Iodine is essential for thyroid hormone production and these hormones are essential for adequate brain and neurological development. This is particularly important during early pregnancy, lactation and early years of life. In fact, iodine is seen as a key nutrient for the first 1000 days of life (the time between a woman’s pregnancy to just before her child’s second birthday).
Iodine deficiency can range from mild to severe, with the most severe cases showing physically as a goitre, a large visible lump, in the neck. This is an adaptive reaction by the body where the thyroid in the neck will grow in size to trap the iodine. This kind of severe deficiency was eradicated in the UK in the 1960s and we are now more concerned about the hidden effects of iodine deficiency, especially on the brain.
Mild to moderate deficiency is an emerging area of research and we still know very little. However, studies have shown that low iodine intake during pregnancy can result in lower cognitive, language and motor scores at 18 months and 3 years; impaired working memory at 4 years, lower general cognitive and fine motor scores at 4-5 years; lower verbal IQ, language delay and lower reading and writing scores at 8 years old; lower reading accuracy and comprehension at 9 years old; and lower reading accuracy and comprehension at 9 years. However there are research gaps and more studies with cognitive outcomes in mild-moderate deficiency and randomised controlled trials are needed.
The recommendations for iodine in the UK for pregnancy and lactation are 140ug and this differs from other countries where these recommendations are increased during pregnancy and lactation. For example, in Australia and New Zealand, the recommendations are 220ug during pregnancy and 270ug during lactation. In the UK the recommendations are built on the basis that the mothers already have sufficient iodine stores that can be used and drawn upon to maintain and meet those requirements during pregnancy.
From the middle of pregnancy the foetus starts to produce its own thyroid hormones and it needs the building block of iodine to do this. This means that it is really important that the mother has a sufficient iodine intake, preferably pre-conception and then throughout her pregnancy. If she has sufficient stores of iodine in her thyroid then it can be used to meet her requirements. It is widely known that folic acid supplementation is vital pre-conception and for the first 12 weeks of pregnancy so perhaps the same message should apply to iodine intake.
Dietary sources of iodine: The main sources of iodine in the UK are milk and milk products. Other sources include fish, meat and meat products, eggs, bread, fruit, vegetables and potatoes. Although fish is a good source, the content varies between different species. For example, salmon and tuna contain around 10% of the recommended intake, whereas cod and haddock provide much more. Around 50% of the recommended intake can come from a glass of milk or a standard pot of yoghurt, however this will vary depending on the time of year. During summer, milk iodinecontent is lower than in winter because during winter the cattle are more reliant on mineral fortified feed than in the summer months when they have fresh grass. This makes it difficult to know exactly how much is in a glass of milk. Organic milk in the UK has quite a reasonable iodine concentration so it is a good source – around 50ug (⅓ adult requirements). For those on plant based diets or who are unable to have dairy, the iodine concentration of milk alternatives, compared to cows milk, have a very low iodine content (around 2% of cows milk). Fortified milks have a reasonable content so ensure that your milk alternative is fortified with iodine (Alpro has 225ug per 100ml, but notably not UHT, Koko dairy has 130ug, Asda Free from oat drink has 300ug). Vegetarians and vegans could be at risk of iodine deficiency and should ensure they are meeting their daily requirements. Supplements may be an option but avoid kelp supplements and do not exceed 150ug per day, especially in pregnancy.
As in most dietary recommendations, exceeding your requirements is not a good idea and could cause harm. Excessive iodine intake can lead to problems with thyroid function (hypo/hyperthyroidism). Seaweed can be high in iodine depending on the species and season and cooking affects iodine concentration. Kelp has a rich concentration and you will exceed requirements with just a 5g portion. This isn’t to say it shouldn’t be consumed but it should not be consumed as a regular source of iodine.
In summary: to meet your daily requirements, ensure a balanced diet containing good sources such as milk and milk products, fish, meat and vegetables. If you are following a plant based diet and your only sources are fortified milk alternatives, it may be beneficial to take a suitable supplement but avoid excessive intake by choosing one providing no more than 150ug daily. If you are planning a pregnancy, be mindful to think about iodine as well as other important nutrients such as folic acid, iron, calcium and vitamin D.