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Nutrition

Iodine: function, foods, deficiency and supplements

23/11/20221 min read

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Iodine is important for thyroid hormones, the brain, skin and more. This piece is filled with information about iodine including food sources and deficiency.

Summary

1What is iodine and what does it do?

Iodine is an essential mineral needed to make thyroid hormones. These are important for: cell growth, brain development in early life, regulation...

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2What does iodine do in the body?

Iodine is critical for the healthy functioning of your body’s thyroid gland – in fact, 70-80% of your body’s iodine is stored in the thyroid...

Jump to details below

3Which foods are the best sources of iodine?

The best sources of iodine are: all seawater fish, especially white fish such as haddock and cod, shellfish, for example prawns and crab, dairy...

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What is iodine and what does it do?
What does iodine do in the body?
How much iodine do I need?
Do children need iodine?
Which foods are the best sources of iodine?
Who is at risk of an iodine deficiency?
What are the symptoms of an iodine deficiency?
What happens if I consume too much iodine?
When should I take iodine supplements?
Should women take an iodine supplement during pregnancy?
What are the potential benefits of taking an iodine supplement?
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Nutrition

Find out all about iodine, including what it does, how much you need, where to find it and who might need to supplement their diet

Written by Jack Feeney on January 2, 2019 Reviewed by Dr Sarah Schenker on January 23, 2019

What is iodine and what does it do?

Iodine is an essential mineral needed to make thyroid hormones. These hormones are important for:

cell growth
brain development in early life
regulation of metabolism

The European Commission reports that iodine can also contribute to normal cognitive function, maintain healthy skin, and support the functioning of the nervous system.¹

Iodine is mainly found in fish and dairy products. It’s also highly concentrated in certain marine algae, like kelp. However, if you eat seaweed frequently, you could risk getting too much iodine because it is toxic in large doses.²

Most people get enough iodine in their diets if they eat fish or dairy foods. However, schoolgirls, pregnant women, vegetarians and vegans are at risk of deficiency in the UK.³ Iodine is available in certain multivitamins and also in algae tablets, in which the iodine levels are restricted.

What does iodine do in the body?

Iodine is critical for the healthy functioning of your body’s thyroid gland – in fact, 70-80% of your body’s iodine is stored in the thyroid. The thyroid is responsible for the release of the two thyroid hormones, both of which require iodine to work:⁴

thyroxine (T4)
triiodothyronine (T3)

These hormones control the rate of cell metabolism – the speed at which your cells function – keeping us alive. Thyroid hormones have essential roles to play throughout the body, including:^5,6

brain development, including during pregnancy
heart function
muscle control
mood
digestive function

An iodine deficiency means the body can’t make enough thyroid hormones, and this can lead to hypothyroidism.⁷

How much iodine do I need?

Adults need 140mcg of iodine a day.⁸ However, if you are pregnant or breast-feeding, your body needs more: a total of 200mcg of iodine a day.⁹

Do children need iodine?

Iodine is important for your child’s growth and development. They need:¹⁰

1-3 years – 70mcg a day
4-6 years – 100mcg a day
7-10 years – 110mcg a day
11-14 years – 130mcg a day
15-18 years – 140mcg a day

Which foods are the best sources of iodine?

The best sources of iodine are:¹¹

all seawater fish, especially white fish such as haddock and cod
shellfish, for example prawns and crab
dairy foods, including cow’s milk, yoghurt and cheese
eggs
meat and poultry

The best plant sources of iodine are:¹²

seaweed
nuts
wholegrains
fruit and vegetables

For dairy and plant foods, the levels of iodine will vary depending on how much iodine is in the soil in that region.¹³

Who is at risk of an iodine deficiency?

People who don’t eat fish or dairy foods – and in particular vegans – could be at risk of an iodine deficiency.¹⁴Pregnant women and schoolgirls are reported to have such low intakes of iodine, that the World Health Organisation now classifies the UK as mildly iodine-deficient.¹⁵

What are the symptoms of an iodine deficiency?

A lack of iodine can trigger a condition called underactive thyroid, known as hypothyroidism. Symptoms include:16

tiredness
weight gain
feeling cold
depression
difficulty concentrating

Severe iodine deficiency can lead to an enlarged thyroid, known as a goitre, which appears as a visible swelling on the neck; the thyroid enlarges in order to trap more iodine. However, a severe iodine deficiency is very rare in the UK.¹⁷

In pregnancy, iodine deficiency can interfere with the normal brain development and growth of the unborn baby. In fact, a serious iodine deficiency is considered the most common cause of preventable brain damage in children worldwide.¹⁸

What happens if I consume too much iodine?

Too much iodine, as well as too little, can interfere with your thyroid function. For some, it causes goitre or hypothyroidism, with the same symptoms as above, but for others it can lead to hyperthyroidism, in which the body produces too many thyroid hormones.¹⁹

Symptoms of hyperthyroidism include:²⁰

anxiety
sweating
rapid heart rate
increased appetite but also weight loss
restlessness

When should I take iodine supplements?

You may need to take iodine supplements if you are:

vegan or vegetarian
pregnant or breast-feeding
don’t eat fish or dairy foods

Supplements containing up to 500mcg of iodine a day is considered safe for adults, according to the NHS.²¹

Should women take an iodine supplement during pregnancy?

It’s really important that you get enough iodine during pregnancy to support your baby’s developing brain – and ideally from a few months before you get pregnant. If you don’t eat fish or dairy foods, consider an iodine supplement or a pregnancy multivitamin that contains iodine.²²

Do not consume more than 500mcg a day, as the NHS warns this could cause thyroid problems for your baby.^23,24

What are the potential benefits of taking an iodine supplement?

Iodine is mainly given to help prevent and treat iodine deficiency disorders, and to encourage normal brain development in children. But a 2017 study in Frontiers in Immunology found that healthy iodine levels can also help regulate the body’s immune system.²⁵