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What is iodine?

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A dietitian explains what this trace element does, 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. Most of us should be able to get all the iodine we need from a balanced and varied diet.

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Always speak to your GP or healthcare provider before taking a 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. These hormones play an integral role in the growth and development of cells and tissues and govern how fast our cells work. The body does not make iodine so it is essential to obtain 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. If this is the case it can lead to a swelling in the neck otherwise known as a ‘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 , when breastfeeding and for the proper brain development of infants.

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

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

Recommendations for iodine are 140mcg for adults and 200mcg for pregnant and lactating women. Most of us are able to get all the iodine we 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.

Seaweed is a source of iodine however, levels vary depending on the type of seaweed, its preparation and storage. Brown seaweed, like kelp, is a concentrated source and for this reason, should not be eaten more than once a week, especially during pregnancy.

If you are vegan or follow a plant-based diet you may need to pay more attention to where you obtain your iodine. This is because the amount of iodine in plant foods varies depending on how much is in the soil the plant was grown in. Some, but not all, plant ‘milks’ are fortified with iodine – check the label for potassium iodide on the ingredient list. Be aware, however, that fortified ‘milks’ may not necessarily supply the same amount of iodine as you’d achieve from the equivalent amount of dairy milk.

Seaweed in a bowl

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 reviewed on 5th July 2021 by Kerry Torrens.

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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All health content on bbcgoodfood.com is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other health care professional. If you have any concerns about your general health, you should contact your local health care provider. See our website terms and conditions for more information.

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