ministry of Health)

Food Safety in Pregnancy

Iodine sensitivity

Exposure to large amounts of iodine has been shown to have an adverse reaction in certain individuals and this is referred to as ‘iodine sensitivity’. Often the symptoms are related to the non-iodine components of the substance causing the reaction, and not to iodine itself which is an essential nutrient.

There is concern that the replacement of non-iodised salt with iodised salt in most bread will negatively impact on these individuals.

A reaction however may only occur when iodine is consumed in very large amounts i.e. greater than 300 milligrams each day (equal to 300,000 micrograms). These amounts are much higher than what would be consumed in a typical diet with or without iodine fortified foods.

Monitoring iodine levels in the New Zealand population

From September 2009 the food standard requiring the replacement of non-iodised salt with iodised salt in most bread will be in place. The Ministry of Health and NZFSA have a joint role in monitoring the effectiveness of fortifying bread with iodine.

NZFSA will monitor iodine levels in the food supply and use this information to estimate how much iodine New Zealanders are eating.

National nutrition surveys conducted by the Ministry of Health can also 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. A new adult nutrition survey is currently underway and urine samples are being collected.

National nutrition surveys [Ministry of Health]

Related Links

Food Focus article on the importance of iodine in our diet

Media release: Mandatory iodine fortification

Updated 11 September 2009