Iodine Facts

This advice is for adults only (including pregnant and breastfeeding women); it is not suitable for children.

This sheet is for information only. It is not intended to replace medical diagnosis or other dietary information you have been given. Follow advice on foods to avoid if you are pregnant. Consult a dietitian or your GP if you are unsure about any information. If you need to see a dietitian, visit your GP for a referral or: for a private dietitian. Check that your dietitian is registered at Written by Dr Sarah Bath, Dietitian and Professor Margaret Rayman © University of Surrey. June 2012

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What does iodine do?

Photo of thyroid

Iodine is a mineral that is important for health. It is needed to make hormones in the thyroid. These hormones are needed for many body processes including growth, metabolism and for the development of a baby’s brain during pregnancy and early life.


Do we get enough iodine in the UK?

For many years iodine intake in the UK was thought to be more than adequate but recent research has shown mild iodine deficiency in schoolgirls and pregnant women. There is now concern that many people may not be getting enough iodine.


How much iodine do I need?

Life stage

Iodine required per day (mcg)*



Pregnant women


Breastfeeding women


*WHO requirements


Before and during pregnancy and breastfeeding 

As iodine is required from the early stages of pregnancy, you should make sure you have been having enough iodine in your diet for several months before you get pregnant. This is because you can build up good stores of iodine in your thyroid before you become pregnant which helps it to function well during pregnancy. Therefore if you are of childbearing age, and especially if you are planning a pregnancy, you should ensure that you meet the adult requirement for iodine.

During pregnancy, the amount of iodine you need increases. This is because you have to make sufficient thyroid hormones to transfer to your baby to help its brain develop correctly. You also supply all the iodine that the baby needs. Iodine deficiency in pregnancy may have serious consequences for your child so it is very important that you meet that higher iodine requirement if you are pregnant. Breastfeeding mums still need a higher amount of iodine, so their breast milk has enough iodine for their baby. This is because the brain is still developing.


What happens if I do not have enough iodine?

A low intake of iodine over a long period of time may cause the thyroid gland in the neck to increase in order to trap iodine; this swelling may be visible and is known as goitre. However, visible goitre due to low iodine intake is rare in the UK. 

It is more likely that having too little iodine in your diet will lead to low levels of thyroid hormones. If you

iodine blackboard

have a deficiency of iodine when you are pregnant, your baby’s brain may not develop as well as it could and this could affect your child’s ability to learn in later years; for instance, your child could have a lower IQ or poorer reading ability.


Where is iodine found in the diet?

Iodine is found in range of foods, the richest sources being fish and dairy products. Although seaweed is a concentrated source of iodine, it can provide excessive amounts (particularly brown seaweed e.g. kelp) and therefore eating it more than once a week is not recommended, especially during pregnancy.

For most people, milk and dairy products are theirPhoto of cheeseboard main sources of iodine. Research has shown that organic milk has a 40% lower iodine-content than conventional milk. 

In many countries, iodine is added to table salt to give “Iodised salt”. Iodised salt is not widely available in the UK but can be found in some branches of several supermarket chains. As government recommendations are to reduce salt intake for health reasons, you should not rely on iodised salt as a means of increasing your iodine intake.


The actual amount of iodine in food varies according to the soil iodine-content, farming practice, fish species and season. For example, winter milk has higher levels of iodine than summer milk. This makes estimating iodine per portion difficult. The figures in the table are therefore for guidance only. Remember to follow Government advice on foods to avoid during pregnancy.



Portion (g)

Average iodine/portion (mcg)*

Conventional milk (cows’)



Organic milk (cows’)



Conventional yoghurt (cows’)‡



Eggs (hens’)

1 egg: 50g


Cheese (cows’)‡



White fish



Oily fish
















1 slice: 36g


Fruit & vegetables

1 portion: 80g


*Actual iodine content will varyLower iodine concentration for organic **Depending on the season, higher value in winter


Can I have too much iodine?

Yes; excessive iodine intake can cause thyroid problems. As a guide, intakes should not regularly exceed 600 mcg/day (less in children).


Who is at risk of iodine deficiency?

Anyone who avoids fish and/or dairy products (e.g. due to allergy or intolerance) could be at risk of iodine deficiency. Soya milk is often not fortified with iodine (check the label) and therefore will not replace the iodine in cows’ milk. Vegetarians and particularly vegans are at risk of iodine deficiency as they do not eat rich iodine sources (fish and/or dairy products).


What about an iodine supplement?

Most adults following a healthy, balanced diet containing milk, dairy products and fish, should be able to meet their iodine requirements.

A supplement containing iodine can help meet iodine Photo of cheeseboardneeds for adults who do not consume sufficient iodine-rich foods. If you have thyroid disease, are taking other medications or have experienced iodine deficiency over many years, you should speak with your GP before taking additional iodine. This is because you may respond differently to extra iodine. Iodine in supplements should be in the form of ‘potassium iodide’ and should not exceed the daily adult requirement of 150 mcg.

Seaweed or kelp supplements should not be used as an iodine source. This is because the amount of iodine in the supplement can vary considerably from the value claimed on the label and can provide excessive quantities of iodine.

It can be difficult to meet the higher recommendations for iodine during pregnancy and breastfeeding through diet alone, especially if you do not eat rich sources of iodine. Many, but not all, multivitamin and mineral pregnancy supplements contain iodine, so you need to check the label. The supplement should provide up to 150 mcg, so the remainder of the requirement can be met by your diet. If you consume high quantities of iodine-rich foods during pregnancy, you may not need an iodine supplement; talk to your doctor if you are uncertain.



Iodine is important for the production of thyroid hormones. It is dangerous to have too little or too much Iodine. Good dietary sources include fish, shellfish and dairy products. During pregnancy, iodine is essential for the correct development of the baby’s brain.






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