Iodine is one of the more curious essential minerals. You need it in tiny quantities, most of it lives in one small gland in your neck, and how much you get depends partly on the soil your food was grown in. Here's what iodine does, where to find it, how much you need, and when an iodine supplement can help.
What are the benefits of taking iodine?
Here's a fact worth knowing: your entire body contains only around 15 to 20 milligrams of iodine – less than a pinch of table salt if you held it in your hand. For comparison, your body holds roughly 3 to 4 grams of iron, which is hundreds of times more. But that tiny amount does an enormous amount of work.
And between 70% and 80% of it is concentrated in your thyroid gland, where it forms the building block for the hormones that keep your body running.
Iodine has five well-established roles:
· Thyroid function. Iodine contributes to the normal production of thyroid hormones and normal thyroid function. Your thyroid uses iodine to make T4 and T3, the hormones that regulate your metabolic rate, growth and energy levels.
· Energy. Iodine contributes to normal energy-yielding metabolism, helping your body turn food into fuel.
· Brain and nervous system. Iodine contributes to normal cognitive function and the normal functioning of the nervous system.
· Skin. Iodine contributes to the maintenance of normal skin.
Iodine also contributes to the normal growth of children, which is part of why it's given particular attention during pregnancy and infancy – thyroid hormones drive brain and nervous system development in the early years.
Which food is richest in iodine?
This one's trickier to answer than you might expect, because iodine content varies enormously depending on where food is grown. Most fruits and vegetables are poor sources, and the amounts they do contain depend on the iodine in the soil, along with fertiliser and irrigation practices. That variability carries through to meat and dairy, since it affects what the animals themselves are eating.
In the UK, most of our iodine comes from milk and dairy products. One cup of milk or three-quarters of a cup of Greek yoghurt provides over half your daily requirement, and eggs are a good source too. If you eat these regularly, you should be getting adequate amounts.
Fish and shellfish absorb iodine naturally from seawater, which makes cod, oysters and prawns rich sources – though they contribute less to overall intake simply because most people eat less than one portion a week.
Seaweed is the richest natural source by a considerable margin. A small amount can exceed your daily requirement several times over, which sounds ideal but is worth treating with care: the iodine content varies wildly between types, and it's genuinely possible to take in too much. Something to be particularly mindful of during pregnancy.
How much iodine do I need?
The NHS recommends 140µg of iodine a day for adults, and most people should be able to get all they need from a varied and balanced diet.
There are no UK-specific guidelines for pregnancy, though other health organisations recommend a higher intake. The World Health Organisation suggests 250µg a day, and European guidelines sit at 200µg.
If you do take a supplement, the Department of Health and Social Care advises that 0.5mg or less a day is unlikely to cause harm.
Who actually needs an iodine supplement?
As an essential trace mineral, iodine is needed in small amounts, and a balanced diet containing dairy, eggs or fish should comfortably cover your daily requirement.
The picture changes if you follow a plant-based or vegan diet. Plant foods contain very little iodine, and what they do contain depends on the soil they grew in, so if you don't eat fish, eggs or dairy, it's worth considering fortified foods or an iodine supplement. The same applies if you limit seafood or salt.
Iodine is one to get right rather than simply take more of. Taking high-dose supplements when you're not deficient can disrupt thyroid function, so it's genuinely worth speaking to your GP before starting one, particularly if you're pregnant or have a known thyroid condition.
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