Iodine is an essential trace element in our diets and plays an important role in normal growth and development. Iodine deficiency is a significant public health problem worldwide1,2. It effects 2 billion people worldwide, and recently prevalence in the UK has increased, particularly among adolescent females and pregnant women3,4.
The Function of Iodine
Iodine is important for our thyroid functioning because it is involved in the synthesis of two thyroid hormones, T3 and T4, by the thyroid gland5. These are important in the controlling metabolism and for growth and development as well as in the development of the central nervous system and brain in foetus and children6,7.
Food Sources of Iodine
Dairy products, such as cow’s milk, yoghurt and cheese are our main dietary sources of iodine. Other good sources include; fish, shellfish, eggs and meat8. Smaller amounts of iodine can be found in some plant foods such as cereals and grains, however, levels vary depending on the geographical location of where they are grown9. Other plant-based foods such as fruits and vegetables can generally be poor sources of iodine10.
Whilst now some milk alternatives are fortified with iodine, research indicates they are still in the minority11,12, so it is important to read the food labels to check if they are fortified with iodine if consuming a more plant-based diet8.
Some countries add iodine to salt, “iodised salt”. Although it is possible to buy in some supermarkets, it is not commonly available in the UK8. Furthermore, the Government recommend to resultant intake, therefore it is not recommended to rely on iodised table salt as a way of increasing iodine intake8,13.
Iodine deficiency may result in inadequate production of thyroid hormones, having adverse effects on growth and development14. These effects can be grouped into an umbrella term, iodine-deficiency disorders14. Severe iodine-deficiency disorders can cause cretinism, characterised by severe learning disability and deafness14,15. Chronic low dietary intake of iodine will cause our thyroid to work harder to try and make the amount of thyroid hormones we need, causing our thyroid to increase in size to trap the iodine, this is called a “goitre”8,14,15.
Iodine-deficiency disorders in the UK were eradicated in the 1960’s due to the increase in milk-iodine concentration and increase in milk consumption, and so visible goitres are not commonly seen in the UK16. However, as indicated earlier, a UK national survey in 2011 found than there is an increase in mild iodine deficiency seen in adolescent girls and women of child-bearing age3,4.
Low dietary iodine may be due to low dairy or fish intake for example as consuming a plant-based diet, or due to living in an area with low iodine in soil for example living >100miles from the Ocean8,9.
Iodine Dietary Recommendations
For people over the age of 12 years old, the recommended iodine required is 150µg per day17.
For pregnant and breastfeeding women, the recommended iodine required is 150-250µg per day17. This increase during pregnancy and breastfeeding is to facilitate an increase in thyroid hormone production in the foetus or baby, to balance any potential losses from the mother and to supply to foetus with iodine so it can produce its own thyroid hormones after thyroid onset mid-gestation8,18.
There is currently no official recommendation in the UK for adults or pregnant women to take an iodine supplement, it is advised where possible to reach the iodine recommendations through our diets, and most adults following a balanced diet including dairy products and fish should be able to meet the recommendations9.
An iodine supplement may not be required during pregnancy if intake is adequate before and during pregnancy. Some pregnancy supplements do contain iodine, make sure that it does not provide more than 150mcg of iodine as the rest can be met through iodine8,9.
For further information about supplements, you can refer to the BDA fact sheet on iodine here.
It is possible to consume too much iodine and this can cause thyroid problems. Every person is different, but for the general population the guide is to not exceed 600mcg/day of iodine. People with thyroid disease or iodine-deficiency disorders may be affected differently, so check with a GP before taking supplements. Also be aware of kelp and seaweed which are food sources very rich in iodine and may lead to excessive iodine intake8,19.
• British Dietetic Association. Iodine: Food Fact Sheet8
• National Health Service. Vitamins and Minerals – Iodine9
• Iodine Global Network. The Iodine Blog20
Overall, if you are someone at increased risk of iodine deficiency, for example adolescent girls and women of child-bearing age or consuming a largely plant-based diet, check the labels of food products to see if and how much iodine is listed in the nutritional tables. You can contact a registered nutritionist, dietitian, or your GP for further advice.
This blog post was written by Emilia Fish, a registered associate nutritionist, Food Science and Nutrition BSc graduate and current Clinical and Public Health Nutrition MSc student at UCL. She has worked in several nutrition internship roles, has experience in Food Science labs and enjoys sharing simple, evidence-based nutrition on @nutritionnourishment. Emilia enjoys sharing others nutrition journeys in her podcast, The Nutrition Nourishment Podcast: Sharing Our Journeys.
Additional references to support this blog.
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