Iodine deficiency. Do we need to worry?
Although thankfully now pretty rare in high income countries, micronutrient deficiencies do still very much exist, and remain a major cause of malnutrition globally. Iodine, one of the essential minerals, is increasingly in the spotlight as one to keep a beady eye on as dietary patterns and food production methods around the world continue to evolve.
For many years the UK wasn’t thought to have a problem with iodine deficiency, but recent studies have suggested otherwise, with the UK National Diet and Nutrition Survey (NDNS) finding that mild iodine deficiency may be a concern for 12% of young women. 1 in 8 reported intakes below the very lowest recommended daily amount (LRNI). A further study of 14-15 year old school girls in 2011, found that 51% were mildly deficient, although it should be said that the spot-test nature of most of the UK data means that there is some debate around the generalisability and accuracy of the results.
First off, what does iodine actually do?
Around 64% of the iodine in our bodies is stored in the thyroid gland. This gland is found in our necks - the HQ for production of the two thyroid hormones (T3 and T4) used to regulate the body’s metabolism. These hormones manage the speed of our metabolisms and so play a crucial part in controlling the rate at which we burn calories and regulate bodily temperatures.
Iodine is also important for looking after connective tissue between tendons and ligaments, and is critical for making sure that foetuses and young children develop and grow to their full potential, both physically and mentally.
Iodine is a great example of what I like to call the ‘Goldilocks paradigm’ when it comes to making sure we’re getting exactly the right amount of a micronutrient. Too much iodine and you may find yourself losing weight (hyperthyroidism), along with several other nasty side effects including heart palpitations, persistent fatigue, and sensitivity to heat. Too little iodine however, and you may struggle with an underactive thyroid (hypothyroidism), with side effects including weight gain, sensitivity to the cold, and depression.
In extreme cases of iodine deficiency the thyroid gland will swell, with these swellings called ‘goitres’, but this is rare in the UK and typically symptomatic of severe or long-term deficiency. Fun fact: the Derbyshire area of the UK used to be called ‘the Derbyshire goitre belt’, due to a high prevalence of goitre in this area for many centuries until around about the 1930s. Mountainous regions are often more likely to have iodine deficient populations given the lower amount of iodine in the soil which may explain it.
WHAT’S THE STORY?
Iodine deficiency disorders (IDD) is the umbrella term for the array of physical and mental development problems caused by iodine deficiency, affecting approximately 2 billion globally (29.8% of the population globally), and between 45% and 57% of the European population.
Although we don’t hear an awful lot about this mineral in the West, iodine deficiency is still a huge problem in many low and middle income countries (LMICs). In fact, the World Health Organisation describes iodine as the world’s most widely-occurring, yet happily also most preventable, cause of brain damage. As iodine plays an important part in the cognitive development of under-5’s cretinism can be the outcome of iodine deficiency in utero and in early development. As a result, since 1993 governments have attempted to end iodine deficiency by adding iodine to table salt.
On the whole, fortifying such a commonly used substance has been viewed as an unmitigated success. With salt iodisation a cheap and yet also very efficient process, UNICEF estimates that some 86% of households globally now have access to iodised salt. Well done world. Yet Perhaps ironically, this policy now leaves some European countries (where salt is not commonly iodised) more at risk of iodine deficiency.
It’s also worth noting that this policy has come in for some flak of late, given that salt also poses public health problems, with high levels of salt linked to hypertension (high blood pressure) which can increase the risk of cardiovascular issues. Never a dull moment in nutrition policy is there? With salt intakes rising in LMICs as traditional diets transition towards more processed, salt-heavy ‘Western’ foods, and with high-profile and long-running salt reduction campaigns ongoing in high income countries, salt iodisation is increasingly coming in for criticism. Given that average UK salt intakes are higher than the government currently recommends it’s unlikely that salt iodisation will be promoted as a potential mechanism for tackling iodine deficiency anytime soon.
Why are we worried now?
What’s interesting in the UK, is that for many years, dairy products have been a major contributor to iodine intake, accounting for approximately 33% of the intake in adults (19-64 years) and 40% in adolescents (11 to 18 years).
However, the decline in consumption of dairy products (particularly among the younger generation) has caused widespread consternation. With lactose intolerances and the numbers following vegan or exclusion diets increasing (particularly among good old millennials and generation X'ers) this trend looks set to continue, and is a major part of why we need to be talking about iodine again. The recent NDNS survey suggests that certain population groups are particularly vulnerable to iodine deficiency, so if you are a young girl (or responsible for one!), pregnant, or follow a vegetarian or vegan diet low in seafood and/or dairy products, consider taking a supplement or buying other products fortified with iodine.
HOW MUCH DO I NEED?
Adult men and women age 19 and over both need 140-150 μg per day. Pregnant women, or those conceiving, are recommended to take 200 ug per day.
WHAT ARE GOOD SOURCES?
Any foods from the sea, such as fish (particularly mackerel and haddock), shellfish, and seaweeds like kelp are naturally high sources of iodine. For those of you not looking forward to tucking into a nice seaweed salad - actually delicious - it can also be found in milk, vegetables, and grains. This is due to iodine working its way into the soil from the sea, where plant foods can absorb the mineral. However, as plant foods contain iodine only because of their environment, amounts can vary wildly depending on how iodine rich the soil is. For this reason, seaweed is not recommended a food to rely on for iodine, as there may be a danger of excess consumption
But, what on earth is a mineral found in the sea doing in your milk I hear you ask? Well, this is due to a quirk in food production. Cows don’t eat soil, but iodine is typically included in cattle feed and sterilizers which is why UK dairy products are a good source of iodine. Given that vegans and vegetarians are particularly vulnerable to iodine deficiency, it would be useful if more plant-based companies regularly fortified their products, but as this isn’t a mandatory policy few currently do. Of the plant ‘mylks’ commonly found on UK supermarket shelves, few fortify with iodine, with M&S branded alternative milk products a notable exception.
And one final note
This blog (and in fact, the entire website!), is in no way intended to panic anyone about potential deficiencies. See it more as a reminder about how important micronutrients are for a healthy life, quite easily as important as the more talked about macronutrients. You should consult a doctor right away if you suspect you’re deficient or are concerned about your thyroid.
General references
British Nutrition Foundation (2016) Nutrition Requirements. Available here.
Ursell, A. (2011) Vitamins & Minerals handbook. London, Dorling Kindersley Ltd. pp. 64-5.
World Health Organisation (2017). Micronutrient deficiencies, iodine deficiency disorders. Available here.
https://www.thyroidfoundation.org
https://www.bda.uk.com/foodfacts/Iodine.pdf
http://www.who.int/vmnis/database/iodine/iodine_data_status_summary_t2/en/