What is iodine?

Why do we need iodine?

Iodine is critical for the correct function of our thyroid gland, as it’s needed to make the thyroid hormones – thyroxine and triiodothyronine – which regulate our metabolism. With inappropriate amounts of iodine, our thyroid hormones do not work properly, leading to conditions such as hypothyroidism (underactive thyroid gland) or hyperthyroidism (overactive thyroid gland). Our thyroid hormones play an integral role in the growth and development of cells and tissues, governing how fast our cells work. This is important whatever our age but even more so before and during pregnancy, when breastfeeding and for the proper brain development of infants.

Eating insufficient amounts of iodine can cause the thyroid to work harder. This means it may increase in size in an attempt to hold onto and trap as much iodine as it can. This can lead to a swelling in the neck known as a ‘goitre’ – read more about this on the NHS website.

Health benefits of iodine include:

• Supports thyroid function
• Regulates metabolism
• Important for infant growth and development

How much iodine do we need?

UK 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. However, if you do not eat fish or dairy you may need to consider your intake.

What are the effects of consuming too much iodine?

High iodine intakes are usually tolerated in most healthy people, but not recommended. Some people who have an autoimmune thyroid disease or have a history of chronic iodine deficiency can be sensitive to extra iodine and may experience symptoms. Excess iodine can come from supplements, eating certain sea vegetables and from salt containing iodine. Children, infants and the elderly are most at risk of iodine toxicity.

Symptoms of excess iodine include:

• Weight loss
• Fast or irregular heartbeat
• Hand tremors
• Irritability
• Fatigue
• Fever
• Burning sensation in the mouth, throat and stomach
• Nausea

What are the signs of an iodine deficiency?

The key role of iodine is to regulate your metabolism, so a deficiency can prevent normal growth and development, which is especially relevant for pregnant women and infants.

For adults, an iodine deficiency can lead to inadequate thyroid hormone production and a condition called hypothyroidism. This disrupts functions such as heart rate, body temperature and weight.

Signs of hypothyroidism include:

• Fatigue
• Weakness
• Sensitivity to cold
• Constipation
• Dry hair and skin

Which foods are good sources of iodine?

Dietary 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 are found in winter than summer milk as cows are more reliant on mineral-fortified feed in the winter. Furthermore, organic milk has an iodine concentration that is 40% lower than conventional milk.

Seaweed is a source of iodine, however levels vary depending on the type, preparation and storage. Brown seaweed, like kelp, is a concentrated source and many experts suggest it 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. Some, but not all, plant milks are fortified with iodine – check the label for ‘potassium iodide’ on the ingredients list. Be aware, however, that fortified milk may not necessarily provide the same amount as you’d achieve from the equivalent amount of dairy milk.

Useful food sources include:

• Seaweed, including kelp
• Fish (especially white fish) and shellfish
• Milk and dairy
• Eggs

Enjoy these recipes which contribute useful amounts of iodine

Seafood curry
One-pan summer eggs
Cheese, leek & potato tortilla
Seafood paella
Kelp and smoked salmon sushi rolls
Beetroot & avocado nori rolls with wasabi dipping sauce
Sushi burrito

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

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This article was reviewed on 17 November 2023 by Kerry Torrens.

Emer is a specialist dietitian who combines her love of food and science to help increase people’s awareness of a healthy lifestyle. An expert in IBS, weight loss and women’s health, she brings energy and passion to her profession and enjoys bringing the science of nutrition to life. In her ebook, IBS? Recipes For Success, Emer shares quick and easy recipes for people suffering from IBS, combining her passion for cooking with her expert knowledge. She has worked in top London teaching hospitals and balances her time between media work, private clients and NHS commitments.

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