Iodine

About iodine#

Iodine is used by the thyroid gland, in your neck, to make thyroid hormones. These hormones control your metabolic rate (the rate at which your body uses energy when it is resting) and help your brain and body grow and develop.

If there isn’t enough thyroid hormone circulating in your blood, your brain sends a chemical message to your thyroid gland to release more.

Iodine in food#

Iodine is found naturally in a range of foods, such as:

• dairy products
• seafood
• seaweed (kelp)
• eggs
• green leafy vegetables

The amount of iodine available in these foods depends on where the food was grown and how it was made. Some vegetables contain iodine, but only if they are grown in iodine-rich soils; in areas with low-iodine soils, most vegetables do not provide significant amounts.

Iodine can also come from iodized salt. However, adding salt to food can increase your risk of other health problems, such as high blood pressure and heart disease, so it is not recommended as a way to boost iodine. If you do choose to add salt, make sure it is labeled ‘iodized’. Note that, although it comes from the ocean, sea salt is not a good source of iodine.

In many countries, iodized salt is added to commercial bread products to increase the amount of iodine they contain. This is known as fortifying the bread with iodine, and it has helped improve the general population’s iodine status. Food regulators in some places also allow manufacturers to use iodized salt to fortify other products, as an alternative source for people who do not eat bread, provided it is labeled correctly.

Recommended dietary iodine intake#

You only need a very small amount of iodine compared to other nutrients (around one teaspoonful over a lifetime for most adults), which is why the recommended amounts are measured in micrograms (mcg, or µg). The recommended dietary intake (RDI) depends on your age and life stage.

Recommended dietary intakes (per day):

• Infants aged 0–6 months* — 90 µg
• Infants aged 7–12 months* — 110 µg
• Girls and boys aged 1–3 years — 90 µg
• Girls and boys aged 4–8 years — 90 µg
• Girls and boys aged 9–13 years — 120 µg
• Girls and boys aged 14–18 years — 150 µg
• Women and men aged 19 years and over — 150 µg
• Pregnant women — 220 µg
• Lactating women — 270 µg

*In very young children an RDI has not been set, so an Adequate Intake (AI) is used instead. This is an estimate based on the amount of iodine in the breastmilk of apparently healthy populations of young children.

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 that includes a wide variety of nutritious foods from the main food groups. For most people this provides enough iodine.

Some suggestions include:

• Have 2 to 3 serves of seafood each week. This provides iodine along with beneficial fish oils. Be mindful when choosing seafood, as some fish may have high levels of mercury or other chemicals (such as shark, orange roughy, swordfish and ling). If you are pregnant or planning to become pregnant in the next 6 months, avoid seafood that is high in mercury and choose lower-mercury varieties.
• Enjoy bread as part of a well-balanced diet, choosing wholegrain and high-fiber options where you can.
• Seaweed, dairy products and eggs also provide useful dietary iodine.

If you don’t get enough iodine in your diet, you may need to take a supplement. However, see your doctor before starting iodine supplements, as too much iodine can be harmful, especially if you have an underlying thyroid disorder.

Iodine deficiency#

If your diet is too low in iodine, your thyroid gland enlarges as it tries to trap more iodine from the bloodstream to make thyroid hormones. This overgrowth of the thyroid gland is called a goitre.

Goitre is not the only effect of not having enough iodine. People with long-term iodine deficiency can develop hypothyroidism, a condition in which not enough thyroid hormone is produced. Symptoms include dry skin, hair loss, fatigue and slowed reflexes.

Iodine in pregnancy#

Women who are pregnant or breastfeeding, as well as babies and very young children, are particularly at risk of problems from inadequate iodine intake. During pregnancy you need higher levels of iodine than usual for your baby’s healthy development.

• Mild to moderate iodine deficiency in pregnancy can affect a baby’s physical development and hearing, and cause learning difficulties.
• Severe iodine deficiency can cause major physical and neurological abnormalities, miscarriage or stillbirth.

Even where bread is fortified with iodine, pregnant women in many countries are still not getting enough to meet their needs. If you are pregnant, breastfeeding or considering becoming pregnant, ask your doctor for advice about your individual daily iodine needs. They may recommend that you take a daily supplement. If you have a pre-existing thyroid condition, do not take iodine supplements without checking with your doctor first.

Iodine deficiency in babies and children#

Iodine deficiency can cause serious problems for developing fetuses, babies and young children. If you are pregnant or breastfeeding and you are iodine deficient, your baby is particularly at risk. Deficiency can permanently affect your baby’s growth and mental and sexual development, and increase their risk of intellectual disability.

Lack of iodine is a major problem in developing countries and is the world’s leading cause of preventable intellectual disability in children.

Too much iodine can also be harmful#

Having too much iodine, for example through supplements, can cause some of the same problems as iodine deficiency (such as goitre). The level of iodine considered to be too much, and the symptoms experienced, can vary from person to person, depending on underlying health conditions.

If you think you are not getting enough iodine in your diet, speak to your doctor or an accredited dietitian before starting on any supplements.

Key points#

• Symptoms of iodine deficiency can include dry skin, hair loss, fatigue and slowed reflexes.
• Women, as well as babies and very young children, are particularly at risk of problems from inadequate iodine intake.
• Severe iodine deficiency can cause major physical and neurological abnormalities, miscarriage or stillbirth.
• Iodine deficiency can cause serious problems for developing fetuses, babies and young children.
• If you are pregnant or breastfeeding and you are iodine deficient, your baby is particularly at risk.

Where to get help#