What does iodine do?

Iodine is essential for the production of thyroid hormones which are vital for many body processes including metabolism and growth. One of the most important roles of the thyroid hormones, and therefore of iodine, is for development of the 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?

During pregnancy and breastfeeding

It is vital that women have good stores of iodine in the thyroid before becoming pregnant. Women of childbearing age should ensure that they meet the adult requirement, especially if planning a pregnancy. 

During pregnancy, the amount of iodine needed increases. This is because the mother has to make sufficient thyroid hormone for transfer to the baby to help its brain develop correctly. She also supplies all the iodine that the baby needs. Iodine deficiency in pregnancy may have serious consequences for the child so it is very important that pregnant women meet that higher iodine requirement.

During breastfeeding, the need for iodine remains high so that the mother can supply sufficient iodine in her breast milk to meet the requirements of the baby whose brain is still developing.

What happens if I do not have enough iodine?

Consuming low levels of iodine can have negative consequences for thyroid hormone production.
During pregnancy, a deficiency of iodine in the mother, even if mild, can lead to impaired brain development in the baby and this can have long-term implications for the child in later years, such as a lower IQ.

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. 

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 their main sources of iodine. Research has shown that organic milk has a 40% lower iodine-content than conventional milk. Organic milk and dairy products can still make an important contribution to iodine intake but if you consume them, you need to be aware that they will provide less iodine.

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.
 

*Actual iodine content will vary ‡Lower 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). If you have thyroid disease, 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.

Who is at risk of iodine deficiency?

Vegans are at risk of iodine deficiency as they do not eat rich iodine sources (fish and dairy products).  Vegetarians may also be at risk, especially if milk intake is low. 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.

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 needs for adults who do not consume sufficient iodine-rich foods. 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 a registered dietitian if you are uncertain.