Iodine is important for hormone development. It is found in dairy products, seafood, kelp, eggs, bread, some vegetables and iodised salt. A lack of dietary iodine can cause an enlarged thyroid gland (goitre) or other iodine deficiency disorders including mental retardation in children. Pregnant women need higher levels of iodine.
Iodine is found in a range of foods including dairy products, seafood, kelp, eggs, bread, some vegetables and iodised salt. Our bodies need iodine for the development of essential thyroid hormones. The thyroid is a gland in the throat that regulates many metabolic processes, such as growth and energy use. If you don’t have enough iodine in your diet, it can lead to an enlarged thyroid gland (goitre) or other iodine deficiency disorders.
Iodine deficiency is the world’s leading cause of preventable intellectual disability or mental retardation in children. All women who are pregnant, breastfeeding or considering becoming pregnant should ask their health professional for advice about their individual dietary needs.
Thyroid hormones regulate metabolism
The thyroid hormones regulate the body’s metabolic rate and promote growth and development throughout the body, including the brain. If there isn’t enough thyroid hormone circulating in the blood, the brain (via the pituitary gland) sends a chemical message (thyroid stimulating hormone) to the thyroid gland, which then releases a measured dose of these hormones.
The two main thyroid hormones, thyroxine and triiodothyronine, are synthesised from the amino acid tyrosine in combination with iodide. Thyroxine (T4) contains four iodine atoms and triiodothyronine (T3) contains three. If a person’s diet is too low in iodine, the thyroid gland gets larger and larger in an attempt to make more thyroid hormone. This overgrowth of the thyroid gland is called goitre.
Long-term deficiency can be serious
An enlarged thyroid gland, or goitre, isn’t the only side effect of not having enough iodine in the diet. If the deficiency is long term, hypothyroidism develops. Symptoms include dry skin, hair loss, fatigue and slowed reflexes.
Goitres can also increase the risk of thyroid cancer. Goitre can be associated with hyperthyroidism, a condition in which too much thyroid hormone is produced.
Iodine deficiency in babies and children
In the developing fetus, baby or young child, the effects of iodine deficiency are serious. They include stunted growth, diminished intelligence and retardation. Lack of iodine is a major problem in developing countries. It is the world’s number one cause of preventable intellectual disability in children. There is evidence that some levels of iodine deficiency may be too mild to cause goitre but may still retard brain development.
In Australia, studies conducted over the last decade in Victoria and New South Wales (where approximately 60 per cent of the Australian population lives) indicate the presence of mild-to-moderate iodine deficiency in all groups tested. Western Australia and Queensland appear to have adequate intakes, while South Australia is borderline.
Iodine fortification of bread in Australia
Since October 2009, iodised salt has replaced non-iodised salt in all bread sold in Australia (except organic bread). This is in line with the Food Standards Australia New Zealand (FSANZ) mandatory iodine fortification regulation, introduced to help address the re-emergence of iodine deficiency across most of the population. International guidance and experience have shown that using iodised salt is one of the best ways to reduce iodine deficiency and adding it to bread is the easiest way to add extra iodine to the food supply.
Bread fortified with iodised salt can provide enough iodine to avoid low thyroid activity for most people, without the need to add iodised salt to their diet. Salt contributes to hypertension (high blood pressure) and there are efforts globally to encourage people to eat less salt by avoiding adding salt in cooking and at the table.
How much iodine do we need?
The recommended daily intake (RDI) for iodine depends on your age and life stage. The amount we need is very small (around one teaspoonful over a lifetime for most adults) when compared to other nutrients and is measured in micrograms (mcg, or µg):
- Younger children (1 to 8 years) – 90µg
- Older children (9 to 13 years, boys and girls) – 120µg
- Adolescents (14 to 18 years) – 150µg
- Men – 150µg
- Women – 150µg
- Pregnancy and breastfeeding – 220µg and 270µg respectively.
Iodine intake in Australia has dropped
Low dietary levels of iodine were thought to be a problem in the past or in developing countries only. However, some researchers suspect that iodine intake levels in Australia have dropped considerably, perhaps by as much as half, over the past few decades. Ongoing research is underway to look at the problem and what might be done about it.
Some reasons for low iodine intake may include:
- Consuming most of our salt in processed foods as manufactures do not used iodised salt in processed foods (and, until recently, in bread)
- Less iodine in milk because of changes in treatment methods
- A possible reduction of iodine levels in Australian soils
- A reduction in the use of salt in cooking and table salt (particularly iodised salt).
How to get enough iodine in your diet
The best way to get the nutrients your body needs is as part of a healthy, well-balanced diet. Some suggestions to make sure you get the required daily amount of iodine include:
- Seafood – dietitians recommend two to three meals of seafood per week to get the beneficial fish oils. Eating fish twice a week will also provide most adults with enough iodine to fulfil their average iodine requirement.
- Bread – is now made using iodised salt in Australia. Organic breads and ‘no added salt’ breads are the only exceptions to this rule.
- Seaweed (kelp), dairy products and eggs – provide additional dietary sources of iodine.
- Some vegetables – may contain iodine, but only if they are grown in iodine-rich soils.
- Supplements – may be necessary if your dietary intake is inadequate. Many multivitamin capsules and tablets supply 100–150µg of iodine.
Pregnancy and iodine
Pregnant women need higher levels of iodine, as lack of this nutrient can retard normal development in a baby. Eating two serves of seafood each week will not be enough to meet a woman’s iodine requirements during pregnancy – you would need to eat almost nine cans of tuna a day to reach the recommended level (220mcg, or micrograms). In Australia, the National Health and Medical Research Council (NHMRC) recommends that all women who are pregnant, breastfeeding or considering pregnancy take an iodine supplement of 150mcg each day to make sure their needs are met.
If you are pregnant, breastfeeding or considering becoming pregnant, ask your registered medical doctor (GP) for advice about your individual daily needs. In particular, women with pre-existing thyroid conditions should not take iodine supplements until they have checked with their doctor.
Seafood is a valuable source of iodine, but pregnant women or women intending to become pregnant within the next six months should take care to avoid seafood that may contain large amounts of mercury. Mercury can be passed through the placenta and may affect the brain development of your baby. Some fish that contain high levels of mercury include shark, orange roughy, swordfish and ling.
Vegetarians can get iodine from bread, seaweed and some soymilks that include extracts of seaweed.
Where to get help
- Your doctor
- An Accredited Practicing Dietitian (APD)
Things to remember
- Dietary iodine is needed to make essential thyroid hormones.
- Not enough iodine in the diet can cause mental retardation and stunted growth in children and an enlarged thyroid gland (goitre) in adults.
- Good sources of iodine include bread fortified with iodised salt and any type of seafood, including seaweed.
- Young children should avoid eating salt added at the table or in cooking.
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Last reviewed: July 2011
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