Iodine is a chemical element, like oxygen and iron. It occurs naturally in the sea and in some soils.
Iodine is also found in marine life (including fish, prawns and seaweed), some plants grown in iodised soil, and in the products of animals that have grazed on soil with iodine in it. It’s added to some foods, such as salt and most bread.
Why we need iodine
Our thyroid glands need iodine to produce the hormones that control metabolism, growth and development.
If children and grown-ups don’t get enough iodine in their diets, they might become iodine deficient. Iodine deficiency can cause the thyroid gland to increase in size. An enlarged thyroid gland, or goitre, can:
- affect hormone production
- cause swallowing and breathing difficulties
- lead to hypothyroidism, which can cause problems such as weight gain, tiredness, intolerance to cold and depression
- result in stunted growth.
Iodine and pregnancy
During pregnancy, a woman’s thyroid gland has to work extra hard. This is because the hormones it produces help the growth of her fetus’s brain and nervous system. After birth, these hormones are delivered to the baby through breastmilk, which keeps the brain and nervous system developing.
Severe iodine deficiency in a pregnant or breastfeeding woman might lead to brain damage in a fetus or baby. If you’re pregnant and worried about your iodine intake, your doctor can use a simple urine test to check your levels.
Pregnant and breastfeeding women might need iodine supplements and should consult their doctor or an accredited practising dietitian for individual dietary advice.
Sources of iodine
To ensure that you and your children are getting enough iodine, include the following in your family’s diet each week:
- Packaged bread – note that organic bread, salt-free bread and bread mixes for making bread at home might not contain iodine, so either check the ingredient list or ask at the point of sale.
- Seafood – but be careful when selecting fish for your children or for yourself if you’re pregnant. Some fish – such as flake, swordfish and barramundi – contain higher levels of mercury than others. You shouldn’t eat them often.
- Eggs, meat, vegetables and dairy products – if you don’t eat animal products, you might need iodine supplements.
- Iodised table salt (not sea salt) rather than regular salt – this is a rich source of iodine, with 25-65 micrograms of iodine per gram of salt.
How much iodine do we need?
The Nutrient Reference Values for Australia and New Zealand recommend the following daily intake of iodine.
Why some people don’t get enough iodine
||Examples of what and how much to eat
|Young babies (0-6 months)
||Breastmilk or infant formula
|Older babies (7-12 months)
||Breastmilk or infant formula
|Children (1-8 years)
||2 cups milk, or 1.5 cups milk and 1 egg
|Children (9-13 years)
||2 cups milk, 2 slices bread (with added iodised salt) and 1 egg
|Teenagers (14-18 years) and adults
||4 slices bread (with added iodised salt), 1 egg, 1 cup milk and 1 fish fillet
Some Australian children – especially those in Victoria, Tasmania and New South Wales – don’t get quite enough iodine. This is thought to be because several areas of Australia might have low iodine levels in the soil, meaning vegetables from these areas provide little iodine.
Many families now also cut salt completely out of their diets, leading to lower iodine levels. Even when salt is added to their meals, it’s often in the form of regular salt or sea salt, rather than iodised table salt.
Too much iodine is dangerous
It’s possible to have too much iodine, but consuming a dangerously high level of it is actually quite difficult. For example, your child would need to eat 1 kg of mozzarella or 25 whole boiled eggs, or drink five glasses of milk in one sitting to have too much.
Some people are more sensitive to excessive iodine intake, which might cause difficulties with their thyroids. Some medications and supplements might also contain high doses of iodine. If you’re concerned about your own or your child’s iodine intake, see your doctor or an accredited practising dietitian.