Milk in a jug and in a glass

What is iodine?

A dietitian explains what this trace element does in the body, its impact on thyroid hormones, how much we need for optimum health and the best food sources.

Iodine is a trace element that plays an important role in regulating thyroid hormones. You should be able to get all the iodine you need from a balanced and varied diet.


Always speak to your GP or healthcare provider before taking a new supplement or if you are concerned about nutritional deficiencies.

What is iodine?

Iodine is a trace element that is essential for the body to make thyroid hormones which play an integral role in the growth and development of cells and tissues. The body does not make iodine so it is essential to source it from a varied and balanced diet. Eating insufficient amounts of iodine can cause the thyroid to work harder to regulate levels. This means it may increase in size in order to hold on to and trap as much iodine as it can. This can lead to a swelling in the neck or a condition called ‘goitre’ – read more about this on the NHS website.

Why do we need iodine?

Iodine is critical for the correct function of the thyroid gland, especially before and during pregnancy and breastfeeding for the proper brain development of infants.

When iodine reaches the bloodstream, it is absorbed by the thyroid which then synthesises the thyroid hormones. These hormones are then secreted into the bloodstream and transported to different areas in the body.

How much iodine do we need and what are the effects of consuming too much?

Recommendations for iodine are 150mcg for adults and 200mcg for pregnant and lactating women. You should be able to get all the iodine you need from a balanced and varied diet, without the need for supplements.

Consuming too much iodine is not recommended. It is widely documented that iodine excess should be avoided as there may be harmful consequences for the production of thyroid hormones, both hypothyroidism (underactive thyroid gland) and hyperthyroidism (overactive thyroid gland).

Which foods are good sources of iodine?

Rich sources of iodine include dairy products, seafood and eggs. It is important to note there is a seasonal variation in the iodine content of milk – higher levels in winter milk rather than summer milk as cows are more reliant on mineral-fortified feed in the winter. Organic milk also has an iodine concentration that is over 40% lower than that of conventional milk. Brown seaweed such as kelp is a concentrated source of iodine and for this reason, should not be eaten more than once a week, especially during pregnancy.

Recipe suggestions

Seafood curry
One-pan summer eggs
Cheese, leek & potato tortilla
Seafood paella

More on vitamins and minerals

What is manganese?
What is zinc?
What is folic acid?
What is phosphorous?
What is potassium?

This article was published on 6 August 2019.

Emer Delaney BSc (Hons), RD has an honours degree in Human Nutrition and Dietetics from the University of Ulster. She has worked as a dietitian in some of London’s top teaching hospitals and is currently based in Chelsea.


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