Iodine in our bread

In 2009 the New Zealand government approved a plan to fortify our bread with iodine with the use of iodised salt in the ingredients (except for organic and salt-free breads and some home-bake bread mixes).

Why we need iodine

Our bodies need iodine to work properly. Iodine is an important ingredient of our thyroid hormones, which control our metabolism, growth and development. It is also very important for brain development in babies in the womb and young children. As for making sure you eat your sandwiches, researchers from Otago University have shown that correcting mild iodine deficiency in children improves their intelligence.

Iodised salt in bread

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Since 2009, under the Australia New Zealand Food Standards Code, bakers must use iodised salt in bread and bread products. The only exceptions are organic bread, non-yeast-leavened bread and bread mixes.

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New Zealanders are increasingly deficient in iodine

Research has shown that many New Zealanders were becoming increasingly deficient in iodine. The reasons for this include:

• changes to diet over the last few years (less iodised salt being consumed, less seafood, fewer eggs)

• changing practices in the dairy industry

• low levels of iodine in New Zealand soils (meaning that our fruits, vegetables and grains have low iodine content).

“In the past, most of our iodine came from dairy foods such as milk and cheese, and iodised salt used at the table or in cooking. But today people are adding less salt to food or are replacing iodised salt with rock or sea salt that contains virtually no iodine. Many people are not aware that the salt used to make foods bought in the supermarket (i.e. processed foods) is not iodised. And although fish and seafood are rich in iodine, most New Zealanders do not eat enough of these foods to get much iodine from them. At present, most children and adults, especially pregnant and lactating women, are iodine deficient,” says Dr Sheila Skeaff, Senior Lecturer at the Department of Human Nutrition, University of Otago. “People who do not eat commercial breads should ensure that they obtain additional iodine from consuming more iodine-rich foods or taking an iodine-containing supplement. The use of kelp tablets, however, is not recommended, as these tablets often contain variable and very high amounts of iodine.”

The consequences of iodine deficiency

Professor Christine Thomson, also from the Department of Human Nutrition at the University of Otago, says that researchers at Otago identified the re-emergence of mild iodine deficiency in New Zealand in the early 1990s, in spite of adequate iodine status reported during the 1960s–1980s. “Subsequent research by us indicated that the low iodine status is being reflected in disturbances in thyroid hormone metabolism, enlarged thyroid glands (goitre) and more recently a possible impairment in cognitive function of children. This situation is likely to worsen unless measures are taken to increase our iodine status.”

Goitre

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Goitre, which is an enlargement of the thyroid gland, is usually caused by lack of iodine in the diet.

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Lyn Gillanders, a Senior Clinical Dietician at the New Zealand Dietetic Association, says that, worldwide, iodine deficiency is the biggest single cause of preventable brain damage and mental retardation. “In New Zealand, evidence from the 2002 National Children's Nutrition Survey was that New Zealand children had urinary iodine excretion rates consistent with mild iodine deficiency. [This is the best way of measuring iodine status.] It's an issue in New Zealand because the consequences might be that children do not learn and develop as well as they might do. The effects of deficiency are seen at all stages of development but the other vulnerable time would be foetal development and when being breastfed.”

The Ministry of Health worked to secure a subsidised iodine-only tablet to help pregnant and breastfeeding women meet their extra iodine requirements. The option of a daily 150 microgram iodine-only tablet is now available for all pregnant and breastfeeding women as an over-the-counter pharmacy product (or at a lower cost when prescribed by a midwife, medical practitioner or nurse practitioner) and is recommended by the Ministry of Health.