Iodine Deficiency in the New Zealand Diet
We are not getting enough iodine from our diet because foods grown in New Zealand soils are low in iodine. Low iodine levels in our diet may lead to health issues such as poor growth and development in children, thyroid diseases and goitre. Food Standards Australia New Zealand (FSANZ) is looking at the possibility of fortifying bread with iodine (using iodised salt) to overcome this deficiency.
Why iodine is important
Iodine is an essential nutrient for humans.
Although only required in very small amounts, iodine is important for 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 unborn babies and young children have enough iodine.
Sources of iodine in our diet
Foods that are rich in iodine include seafood (fish, shellfish and seaweed), iodised salt, seameal custard, milk and milk products, and eggs.
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 from the food they eat.
New Zealand’s history of iodine deficiency
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.
Iodine deficiency is re-emerging
The re-emergence of iodine deficiency appears to be due to:
• people eating more commercially prepared foods (which tend to be made with non-iodised salt)
• reduction in the use of iodine-containing sanitizers by the dairy industry. We used to get small amounts of iodine in cows milk when the dairy industry used disinfectants containing iodine
• less salt being used in home prepared foods because of health messages encouraging consumers to reduce their salt intake.
The Ministry of Health recommends choosing iodised salt when using salt, but does not recommend increasing overall salt intake.
Food and nutritional guidelines for Healthy adults can be obtained from the Ministry of Health
Some New Zealand children are now showing signs of mild iodine deficiency. Further intervention is being considered to ensure iodine deficiency disorders do not widely affect the New Zealand population.
Results of the 2002 National Children’s Nutrition Survey indicate the presence of mild iodine deficiency amongst 5-14 year old children in New Zealand. Twenty eight percent of the children studied had low iodine levels.
Our diet is unlikely to provide sufficient iodine
Results of our Total Diet Survey (2003/04) estimated the iodine intake of New Zealander's is at best only 57 percent of the recommended dietary intake.
It is difficult to get enough iodine from a normal New Zealand diet, even by eating naturally iodine-rich foods such as milk and milk products, eggs, meat, and seafood. We also get some iodine from seaweed products although the amount is highly variable. Infants and toddlers tend to get their iodine from baby foods, milk and milk products. Meat from farmed animals may be higher in iodine if they are fed on supplementary feeds, which have added iodine.
Iodine supplements and the risks of getting too much iodine
Ministry of Health and NZFSA 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 intake, you need to take care not to take more than the recommended safe upper level. The iodine content in seaweed products and kelp tablets is extremely variable.
The effects of high iodine intake on thyroid function are variable and depend on the health of your thyroid gland.
Getting too much iodine from your food however, is an unlikely problem in New Zealand as you would need to eat far more than the recommended dietary intake of iodine for prolonged periods to be affected.
Overcoming a lack of iodine in the New Zealand diet
Internationally the preferred option for increasing iodine levels in food is to ensure 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.
FSANZ are in the process of developing a new food standard. If introduced, this new standard may require all salt used in the manufacture of bread (excluding organic and unleavened breads) to be iodised.
Monitoring iodine levels in the New Zealand population
If a new food standard affecting iodine levels is brought in, it will be important to monitor the:
• health of New Zealanders in relation to iodine
• dietary intake of iodine, and
• iodine levels in the food supply.
Some monitoring is already underway. For example, the 2008 round of the Total Diet Survey (TDS) will include iodine. Comparison of the 2008 survey to previous TDSs will provide valuable trend data.
The database of the iodine content of New Zealand foods will be updated as data is collected. 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 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. The inclusion of urinary iodide excretion assessment in the 2007/08 Adult Nutrition Survey is under consideration.
Survey information will allow any new standard to be reviewed at regular intervals. This would help us assess whether adding iodised salt in bread improves the iodine status of New Zealanders. Monitoring will also help pinpoint the need for any adjustments to the levels of iodine in food if required.
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Contact for enquiries
New Zealand Food Safety Authority
68-86 Jervois Quay
PO Box 2835