Iodine is an essential nutrient for humans, but we need only a small amount of it for good health.
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 iodised soil, and in the products of animals that have grazed on soil with iodine in it.
Iodine is added to some foods, such as salt and commercially baked 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, dry skin, hair loss, tiredness, intolerance to cold and depression
- result in stunted growth, intellectual impairment and a lower level of intelligence measured by IQ.
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, breastfed babies depend on breastmilk as a source of iodine, which keeps their brains and nervous systems developing.
Severe iodine deficiency in a pregnant or breastfeeding woman might lead to brain damage in her fetus or baby.
If you’re trying to become pregnant or you’re pregnant or breastfeeding, always check with your doctor about your individual needs. If you’re worried about your iodine intake, your doctor can use a simple urine test to check your levels.
Sources of iodine
Including the following foods in your family’s diet each week will help to ensure that you and your children are getting enough iodine:
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: experts recommend 2-3 meals of regular seafood (for example, fish such as tinned salmon or tuna) per week. If you’re pregnant, you should be careful when choosing fish. That’s because some fish – such as flake, swordfish and barramundi – have higher levels of mercury than others.
Eggs, meat, vegetables and dairy products: vegetarians might also need to consider iodine supplements or iodine-rich foods such as soy milks that include extracts of seaweed.
The amount of iodine in different foods such as bread and milk varies between brands so the amount of food required to meet dietary needs also varies.
Iodised salt is a rich source of iodine and has replaced non-iodised salt in all bread 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.
How much iodine people need
The Nutrient Reference Values for Australia and New Zealand recommend the following daily intake of iodine:
- Young babies aged 0-6 months need 90 micrograms (μg) per day.
- Older babies aged 7-12 months need 110 μg per day.
- Children aged 1-8 years need 90 μg per day.
- Children aged 9-13 years need 120 μg per day.
- Teenagers aged 14-18 years and adults who are neither pregnant nor breastfeeding need 150 μg per day.
- Pregnant women, women trying to become pregnant and breastfeeding women should take an iodine supplement of 150 micrograms (μg) each day.
Why some people don’t get enough iodine
Some Australian children – 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 vegetables grown in these areas don’t have much iodine.
Many families now cut salt out of their diets, leading to lower iodine intake. Even when they add salt to their meals, it’s often in the form of regular salt or sea salt, rather than iodised table salt.
Too much iodine
It’s possible to have too much iodine, but consuming a dangerously high level of it is actually quite hard. For example, your child would need to eat 1 kg of cheese or 25 whole boiled eggs or drink 5 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 thyroid glands. Some medications and supplements might also contain high doses of iodine.
If you’re concerned about your family’s daily iodine intake, start by speaking with your GP or a dietitian