What is iodine and why do I need it?

Iodine is an essential mineral which we need in small amounts to produce thyroid hormones.

The human body contains around 15–20 milligrams of iodine and most of this is stored in the thyroid gland in your neck.

Iodine is used by your thyroid gland to make two hormones: T4 (thyroxine) and T3 (triiodothyronine). These hormones regulate your metabolic rate.

Iodine is particularly important during pregnancy and early life, as the development of a baby's brain and nervous system is driven by thyroid hormones. Severe iodine deficiency during pregnancy can lead to brain damage, but even mild deficiency has been linked with impairments in cognition and school performance in childhood, external.

In the UK, the recommended daily intake of iodine is 140 micrograms, external, with no pregnancy-specific guidelines. But this is thought to be outdated, external.

Other health organisations encourage a higher intake during pregnancy. The World Health Organisation recommends 250 micrograms per day, and European guidelines sit at 200 micrograms per day.

Research has found that awareness of iodine's importance in pregnancy, external is low in women, and few mothers or mums-to-be feel confident about how to increase their intake.

In fact, girls aged 11 to 18 years and women of childbearing age (16 to 49 years) are less likely, external than other groups to have enough iodine.

This is tricky to answer as the amount of iodine in food varies depending on the soil or water it grows in.

Over time, ice, snow and rain have rinsed much of the iodine from the earth's surface soil, external into the sea, meaning there's less in our food.

So, in the UK iodine is added to animal feed and iodine-based sterilisers are used in milking. As a result, about 40% of our total iodine intake comes from milk and dairy foods.

Given that iodine ends up in the ocean, fish and shellfish are other good sources. Still, fish doesn't count hugely towards iodine intake in UK adults, because most people eat less than one portion a week.

Cod, baked

Crab

Mussels

Egg, boiled

Semi‑skimmed milk*

Yoghurt

Fortified soy milk

* There are slight differences in iodine content between skimmed, semi and full-fat milk, external and whether the milk's produced in winter or summer.

Over time, a lack of iodine can lead to hypothyroidism, external (or an 'underactive thyroid') where the thyroid gland can't make enough thyroid hormones. Symptoms of hypothyroidism include tiredness, dry skin, constipation and feeling sensitive to the cold.

Severe iodine deficiency is rare in the UK these days, and data from The National Diet and Nutrition Survey (NDNS) show that, overall, the iodine status of UK adults isn't bad.

But recent studies have found mild to moderate iodine deficiency in schoolgirls, external, women of child-bearing age and pregnant women in various parts of the UK. This is a concern because having a good iodine status is important for anyone planning to conceive.

Because there's no iodine fortification programme in the UK, iodine intakes depend on our personal food choices. Based on what the research shows and the lack of iodine in plant foods, people more at risk of deficiency include:

Milk, eggs and fish are all positively linked with iodine status, so if you eat these regularly, you should be able to get enough iodine. You could meet the recommended adult intake with a medium latte and small pot of yogurt, or eating a fish-based dinner like these cod and crab cakes.

If you are planning a pregnancy or are already pregnant, including a pregnancy multivitamin can help you meet the increased requirement consistently.

If you eat a plant-based diet, you'll need to supplement or choose a plant milk with added iodine, ideally 25 micrograms of iodine per litre.

At this level, 500ml a day (half a standard carton) contains almost 90% of the recommended daily intake. That could be achieved with a cup of plant milk in porridge and another cup in a latte, protein shake, smoothie or hot chocolate.

If you're at risk of iodine deficiency, a supplement can help. Most pregnancy multivitamins will contain between 140 and 200 micrograms, but check the label.

If you're considering a supplement, avoid seaweed ones as they can contain excessive levels which can be problematic. The NHS states that taking up to 500 micrograms is unlikely to cause any harm, though.

All content within this article is provided for general information only, and should not be treated as a substitute for the medical advice of your doctor or any other health care professional. Always consult your GP if you're concerned about your health.

Laura Tilt is a registered dietitian with a master's in public health nutrition and a postgraduate diploma in dietetics. Since qualifying in 2012, she has specialised in gastroenterology at London's UCLH before moving into freelance practice. With over 10 years of experience translating nutrition science into accessible, meaningful advice, Laura's specialist interests include digestive health, disordered eating, and sports nutrition.

Originally published August 2025. Updated February 2026.

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