The main function of iodine is to make thyroid hormones, which control metabolic processes (normal growth and development) and normal metabolic state (body temperature/metabolic rate).
The low levels of iodine present in the soil and environment in New Zealand are reflected in the low levels present in plant foods. This translates into a higher risk that people will suffer from iodine deficiency. Symptoms of deficiency are fatigue and swelling of the thyroid gland in the neck, called goitre. Low-iodine diets can retard children's mental and physical development and make people tired, overweight and constipated. In the 1920s salt was fortified with iodine as a way of tackling the goitre endemic occurring at the time.
Although today 70% of the salt used is iodised, many people have reduced their use of salt due to the risk of increased sodium intake leading to cardiovascular disease. People are also regularly eating more prepared meals or processed meals but the majority of the salt used in food industry is not iodised. The dairy industry has moved away from using cleaners which contained iodine. Rock salt which does not contain iodine, has also become more popular.
Food sources of iodine
Although it is advisable to limit salt intake, when using salt make sure it is iodised to ensure an adequate daily intake of iodine. Include other sources of iodine in the diet, such as seafood, fish, eggs and low-fat milk products. Supplements for iodine should only be used if recommended by a health professional, as high levels of iodine can be toxic and lead to adverse health effects.
New regulations were introduced in September 2009 making it mandatory to replace non-iodised salt with iodised salt in all breads except organic and unleavened breads in a bid to address New Zealand’s problem of mild-moderate iodine deficiency. Pizza bases, breadcrumbs, pastries, cakes, biscuits and crackers are not required to contain iodised salt. To retain consumer choice, organic and unleavened bread are also exempt from the replacement of non-iodised salt with iodised salt.
One of the reasons bread was chosen as the food to be fortified with iodine 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.For bread, the food label will list the use of iodised salt in the ingredients list.
Monitoring iodine levels in the New Zealand population
The Ministry of Health and Ministry for Primary Industries (MPI) have a joint role in monitoring the effectiveness of mandatory fortification of bread with iodine.
MPI is responsible for monitoring iodine levels in the food supply and can use this information to estimate how much iodine New Zealanders are eating.
In 2010, MPI conducted its first post-fortification analytical survey of the iodine levels in over 500 breads. Results of this survey found that most breads (excluding organic and unleavened breads) now contain iodine from the mandatory replacement of salt with iodised salt. The iodine levels of bread were used to estimate iodine intakes in children 5 – 14 years of age post-fortification. It was found that the percentage of New Zealand children estimated to have inadequate iodine intakes has dropped from 38 to 4 percent because of iodine fortification.