Iodine: what is it?

Iodine is an essential nutrient for humans. It’s important for growth, development and good health, but we only need a small amount of it.

Iodine 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 iodine-rich soil, and the products of animals that have grazed on soil with iodine in it.

Iodine is added to some foods, like salt and commercially baked bread.

Why we need iodine

The thyroid gland needs iodine to produce the hormones that control metabolism, growth and development.

If people don’t get enough iodine in their diets, they might develop iodine deficiency. This can cause the thyroid gland to work harder and increase in size. An enlarged thyroid gland, or goitre, can cause swallowing and breathing difficulties.

Iodine deficiency can also lead to:

• hypothyroidism, which can cause problems like weight gain, dry skin, hair loss, tiredness, intolerance to cold and depression
• stunted growth and intellectual impairment.

Iodine, pregnancy and breastfeeding

During pregnancy, the thyroid gland has to work extra hard. This is because the hormones it produces help the growth of the unborn baby’s brain and nervous system.

Because their thyroid glands are working harder, pregnant women need extra iodine so they don’t become iodine deficient.

Severe iodine deficiency in pregnant women might lead to miscarriage, stillbirth or intellectual disability in babies.

After birth, breastfed babies depend on breastmilk as a source of iodine, which keeps their brains and nervous systems developing. This means that iodine deficiency in breastfeeding mothers can also be a risk for babies.

If you’re pregnant, trying to become pregnant, or breastfeeding, it’s recommended that you take an iodine supplement of 150 micrograms (μg) per day. If you have any pre-existing thyroid problems, check with your doctor before taking a supplement.

Most pregnancy supplements contain iodine. Check your pregnancy supplement ingredients to make sure you’re getting the recommended amount of iodine per day. You can also ask your doctor or midwife about your iodine needs.

Kelp and seaweed iodine supplements aren’t recommended because their iodine content varies.

Sources of iodine

If you include the following foods in your family’s diet each week, it’ll help to ensure that you and your children are getting enough iodine:

• Packaged bread: bread fortified with iodine can usually give your family enough iodine. Note that organic bread, salt-free bread, unpackaged bread, and bread mixes for making bread at home might not contain iodine, so either check the food label or ask at the point of sale.
• Seafood: experts recommend 2-3 meals of seafood per week. Tinned salmon and seaweed are the best food sources of iodine. If you’re pregnant, you should be careful when choosing fish. Some fish – like flake, swordfish and tuna – have higher levels of mercury than others.
• Eggs and dairy products: note that the amount of iodine in these foods varies.
• Fruit and vegetables: these contain small amounts of iodine and are important for a healthy diet.
• Meat: this contains small amounts of iodine.

Vegans might also need to consider iodine supplements or iodine-rich vegan foods like fortified soy milks.

Iodised salt is a rich source of iodine and has replaced non-iodised salt in all packaged breads sold in Australia. Bread fortified with iodised salt can provide enough iodine for most people, without the need for extra iodised salt in your diet. Too much salt isn’t good for your health, so it’s best to get iodine from other sources.

Why some people don’t get enough iodine

Some children in Australia – especially those in Victoria, Tasmania and New South Wales – don’t get quite enough iodine.

This might be because several areas of Australia have low iodine levels in the soil, meaning fruit, vegetables and livestock grown or raised in these areas don’t have much iodine.

Also, many families now cut salt out of their diets, leading to lower iodine intake.

Too much iodine

It’s possible to have too much iodine, but it’s quite hard to get a dangerously high level of it from food alone. For example, to have too much iodine, a child aged 1-3 years would need regularly to eat 1 kg of cheese or 25 whole boiled eggs or drink 4 glasses of milk in a day.

Some medicines and supplements might also contain high doses of iodine.

Some people are particularly sensitive to too much iodine, which might cause difficulties with their thyroid glands.

If you’re concerned about whether your child and family is getting enough iodine, it’s a good idea to talk with a health professional, like your GP or a dietitian.